The more formal optimization process is typically referred to as  forward planning  and  inverse planning . [ 12 ] [ 13 ]
Plans are often assessed with the aid of  dose-volume histograms , allowing the clinician to evaluate the uniformity of the dose to the diseased tissue (tumor) and sparing of healthy structures.


In forward planning, the planner places beams into a radiotherapy treatment planning system that can deliver sufficient radiation to a  tumour  while both sparing critical  organs  and minimising the dose to healthy tissue. The required decisions include how many radiation beams to use, which angles each will be delivered from, whether attenuating  wedges  be used, and which MLC configuration will be used to shape the radiation from each beam.


Once the treatment planner has made an initial plan, the treatment planning system calculates the required monitor units to deliver a prescribed dose to a specific area, and the distribution of dose in the body this will create. The dose distribution in the patient is dependent on the anatomy and beam modifiers such as wedges, specialized collimation, field sizes, tumor depth, etc. The information from a prior  CT scan  of the patient allows more accurate modelling of the behaviour of the radiation as it travels through the patient's tissues. Different dose calculation models are available, including  pencil beam ,  convolution-superposition  and  monte carlo simulation , with precision versus computation time being the relevant trade-off.


This type of planning is only sufficiently adept to handle relatively simple cases in which the tumour has a simple shape and is not near any critical organs.


In inverse planning a radiation oncologist defines a patient's critical organs and tumour, after which a planner gives target doses and importance factors for each. Then, an optimisation program is run to find the treatment plan which best matches all the input criteria. [ 14 ]


In contrast to the manual trial-and-error process of forward planning, inverse planning uses the optimiser to solve the  Inverse Problem  as set up by the planner. [ 15 ]


Radiation-induced lumbar plexopathy (RILP)  or  radiation-induced lumbosacral plexopathy (RILSP)  is nerve damage in the pelvis and lower spine area caused by therapeutic radiation treatments.  RILP is a rare side effect of  external beam radiation therapy [ 1 ] [ 2 ] [ 3 ]  and both  interstitial and intracavity brachytherapy  radiation implants. [ 4 ] [ 5 ]   RILP is a  Pelvic Radiation Disease  symptom. [ 6 ]


In general terms, such nerve damage may present in stages, earlier as  demyelination  and later as complications of  chronic radiation fibrosis . RILP occurs as a result of  radiation therapy  administered to treat  lymphoma  or cancers within the abdomen or pelvic area such as cervical, ovarian, bladder, kidney, pancreatic, prostate, testicular, colorectal, colon, rectal or anal  cancer . [ 7 ] [ 8 ]  The  lumbosacral plexus  area is  radiosensitive  and  radiation plexopathy  can occur after exposure to mean or maximum radiation levels of 50-60  Gray [ 7 ]  with a significant rate difference noted within that range. [ 9 ]


Lumbosacral plexopathy is characterized by any of the following symptoms; usually bi-lateral and symmetrical, though unilateral is known. [ 8 ]


Symptoms are typically a step-wise progression with periods of stability in between, [ 1 ] [ 3 ]  weakness often appearing years later. [ 8 ]   Weakness frequently presents in the lower leg muscle groups. [ 8 ]   Symptoms are usually irreversible. [ 10 ]


Initial onset of symptoms may occur as early as 2 [ 8 ]  to 3 [ 11 ] [ 1 ]  months after radiotherapy.  The median onset is approximately 5 years, [ 8 ]  but can be highly variable, 2-3 decades after radiation therapy. [ 8 ]  One case study recorded the initial onset occurring 36 years post treatment. [ 12 ]


The treatment's ionizing radiation is an activation mechanism for  apoptosis (cell death)  within the targeted cancer, [ 13 ]  but it can also impact nearby healthy radiosensitive tissues, like the  lumbosacral plexus . The occurrence and severity of RILP is related to the magnitude of  ionizing radiation [ 10 ]  and the  radiosensitivity  of peripheral nerves may be further aggravated when combined with chemotherapy, like taxanes and platinum drugs, during treatment. [ 14 ]


The  pathophysiological process  behind radiation's RILP nerve damage has been discussed since the 1960s [ 10 ]  and is still without a precise definition. [ 1 ] [ 13 ]   Consensus does exist on a progression of RILP symptoms, with a stepping (a time delay) between two periods of plexopathy onset, the first from radiation injury and the later from fibrosis. Proposed mechanisms of the early nerve damage include microvascular damage ( ischemia ) supplying the myelin, [ 1 ]  radiation damage of the myelin, [ 15 ]  and oxygen free radical cell damage. [ 1 ] [ 15 ]  The delayed nerve damage is attributed to  compression neuropathy [ 1 ]  and a late fibro-atrophic ischemia from retractile fibrosis. [ 1 ] [ 15 ]


The more common source of lumbar  plexopathy  is a direct or secondary [ 2 ]  tumor involvement of the plexus with  MRI  being the typical confirmation tool. [ 15 ]  Tumors typically present with enhancement of nerve roots and T2-weighted hyperintensity. [ 2 ]  The differential consideration of RILP requires taking a  medical history  and neurologic examination. [ 15 ]


RILP's neurological symptoms can mimic other nerve disorders. People may present with pure lower motor neuron syndrome, a symptom of  amyotrophic lateral sclerosis (ALS) . [ 4 ] [ 16 ]  RILP may also be misdiagnosed as   leptomeningeal metastasis  often showing nodular  MRI  enhancement of the  cauda equina nerve roots  or having increased  CSF protein content . [ 4 ]


Other differential diagnoses to consider are  Chronic Inflammatory Demyelinating Polyradiculoneuropathy ,  neoplastic lumbosacral   plexopathy,  paraneoplastic neuronopathy ,  diabetic lumbosacral plexopathy ,  degenerative disk disease  ( osteoporosis of the spine ),  Osteoarthritis of the spine ,  Lumbar Spinal Stenosis , post-infectious plexopathy,  carcinomatous meningitis (CM) ,  mononeuritis multiplex , and  chemotherapy-induced plexopathy . [ 1 ]


The testing to resolve a RILP diagnosis involves  blood serum  analysis,  X-rays ,  EMG , MRI and  cerebrospinal fluid   analysis . [ 2 ] [ 1 ] [ 15 ]


Since RILP's neurological changes are typically irreversible and a curative strategy has yet to be defined, prevention is the best approach. [ 1 ]  Treating the primary cancer remains an obvious requirement, but lower levels of lumbar plexus radiation dosing will minimize or eliminate RILP. [ 1 ] [ 15 ]


One method to reduce the lumbosacral plexus' dosing is to include it with other at-risk organs that get spared from radiation. [ 17 ] [ 18 ]


Key to prevention is resolving the lack of clinical evidence between radiation treatments and the onset of neurological problems. That relationship is hidden by RILP's low toxicity rate, the lack of a large monitored population size and the lack of data pooling across multiple institutions. [ 1 ] [ 19 ]


Treatment of RILP is primarily supportive [ 15 ]  with mental, [ 2 ] [ 10 ]  physiological [ 2 ] [ 1 ] [ 10 ] [ 15 ]  and social aspects [ 10 ]  and consideration of any aggravating (synergistic) neurological factors. [ 1 ] [ 10 ]


To prevent compounding existing RILP symptoms and to minimize further progression


The effect on the person with the condition, depends upon the type of impairment. Handicaps may include physical challenges, bowel and/or bladder dysfunction and may occur in multiple settings of work and home. [ 10 ]   Physical  and  occupational therapy  are important elements in maintaining mobility and use of the lower extremities, along with assistive aides such as  Ankle-Foot-Orthotics (AFOs) , cane, walkers, etc. [ 2 ] [ 10 ] [ 15 ]  Sensory reeducation techniques may be necessary for balance [ 2 ]  and  lymphedema  management may be required. [ 10 ]


Pharmaceuticals that may be effective for RILP's  neuropathic pain  are


Non-pharmaceutical RILP considerations are


Functional impairment and residual pain can lead to social isolation. [ 10 ]  Cancer support groups are valuable resources to learn about the syndrome and therapeutic options, and are a means to voice emotions related to having cancer and surviving it. [ 10 ] [ 1 ] [ 15 ]


With increasing cancer treatment survival rates, the quality of life for its survivors has become a public health priority. [ 1 ]   The effects of RILP can be debilitating.  With no effective treatment to control radiation damage's progressive nature, limb dysfunction is the likely result. [ 10 ]


Radiation damage's outcome is related to its initial onset time.


An exact occurrence rate has  not  been established.  Literature  on  the topic  is  sparse. [ 21 ]  Clinical occurrences of RILP are rare, affecting between 0.3 and 1.3% of those treated with abdominal or pelvic radiation. [ 2 ]  The incidence rate is  variable, dependent upon the irradiated zone, dosage level and method of delivery. For example, when alternate dosing levels were compared, higher rates were observed, from 12 to 23%, the higher RILP rates occurring with higher dosages. [ 21 ]


As of 1977 lumbosacral neuropathy arising from  radiation therapy  had been rarely reported.  One of the earliest cases was in 1948. [ 7 ] [ 11 ] [ 22 ]


The incidence rate of peripheral neuropathy has been demonstrated to decrease when lower therapeutic radiation dosing levels are used. [ 21 ] [ 1 ]   A similar nerve injury,  Radiation-induced Brachial Plexopathy (RIBP) , may occur secondary to breast radiation therapy. [ 23 ]   Studies on RIBP have observed the  brachial plexus'  radiosensitivity.  Injury was observed after dosages of 40 Gy in 20 fractions and RIBP significantly increased with doses greater than 2 Gy per fraction. [ 21 ]   RIBP is more common than lumbosacral radiculoplexopathy [ 4 ]  and has a clinical history with reduced dosing levels.  RIBP occurrence rates were in the 60% range in the 1960s when 60 Gray treatments were applied in 5 Gray  fractions ; RIBP occurrences in the 2010s approach 1% with 50 Gray treatments applied in 3 Gy fractions. [ 1 ]


RILP occurrence rates are estimated at 0.3% to 1.3%, though the actual rate is likely higher. The soft tissue damage leading to RILP is more commonly seen with exposure levels over 50 Gy, though has occurred with as little as 30 Gy. [ 24 ]   A major step toward reducing RILP occurrences is by limiting the lumbosacral plexus' dosing level when treating pelvic malignancies, limiting the mean dose to < 45 Gy.  One approach to reduced levels, the plexus' mapping  with other  organs at risk , was clinically evaluated during the 2010s. [ 17 ] [ 18 ]


Clinical evidence of the cause-and-effect for prevention and the management of radiation induced polyneuropathy is limited. [ 10 ]


In 2011 the Radiation Oncology Institute (ROI) announced the National Radiation Oncology Registry (NROR). ROI and  Massachusetts General Hospital  would initially focus the NROR on prostate cancer, collecting efficacy and side effect information (like radiation induced neuropathy, RILP) from people treated with radiotherapy. [ 25 ]  In 2013 the  American Society for Radiation Oncology (ASTRO)  joined the effort [ 26 ]  and the number of data collection sites increased to 30 for a 1-year pilot project.  Pitfalls of medical data collection arose with only 14 sites being able to provide data and all those requiring significant manual entry efforts. [ 27 ]   The first NROR project conclusion was that future registries would need to cope with  Big data analytics . In 2015 ASTRO, the  National Cancer Institute  and the  American Association of Physicists in Medicine  sponsored a Big Data Workshop at the National Institutes of Health.


Experimental approaches for RILP treatment and management include:


This article incorporates text in the  public domain  from the 20th edition of   Gray's Anatomy   (1918)


Radiation-induced lung injury  ( RILI ) is a general term for damage to the  lungs  as a result of exposure to  ionizing radiation . [ 1 ]  In general terms, such damage is divided into early  inflammatory  damage ( radiation pneumonitis ) and later complications of chronic  scarring  ( radiation fibrosis ). Pulmonary radiation injury is an  unavoidable risk  of  radiation therapy  administered to treat thoracic or  lung cancer . [ 2 ]


The  lungs  are a  radiosensitive  organ, and radiation  pneumonitis  can occur leading to  pulmonary insufficiency  and death (100% after exposure to 50 gray of radiation) in a few months. Radiation  pneumonitis  is characterized by:


Symptoms of radiation pneumonitis include:  fever ,  cough , chest congestion,  shortness of breath , chest pain


High resolution CT thorax


“The Canadian Cancer society mentions these things that help to manage radiation,


Your healthcare team may recommend medicines to treat radiation pneumonitis, such as:


decongestants
cough suppressants
bronchodilators
corticosteroids to reduce inflammation
oxygen therapy
You can also try the following to help manage symptoms:


Rest if you feel short of breath.
Drink more fluids and use a cool-air vaporizer or humidifier to keep the air moist.
Use an extra pillow to raise your head and upper body while resting or sleeping.
Avoid the outdoors on hot, humid days or very cold days (which can irritate the lungs).
Wear light, loose-fitting tops and avoid anything tight around the neck, such as ties or shirt collars.“ [ 3 ]


For more information go to their website, as they have accurate information. “More Info”


Radioimmunotherapy  (RIT) uses an  antibody  labeled with a  radionuclide  to deliver  cytotoxic  radiation to a target cell. [ 1 ]  It is a form of  unsealed source radiotherapy . In  cancer therapy , an antibody with  specificity  for a tumor-associated  antigen  is used to deliver a lethal dose of  radiation  to the tumor cells.  The ability for the antibody to specifically bind to a tumor-associated antigen increases the dose delivered to the tumor cells while decreasing the dose to normal tissues.  By its nature, RIT requires a tumor cell to express an antigen that is unique to the  neoplasm  or is not accessible in normal cells.


131 I tositumomab and  90 Y ibritumomab tiuxetan were the first agents of radioimmunotherapy, and they were approved for the treatment of refractory  non-Hodgkin's lymphoma .  This means they are used in patients whose lymphoma is refractory to conventional  chemotherapy  and the monoclonal antibody  rituximab .


A set of radioimmunotherapy drugs that rely upon an  alpha-emitting  isotope (e.g.,  bismuth-213  or, preferably,  actinium-225 ), rather than a  beta emitter , as the killing source of radiation is being developed. Several  phase II clinical trials  for the treatment of  acute myeloid leukemia  have been carried out using alpha-emitting RITs. [ 10 ] [ 11 ]


90 Y-FF-21101 is a monoclonal antibody against  P-cadherin   radiolabeled  with  yttrium-90 . [ 12 ]  It is one of several RIT treatments under investigation intending to treat  solid tumors . [ 13 ]  A  phase I clinical trial  began in 2015. [ 14 ]


Other types of cancer for which RIT has therapeutic potential include  prostate cancer , [ 15 ]  metastatic  melanoma , [ 16 ]   ovarian cancer , [ 17 ]   neoplastic meningitis , [ 17 ]   leukemia , [ 18 ]  high-grade brain  glioma , [ 19 ]  and metastatic  colorectal cancer . [ 20 ]


Components of the extracellular matrix and the tumor microenvironment can also be targeted by radioimmunotherapy, such as Netrin-1  [ 21 ]  (an axon guidance protein) and FAP (a marker for cancer associated fibroblasts). [ 22 ]


Radiopharmacology  is  radiochemistry  applied to  medicine  and thus the  pharmacology  of radiopharmaceuticals ( medicinal radiocompounds , that is,  pharmaceutical drugs  that are  radioactive ). Radiopharmaceuticals are used in the field of  nuclear medicine  as  radioactive tracers  in  medical imaging  and in  therapy  for many  diseases  (for example,  brachytherapy ). Many radiopharmaceuticals use  technetium-99m  (Tc-99m) which has many useful properties as a  gamma-emitting   tracer   nuclide . In the book  Technetium  a total of 31 different radiopharmaceuticals based on Tc-99m are listed for imaging and functional studies of the  brain ,  myocardium ,  thyroid ,  lungs ,  liver ,  gallbladder ,  kidneys ,  skeleton ,  blood  and  tumors . [ 1 ]


The term  radioisotope , which in its general  sense  refers to any radioactive  isotope  ( radionuclide ), has historically been used to refer to all radiopharmaceuticals, and this usage remains common. Technically, however, many radiopharmaceuticals incorporate a  radioactive tracer  atom into a larger pharmaceutically-active molecule, which is localized in the body, after which the radionuclide tracer atom allows it to be easily detected with a  gamma camera  or similar gamma imaging device. An example is  fludeoxyglucose  in which  fluorine-18  is incorporated into  deoxyglucose . Some radioisotopes (for example  gallium-67 ,  gallium-68 , and  radioiodine ) are used directly as soluble ionic salts, without further modification. This use relies on the chemical and biological properties of the radioisotope itself, to localize it within the body.


See  nuclear medicine .


Production of a radiopharmaceutical involves two processes:


Radionuclides used in radiopharmaceuticals are mostly radioactive  isotopes  of elements with atomic numbers less than that of  bismuth , that is, they are radioactive isotopes of elements that also have one or more stable isotopes. These may be roughly divided into two classes:


Because radiopharmeuticals require special licenses and handling techniques, they are often kept in local centers for medical radioisotope storage, often known as  radiopharmacies . A  radiopharmacist  may dispense them from there, to local centers where they are handled at the  practical medicine  facility.


As with other pharmaceutical drugs, there is  standardization  of the  drug nomenclature  for radiopharmaceuticals, although various standards coexist. The  International Nonproprietary Name  (INN) gives the base drug name, followed by the radioisotope (as mass number, no space, element symbol) in parentheses with no superscript, followed by the ligand (if any). It is common to see square brackets and superscript superimposed onto the INN name, because  chemical nomenclature  (such as IUPAC nomenclature) uses those. The  United States Pharmacopeia  (USP) name gives the base drug name, followed by the radioisotope (as element symbol, space, mass number) with no parentheses, no hyphen, and no superscript, followed by the ligand (if any). The USP style is not the INN style, despite their being described as one and the same in some publications (e.g.,  AMA , [ 4 ]  whose style for radiopharmaceuticals matches the USP style). The  United States Pharmacopeial Convention  is a sponsor organization of the  USAN Council , and the  USAN  for a given drug is often the same as the USP name.


Radium-223   ( 223 Ra, Ra-223) is an  isotope  of  radium  with an 11.4-day  half-life . It was discovered in 1905 by T. Godlewski, [ 2 ] [ 3 ] [ 4 ]  a Polish chemist from  Kraków , and was historically known as  actinium X  (AcX). [ 5 ] [ 6 ]  Radium-223 dichloride is an alpha particle-emitting radiotherapy drug that mimics calcium and forms complexes with hydroxyapatite at areas of increased bone turnover. [ 7 ]  The principal use of radium-223, as a  radiopharmaceutical  to treat  metastatic  cancers in  bone , takes advantage of its chemical similarity to  calcium , and the short range of the  alpha radiation  it emits. [ 8 ]


Although radium-223 is naturally formed in trace amounts by the  decay of uranium-235 , it is generally made artificially, [ 9 ]  by exposing natural radium-226 to  neutrons  to produce radium-227, which decays with a 42-minute half-life to  actinium-227 .  Actinium-227 (half-life 21.8 years) in turn decays via  thorium-227  (half-life 18.7 days) to radium-223. This decay path makes it convenient to prepare radium-223 by "milking" it from an actinium-227 containing generator or "cow", similar to the  moly cows  widely used to prepare the medically important isotope  technetium-99m . [ 9 ]


223 Ra itself  decays  to  219 Rn  (half-life 3.96 s), a short-lived gaseous  radon  isotope, by emitting an  alpha particle  of 5.979  MeV . [ 1 ]


The pharmaceutical product and medical use of radium-223 against skeletal metastases was invented by Roy H. Larsen, Gjermund Henriksen and Øyvind S. Bruland [ 13 ]  and has been developed by the former Norwegian company  Algeta  ASA, in a partnership with  Bayer , under the trade name  Xofigo  (formerly  Alpharadin ), and is distributed as a solution containing radium-223 chloride (1100 kBq/ml), sodium chloride, and other ingredients for intravenous injection. Algeta ASA was later acquired by Bayer who is the sole owner of Xofigo. [ 12 ] [ 14 ]


The use of radium-223 to treat metastatic bone cancer relies on the ability of  alpha radiation  from radium-223 and its short-lived decay products to kill cancer cells.  Radium is preferentially absorbed by bone by virtue of its chemical similarity to calcium, with most radium-223 that is not taken up by the bone being cleared, primarily via the gut, and excreted. [ 15 ]  Although radium-223 and its decay products also emit  beta  and  gamma radiation , over 95% of the decay energy is in the form of alpha radiation. [ 16 ]  Alpha radiation has a very short range in tissues compared to beta or gamma radiation: around 2–10 cells. This reduces damage to surrounding healthy tissues, producing an even more localized effect than the beta-emitter  strontium-89 , also used to treat bone cancer. [ 17 ]  Taking account of its preferential uptake by bone and the alpha particles' short range, radium-223 is estimated to give targeted  osteogenic cells  a radiation dose at least eight times higher than other non-targeted tissues. [ 11 ]


The phase II study of radium-223 in  castration-resistant prostate cancer  (CRPC) patients with  bone metastases  showed minimum  myelotoxicity  and good tolerance for the treatment. [ 18 ]


223 Ra successfully met the primary endpoint of  overall survival  in the  phase III  ALSYMPCA (ALpharadin in SYMptomatic Prostate CAncer patients) study for bone metastases resulting from CRPC in 922 patients. [ 19 ]


The ALSYMPCA study was stopped early after a pre-planned efficacy interim analysis, following a recommendation from an Independent Data Monitoring Committee, on the basis of achieving a statistically significant improvement in overall survival (two-sided p-value = 0.0022, HR = 0.699, the median overall survival was 14.0 months for  223 Ra and 11.2 months for placebo). [ 19 ]  Earlier phase II of the trial showed a median increased survival of 18.9 weeks (around 4.4 months). [ 18 ]  The lower figure of 2.8 months increased survival in interim phase III results is a probable result of stopping the trial; median survival time for patients still alive could not be calculated. A 2014 update indicates a median increased survival of 3.6 months. [ 20 ]


In May 2013,  223 Ra received marketing approval from the US  Food and Drug Administration  (FDA) [ 21 ] [ 22 ]  as a treatment for CRPC with bone metastases in people with symptomatic bone metastases and without known visceral disease.  223 Ra received priority review as a treatment for an unmet medical need, based on its ability to extend overall survival as shown its Phase III trial. [ 21 ]


This study also led to approval in the  European Union  in November 2013, [ 12 ] [ 23 ]  The  European Medicines Agency  subsequently recommended restricting its use to patients who have had two previous treatments for metastatic prostate cancer or who cannot receive other treatments. The medicine must also not be used with  abiraterone acetate , prednisone or prednisolone and its use is not recommended in patients with a low number of osteoblastic bone metastases. [ 24 ]


223 Ra also showed promising preliminary results in a phase IIa trial enrolling 23 women with bone metastases resulting from  breast cancer  that no longer responds to  endocrine therapy . [ 25 ]   223 Ra treatment reduced the levels of bone  alkaline phosphatase  (bALP) and urine  N-telopeptide  (uNTX), key markers of bone turnover associated with bone metastases in breast cancer, diminished bone pain slightly though consistently, and was well tolerated. Another single-arm, open-label Phase II trial reported possible efficacy of  223 Ra combined with  endocrine therapy  in hormone-receptor-positive, bone-dominant breast cancer metastasis. [ 26 ]


The most common side effects reported during clinical trials in men receiving  223 Ra were nausea, diarrhea, vomiting and swelling of the leg, ankle or foot. The most common abnormalities detected during blood testing were  anemia ,  lymphocytopenia ,  leukopenia ,  thrombocytopenia  and  neutropenia . [ 21 ]


Although radium does not easily form stable molecular complexes, [ 27 ]  data has been presented on methods to increase and customize its specificity for particular cancers by linking it to  monoclonal antibodies , by enclosing the  223 Ra in  liposomes  bearing the antibodies on their surface. [ 28 ]


The side effects of radiotherapy on fertility  are a growing concern to patients undergoing radiotherapy as cancer treatments.  Radiotherapy  is essential for certain  cancer treatments  and often is the first point of call for patients. [ 1 ]   Radiation  can be divided into two categories:  ionising radiation (IR)  and  non-ionising radiation (NIR) . IR is more dangerous than NIR and a source of this radiation is X-rays used in medical procedures, for example in radiotherapy. [ 2 ]


IR can have varying impacts which depend on many factors including age,  irradiation field  and treatment dose and duration. Where the radiotherapy is directed is important as IR to the pelvis will affect the ovary and uterus or testis. Whereas cranial irradiation will disrupt the  hypothalamic-pituitary-gonadal axis  (HPG-A), causing subsequent disruption of hormone secretion. [ 1 ]


In females, IR can have long-term effects on  fertility , specifically on  ovarian insufficiency , pubertal arrest and subsequent  infertility . [ 1 ]


In males, the use of radiotherapy can disrupt the  endocrine system  leading to altered  spermatogenesis  and consequently a decrease in sperm count, sperm motility, sperm morphology and sperm viability. [ 2 ]


The rapid evolution of radiotherapy technologies has had the benefit of more effective and accurate treatments with less side effects. [ 3 ]


Radiation therapy can have a significant impact on female fertility. The damage induced varies greatly and is determined by factors such as the age of the patient along with the dose and duration of treatment given. [ 1 ]  Estimates suggest that less than 2Gy of radiation could destroy half of a female’s immature  oocytes . Female ovaries are estimated to store over 1,000,000  primordial follicles  at birth which decrease in number and quality with increasing age via processes such as  apoptosis . [ 1 ]  Radiation therapy greatly accelerates this decline. Permanent damage occurs with  follicular atrophy  and reduced follicle numbers. [ 1 ]  Consequently these changes lead to uterine dysfunction due to changes in ovarian hormone production which can result in  early menopause  and risk of infertility. [ 1 ]


Hormonal disruption includes female patients experiencing decrease  LH (luteinising hormone)  secretion and attenuated LH surges leading to increased risk of ovarian failure. LH plays an important role in proper sexual development. Further potential  endocrinopathies  include  hypogonadism  and  hyperprolactinemia . [ 4 ]  Studies now suggest that the stage of follicular development may determine how much damage is induced. [ 5 ]


Radiation therapy has been seen to also have a direct impact on the uterus, leading to changes to its vascular supply, volume and elasticity.  Necrosis , atrophy and fibrosis have also all been observed in the  endometrium  and  myometrium . Changes such as these have significant consequences in regard to pregnancy outcomes; studies suggest cancer patients receiving radiation have a higher chance of experiencing  miscarriages  or having low birth weight, premature children. [ 1 ]  The likelihood of  perinatal infant mortality  and low birth weight are significantly related to radiation dose. [ 4 ]


Male fertility can be greatly impacted by radiotherapy of the reproductive system. Spermatogenesis is a process by which male sperm cells are produced. [ 6 ]  This process can take up to 70 days to complete. Some of the cells involved in this process can be damaged by the use of radiotherapy. Cells called  spermatogonia  are the most heavily impacted by radiotherapy. [ 2 ]  These are the cells that go on to divide to produce  spermatozoa , or what are commonly known as sperm cells. Spermatogonia are the most impacted by radiotherapy because they are more radiosensitive than other types of cells such as spermatozoa. [ 2 ]  This means that the whole spermatogenic process is impacted by radiotherapy.


In addition to the damage of spermatogonia, the cells which produce a hormone called testosterone are also impaired by radiotherapy. [ 2 ]   Testosterone  is the main male hormone in the body. [ 7 ]  These cells are called  Leydig cells  and they are found in the  testes . However, Leydig cells are far more resistant to radiation than other cells in the testes and only become damaged by high levels of radiotherapy. [ 2 ]  These cells are more sensitive when the radiotherapy takes place in childhood. Damaged Leydig cells reduce the levels of testosterone in the body, which in turn increases the levels of another hormone called LH. [ 2 ]  Clinically, the monitoring of these two hormones can be indicative of Leydig cell function and health. [ 2 ]


In combination, these two processes can lead to male fertility being compromised and can sometimes result in infertility.


The number of childhood cancer survivors is increasing due to technological and diagnostic advancements. [ 8 ]  However as a result, there is increasing concern of the long-term effects of cancer treatments, such as radiotherapy treatment. A significant issue associated with childhood radiotherapy includes infertility. [ 8 ]


Prepubescent  males who experience radiotherapy to their testes, can result in reduced  spermatogenesis . [ 9 ]  This can be through damage to the  germ cells , the  sertoli cells  and/or  Leydig cells . [ 9 ]  Both the dosage and the timing of the treatment can determine the extent of disruption to spermatogenesis. In prepubescent males, low doses (>1-3Gy) can cause short-term  oligospermia  or  azoospermia , while higher doses (>2-3 Gy) can cause permanent azoospermia. [ 9 ]


Moreover, testicular radiation or  central nervous system  (CNS) radiation in prepubertal males can affect  testosterone  levels and cause hypoandrogenism. Testicular radiation damages the androgen-producing Leydig cells while CNS radiation impairs the hypothalamic-pituitary-gonadal (HPG) axis, reducing  gonadotropin  production. [ 9 ]


In prepubescent females, high radiation dose to the pelvic region can also have adverse side effects on fertility. Long-term effects include early onset  menopause , ovarian failure and inability to complete puberty. [ 10 ]  Where pregnancy occurs in these individuals, there are high risks associated with the health of the offspring due to pregnancy complications. These include low birth weight, miscarriage and premature labour. [ 10 ]


In modern medicine there are multiple options to limit the effect of cancer treatment on fertility.  One of the preventative measures in females is transposition of gonadal organs further from local therapeutic agents with a success rate over 90%. [ 11 ]  Another less invasive method used for many years is  lead shielding  of gonadal region in both males and females as a protective measure against radiotherapy. [ 5 ]


In prepubescent males novel techniques such as  testicular tissue extraction  and  cryopreservation  as well as  in vitro  maturation of spermatogonia which can then be transferred to native tissue after the treatment are being heavily researched. [ 5 ]  The most common solution is cryopreservation of sperms in post pubertal males and cryopreservation of oocytes or embryos for females with smaller age constrain compared to males who can then utilise multiple  assisted reproductive techniques  (ART) methods such as intrauterine insemination,  IVF  or ICSI as an alternative resource for preservation of fertility. [ 5 ]


Future approach to this problem focuses on cytoprotective strategies using hormonal treatment to alter HPG-A to guard reproductive organs from radiotherapy. By disrupting the  gametogenesis  or decreasing the sensitivity of germ cells scientists could acquire quiescent state less susceptible to side effects of cancer treatment. [ 12 ]


Sirtex Medical Limited  is a medical device firm that offers radioactive treatment for inoperable  liver cancer  called  SIR-Spheres   microspheres . [ 1 ]  Sirtex was founded in 1997 in Australia and today has offices and production facilities in the  U.S. ,  Australia ,  Germany , and  Singapore . Following its acquisition by  China Grand Pharmaceutical  and CDH Genetech, Sirtex delisted from the  Australian Securities Exchange  (ASX:SRX) on Monday, September 24, 2018.


The company is currently headed by Kevin R. Smith, who was appointed as CEO on October 16, 2019. [ 2 ]


When SIR-Sphere microspheres are used to treat liver cancer, the treatment is called  selective internal radiation therapy  (called SIRT). This is a relatively new treatment option for people suffering from  inoperable   liver cancer . [ 3 ]  SIR-Spheres are very small radioactive beads about one-third the size of a human hair that are injected into tumours within the liver.


The  radioactive  microspheres have a  half-life  of about 64 hours. They are administered by a trained interventional  radiologist  who specialises in minimally invasive, targeted treatments. The procedure is usually performed under local sedation. A small incision is made in the patient's groin, and a flexible  catheter  is guided into the  liver  through the  femoral artery  in the leg up to the tumour sites. The catheter is moved through the hepatic artery and positioned by the  interventional radiologist  to allow for targeted infusion of the SIR-Spheres microspheres to the site of the tumors. The microspheres take approximately 15 minutes to be infused, with the whole procedure taking about an hour. Most patients are discharged within 24 hours. [ 4 ]


Primary  liver cancer , also known as  hepatocellular carcinoma  (HCC), is the most frequent type of liver cancer, accounting for approximately 90% of the primary  malignant  liver tumours in adults. Liver cancer is the sixth most prevalent malignancy and the third greatest cause of cancer-related deaths worldwide. [ 5 ]  Every year, around 600,000 instances of liver cancer are diagnosed around the world. This includes around 19,000 in the US, 54,000 in Europe, and 390,000 in China, Korea, and Japan. The incidence of HCC is rising in Asia as chronic infection with Hepatitis B and C becomes more common. Additional risk factors include iron overload,  alcoholic cirrhosis  and some congenital disorders. Patients with liver cancer had a lower fiver-year survival rate than those with other cancer types. [ 6 ]


Colorectal cancer  (CRC), often known as  colon cancer  or large bowel cancer, is the third highest cause of cancer-related deaths in the western world. [ 7 ]  Each year, an estimated 1.6 million people are diagnosed with the condition around the world. An estimated 50% of CRC patients will develop liver  metastases . Sirtex targets metastatic colorectal cancer (mCRC) via SIR-Sphere microspheres. It has been thought that in 30-40% of individuals with severe illness, the liver is the only site of dissemination.


At presentation, 20-25% of patients will have clinically identifiable liver  metastases , and up to 50% of all patients develop liver metastases develop liver metastases within three years of primary tumor removal. [ 8 ]  On average, 25% of patients with metastatic liver disease are eligible for liver resection surgery, which is the only possible cure available to them. [ 9 ]  The remaining patients are eligible for alternative treatments such as  chemotherapy  and SIR-Sphere microspheres.


Sirtex is currently looking at new ways to treat other forms of cancer using the SIR-Spheres technology. This research is taking place at the  Australian National University  (ANU) and several institutions in the US and Europe. Sirtex is also working to develop a new technology that will help improve the treatment and survival of cancer patients. [ 10 ]  At present, this is focused on the three areas listed below.


Results from the largest, most comprehensive study to date evaluating SIRT in liver metastases from colorectal cancer were presented at ASCO in 2012, ASCO-GI 2013, and ASCO in 2014. The various subsets of the MORE study, led by Andrew S. Kennedy, M.D., Physician in Chief, Radiation Oncology, Sarah Cannon Research Institute, Nashville, Tenn., have demonstrated safety and efficacy as well as the same in treating the elderly. The most recent set of data presented at ASCO in 2014 documented the ability to predict the success of SIRT using standard laboratory tests prior to treatment. [ 11 ]


In addition, the global SIRFLOX study, which completed  patient recruitment  in 2013, will evaluate SIR-Sphere microspheres as a first-line treatment for colorectal liver metastases. [ 12 ]


SIR-Sphere microspheres [ 13 ]  are regulated as a medical device. The product was approved for sale in the US in March 2002. The US  Centers for Medicare and Medicaid Services  (CMS) currently reimburse SIR-Spheres microspheres under  Medicare  Code C2616. [ 14 ]


SIR-Spheres are covered in Australia by private insurers and reimbursed under  Medicare . [ 15 ]


In Europe, SIR-Sphere microspheres are regulated under the Active Implantable Medical Device Directive. The product received CE Mark approval in October 2002. [ 16 ]


In the UK, patients treated with SIR-Spheres were either self-funded, had private medical insurance, or had the microspheres donated by Sirtex. A small number have been approved by the  National Health Service  (NHS). [ citation needed ]  This is partly due to formal guidance documentation provided by the  National Institute for Clinical Excellence  (NICE), which questioned the clinical benefits of SIR-Sphere microspheres requiring patient consent. Since 2013, it has been mandatory for NHS organisations in the UK to provide funding for medicines and treatment as recommended by NICE. [ 17 ] [ 18 ]  A favourable review will see the  National Health Service  pay for treatment across the UK and help reimbursement in other EU countries.


On 3 September 2013, Sirtex announced that dose sales of SIR-Spheres microspheres grew a solid 21 percent, with more than 4,750 doses being supplied in the Americas for the year ending June 30, 2013. Globally, revenue was $100 million Australian dollars, up 16 percent from 2012, with a net profit after tax of AU$18 million. Dose sales of SIR-Spheres microspheres grew 19 percent in fiscal year 2013, with Asia Pacific reporting growth of 29 percent and Europe, the Middle East, and Africa increasing nine percent. Sirtex plans to triple manufacturing capacity in 2014 with new facilities in Germany and the U.S. [ 19 ]


Superficial X-rays  are low-energy  X-rays  that do not penetrate very far before they are absorbed. They are produced by  X-ray tubes  operating at  voltages  in the 10–100  kV  range, and therefore have peak energies in the 10–100  keV  range. [ 1 ]  The  Maximar-100  was a widely-adopted superficial radiation therapy unit.


Precise naming and definitions of energy ranges may vary, and X-rays at the lower end of this range may also be known as  Grenz rays . [ 2 ]  They are useful in  radiation therapy  for the treatment of various benign or malignant  skin  problems, including  skin cancer  and severe  eczema . [ 3 ] [ 4 ]  They have a useful depth of up to 5 mm. [ 2 ] [ 5 ]  In some locations, orthovoltage treatment is being replaced by  electron therapy  or  brachytherapy . [ 6 ]


As well as  teletherapy , X-rays in this energy range (and the low  orthovoltage  range) are used for  imaging  patients, to analyse materials and objects in  industrial radiography  and for  crystallography .


This  dermatology  article is a  stub . You can help Wikipedia by  expanding it .


Tissue-to-air ratio  (TAR) is a term used in  radiotherapy   treatment planning  to help calculate  absorbed dose  to water in conditions other than those directly measured.


The TAR at a point in a water phantom irradiated by a photon beam is taken to be the ratio of the total absorbed dose at that point to the absorbed dose at the same point in a minimal-scatter phantom with just-sufficient build-up. [ 1 ] [ 2 ]


Tissue-air ratio is defined as the ratio of the dose to water at a given depth to the dose in air measured with a buildup cap:


T
 A
 R
 =

 D
 (
 f
 ,
 z
 )

 D
 (
 f
 ,
 0
 )

 {\displaystyle TAR={{D(f,z)} \over {D(f,0)}}}


where D(f,z) is the dose at a given depth z and distance focus-detector f; and D(f,0) is the dose in air (z=0).


Measurements for each are taken using an  ion chamber  for identical source to detector distances and field sizes. [ 3 ]


Lynn D. Wilson  is an American radiation oncologist.  He is a professor of Therapeutic Radiology and of Dermatology, Executive Vice Chairman, Therapeutic Radiology, and Deputy Chief Medical Officer for Radiation Oncology Services at  Yale Cancer Center  and  Yale School of Medicine  in New Haven, Connecticut. [ 1 ] [ 2 ]  In 2011, Wilson was named a Fellow of the  American Society for Radiation Oncology  (FASTRO). [ 3 ]


Wilson earned his medical degree at  George Washington University School of Medicine  in Washington, D.C., before completing a residency in radiation oncology at  Yale New Haven Hospital ; he served as a chief resident before joining the Yale School of Medicine faculty in 1994. [ 4 ]  Prior to his medical degree, Wilson received a master in public health degree, focusing on health services administration, at Yale School of Medicine. [ 5 ]


Wilson worked in the laboratory of James B. Mitchell, within the Radiation Biology Branch of the  National Cancer Institute / National Institutes of Health  (NIH) [ 6 ]  where he also collaborated with former Commissioner of  Food and Drugs   Stephen Hahn  on journal articles. [ 7 ]


Wilson cares for patients with cutaneous lymphoma and breast cancer. His research focus is on outcomes and treatment-related factors for patients receiving radiation for cutaneous lymphoma and has published on radiation therapy for lung cancer as well as on breast cancer. [ 8 ]  Wilson has served as the director for clinical affairs in the Department of Therapeutic Radiology at Yale since in 2005 [ 9 ]  and was the residency training program director between 2004 and 2013. [ 6 ]


From 2011 to 2018, Wilson served on the board of trustees for the  American Board of Radiology [ 10 ]  and was a member of the American Society for Radiation Oncology board of directors from 2016 to 2020. [ 11 ]


Wilson and his wife Nancy were married in 1997 and have two children. [ 13 ]


Wilson is a former race car driver, having raced in the Rolex 24 at Daytona three times (2001, 2002, 2004). In 2001, as part of team Autometrics, Wilson and three other drivers took 23rd place overall and 13th in class after starting 75th overall. The 2001 race was the last time an air-cooled Porsche 911 ever raced in the famed Rolex 24 hours at Daytona. The Autometrics car (#14), was the only air-cooled Porsche 911 in the GT class in the 2001 race. [ 14 ]


In 2020 Wilson received the Anthony Edward Kupka ’64 Distinguished Alumnus Award from the  Landon School . [ 15 ]


In 2008, Wilson received the inaugural  David J. Leffell , MD Prize for Clinical Excellence [ 16 ]  and in the same year was the recipient of the  Francis Gilman Blake  Award for teaching at Yale School of Medicine. [ 17 ]


Radiography  is an  imaging technique  using  X-rays ,  gamma rays , or similar ionizing radiation and non-ionizing radiation to view the internal form of an object. Applications of radiography include medical  ("diagnostic" radiography and "therapeutic radiography") and  industrial radiography . Similar techniques are used in  airport security , (where "body scanners" generally use  backscatter X-ray ). To create an image in  conventional radiography , a beam of X-rays is produced by an  X-ray generator  and it is projected towards the object. A certain amount of the X-rays or other radiation are absorbed by the object, dependent on the object's density and structural composition. The X-rays that pass through the object are captured behind the object by a  detector  (either  photographic film  or a digital detector). The generation of flat  two-dimensional  images by this technique is called  projectional radiography . In  computed tomography  (CT scanning), an X-ray source and its associated detectors rotate around the subject, which itself moves through the conical X-ray beam produced. Any given point within the subject is crossed from many directions by many different beams at different times. Information regarding the attenuation of these beams is collated and subjected to computation to generate two-dimensional images on three planes (axial, coronal, and sagittal) which can be further processed to produce a three-dimensional image.


Radiography's origins and  fluoroscopy's origins  can both be traced to 8 November 1895, when German physics professor  Wilhelm Conrad Röntgen  discovered the X-ray and noted that, while it could pass through human tissue, it could not pass through bone or metal. [ 1 ]  Röntgen referred to the radiation as "X", to indicate that it was an unknown type of radiation. He received the first  Nobel Prize in Physics  for his discovery. [ 2 ]


There are conflicting accounts of his discovery because Röntgen had his lab notes burned after his death, but this is a likely reconstruction by his biographers: [ 3 ] [ 4 ]  Röntgen was investigating  cathode rays  using a  fluorescent  screen painted with barium  platinocyanide  and a  Crookes tube  which he had wrapped in black cardboard to shield its fluorescent glow. He noticed a faint green glow from the screen, about 1 metre away. Röntgen realized some invisible rays coming from the tube were passing through the cardboard to make the screen glow: they were passing through an opaque object to affect the film behind it. [ 5 ]


Röntgen discovered X-rays' medical use when he made a picture of his wife's hand on a photographic plate formed due to X-rays. The photograph of his wife's hand was the first ever photograph of a human body part using X-rays. When she saw the picture, she said, "I have seen my death." [ 5 ]


The first use of X-rays under clinical conditions was by  John Hall-Edwards  in  Birmingham, England , on 11 January 1896, when he radiographed a needle stuck in the hand of an associate. On 14 February 1896, Hall-Edwards also became the first to use X-rays in a  surgical operation . [ 6 ]


The United States saw its first medical X-ray obtained using a  discharge tube  of  Ivan Pulyui 's design. In January 1896, on reading of Röntgen's discovery, Frank Austin of  Dartmouth College  tested all of the discharge tubes in the physics laboratory and found that only the Pulyui tube produced X-rays. This was a result of Pulyui's inclusion of an oblique "target" of  mica , used for holding samples of  fluorescent  material, within the tube. On 3 February 1896 Gilman Frost, professor of medicine at the college, and his brother Edwin Frost, professor of physics, exposed the wrist of Eddie McCarthy, whom Gilman had treated some weeks earlier for a fracture, to the X-rays and collected the resulting image of the broken bone on  gelatin photographic plates  obtained from Howard Langill, a local photographer also interested in Röntgen's work. [ 7 ]


X-rays were put to diagnostic use very early; for example,  Alan Archibald Campbell-Swinton  opened a radiographic laboratory in the United Kingdom in 1896, before the dangers of ionizing radiation were discovered. Indeed,  Marie Curie  pushed for radiography to be used to treat wounded soldiers in World War I. Initially, many kinds of staff conducted radiography in hospitals, including physicists, photographers, physicians, nurses, and engineers. The medical speciality of radiology grew up over many years around the new technology. When new diagnostic tests were developed, it was natural for the  radiographers  to be trained in and to adopt this new technology. Radiographers now perform  fluoroscopy ,  computed tomography ,  mammography ,  ultrasound ,  nuclear medicine  and  magnetic resonance imaging  as well. Although a nonspecialist dictionary might define radiography quite narrowly as "taking X-ray images", this has long been only part of the work of "X-ray departments", radiographers, and radiologists. Initially, radiographs were known as roentgenograms, [ 8 ]  while  skiagrapher  (from the  Ancient Greek  words for "shadow" and "writer") was used until about 1918 to mean  radiographer .  The Japanese term for the radiograph,  rentogen  ( レントゲン ) , shares its etymology with the original English term.


Since the body is made up of various substances with differing densities, ionising and non-ionising radiation can be used to reveal the internal structure of the body on an image receptor by highlighting these differences using  attenuation , or in the case of ionising radiation, the absorption of X-ray  photons  by the denser substances (like  calcium -rich bones). The discipline involving the study of anatomy through the use of radiographic images is known as  radiographic anatomy . Medical radiography acquisition is generally carried out by  radiographers , while image analysis is generally done by  radiologists . Some radiographers also specialise in image interpretation. Medical radiography includes a range of modalities producing many different types of image, each of which has a different clinical application.


The creation of images by exposing an object to  X-rays  or other high-energy forms of  electromagnetic radiation  and capturing the resulting remnant beam (or "shadow") as a latent image is known as "projection radiography".  The "shadow" may be converted to light using a fluorescent screen, which is then captured on  photographic film , it may be captured by a phosphor screen to be "read" later by a laser (CR), or it may directly activate a matrix of  solid-state  detectors (DR—similar to a very large version of a  CCD  in a digital camera).  Bone  and some organs (such as  lungs ) especially lend themselves to projection radiography. It is a relatively low-cost investigation with a high  diagnostic  yield. The difference between  soft  and  hard  body parts stems mostly from the fact that carbon has a very low X-ray cross section compared to calcium.


Computed tomography  or CT scan (previously known as CAT scan, the "A" standing for "axial") uses ionizing radiation (x-ray radiation) in conjunction with a computer to create images of both soft and hard tissues. These images look as though the patient was sliced like bread (thus, "tomography" – "tomo" means "slice"). Though CT uses a higher amount of ionizing x-radiation than diagnostic x-rays (both utilising X-ray radiation), with advances in technology, levels of CT radiation dose and scan times have reduced. [ 9 ]  CT exams are generally short, most lasting only as long as a breath-hold,  Contrast agents  are also often used, depending on the tissues needing to be seen. Radiographers perform these examinations, sometimes in conjunction with a radiologist (for instance, when a radiologist performs a CT-guided  biopsy ).


DEXA , or bone densitometry, is used primarily for  osteoporosis  tests. It is not projection radiography, as the X-rays are emitted in two narrow beams that are scanned across the patient, 90 degrees from each other. Usually the hip (head of the  femur ), lower back ( lumbar spine ), or heel ( calcaneum ) are imaged, and the bone density (amount of calcium) is determined and given a number (a T-score).  It is not used for bone imaging, as the image quality is not good enough to make an accurate diagnostic image for fractures, inflammation, etc. It can also be used to measure total body fat, though this is not common. The radiation dose received from  DEXA scans  is very low, much lower than projection radiography examinations. [ citation needed ]


Fluoroscopy  is a term invented by  Thomas Edison  during his early X-ray studies.  The name refers to the fluorescence he saw while looking at a glowing plate bombarded with X-rays. [ 10 ]


The technique provides moving projection radiographs. Fluoroscopy is mainly performed to view movement (of tissue or a contrast agent), or to guide a medical intervention, such as angioplasty, pacemaker insertion, or joint repair/replacement. The last can often be carried out in the operating theatre, using a portable fluoroscopy machine called a C-arm. [ 11 ]   It can move around the surgery table and make digital images for the surgeon. Biplanar Fluoroscopy works the same as single plane fluoroscopy except displaying two planes at the same time. The ability to work in two planes is important for orthopedic and spinal surgery and can reduce operating times by eliminating re-positioning. [ 12 ]


Angiography  is the use of fluoroscopy to view the cardiovascular system. An iodine-based contrast is injected into the bloodstream and watched as it travels around.  Since liquid blood and the vessels are not very dense, a contrast with high density (like the large iodine atoms) is used to view the vessels under X-ray. Angiography is used to find  aneurysms , leaks, blockages ( thromboses ), new vessel growth, and placement of catheters and stents.  Balloon angioplasty  is often done with angiography.


Contrast radiography uses a radiocontrast agent, a type of  contrast medium , to make the structures of interest stand out visually from their background. Contrast agents are required in conventional  angiography , and can be used in both  projectional radiography  and  computed tomography  (called  contrast CT ). [ 13 ] [ 14 ]


Although not technically radiographic techniques due to not using X-rays, imaging modalities such as  PET  and  MRI  are sometimes grouped in radiography because the  radiology  department of hospitals handle all forms of  imaging . Treatment using radiation is known as  radiotherapy .


Industrial radiography  is a method of  non-destructive testing  where many types of manufactured components can be examined to verify the internal structure and integrity of the specimen.  Industrial Radiography can be performed utilizing either  X-rays  or  gamma rays .  Both are forms of  electromagnetic radiation .  The difference between various forms of electromagnetic energy is related to the  wavelength .  X and gamma rays have the shortest wavelength and this property leads to the ability to penetrate, travel through, and exit various materials such as  carbon steel  and other metals. Specific methods include  industrial computed tomography .


Image quality will depend on resolution and density.
Resolution is the ability an image to show closely spaced structure in the object as separate entities in the  image while density is the blackening power of the image.
Sharpness of a radiographic image is strongly determined by the size of the X-ray source. This is determined by the area of the electron beam hitting the anode.
A large photon source results in more blurring in the final image and is worsened by an increase in image formation distance. This blurring can be measured as a contribution to the  modulation transfer function  of the imaging system.


The dosage of radiation applied in radiography varies by procedure. For example, the effective dosage of a chest x-ray is 0.1 mSv, while an abdominal CT is 10 mSv. [ 15 ]  The  American Association of Physicists in Medicine  (AAPM) have stated that the "risks of medical imaging at patient doses below 50 mSv for single procedures or 100 mSv for multiple procedures over short time periods are too low to be detectable and may be nonexistent." Other scientific bodies sharing this conclusion include the  International Organization of Medical Physicists , the  UN Scientific Committee on the Effects of Atomic Radiation , and the  International Commission on Radiological Protection . Nonetheless, radiological organizations, including the  Radiological Society of North America  (RSNA) and the  American College of Radiology  (ACR), as well as multiple government agencies, indicate safety standards to ensure that radiation dosage is as low as possible. [ 16 ]


Lead  is the most common shield against X-rays because of its high density (11,340 kg/m 3 ), stopping power, ease of installation and low cost. The maximum range of a high-energy photon such as an X-ray in matter is infinite; at every point in the matter traversed by the photon, there is a probability of interaction. Thus there is a very small probability of no interaction over very large distances. The shielding of photon beam is therefore exponential (with an  attenuation length  being close to the  radiation length  of the material); doubling the thickness of shielding will square the shielding effect.


Table in this section shows the recommended thickness of lead shielding in function of X-ray energy, from the Recommendations by the Second International Congress of Radiology. [ 17 ]


In response to increased concern by the public over radiation doses and the ongoing progress of best practices, The Alliance for Radiation Safety in Pediatric Imaging was formed within the  Society for Pediatric Radiology . In concert with the  American Society of Radiologic Technologists , the  American College of Radiology , and the  American Association of Physicists in Medicine , the Society for Pediatric Radiology developed and launched the Image Gently campaign which is designed to maintain high quality imaging studies while using the lowest doses and best radiation safety practices available on pediatric patients. [ 18 ]  This initiative has been endorsed and applied by a growing list of various professional medical organizations around the world and has received support and assistance from companies that manufacture equipment used in radiology.


Following upon the success of the Image Gently campaign, the American College of Radiology, the Radiological Society of North America, the American Association of Physicists in Medicine, and the American Society of Radiologic Technologists have launched a similar campaign to address this issue in the adult population called Image Wisely. [ 19 ]  The  World Health Organization  and  International Atomic Energy Agency  (IAEA) of the United Nations have also been working in this area and have ongoing projects designed to broaden best practices and lower patient radiation dose. [ 20 ] [ 21 ] [ 22 ]


Contrary to advice that emphasises only conducting radiographs when in the patient's interest, recent evidence suggests that they are used more frequently when dentists are paid under fee-for-service. [ 23 ]


In medicine and dentistry,  projectional radiography  and  computed tomography images  generally use X-rays created by  X-ray generators , which generate X-rays from  X-ray tubes .  The resultant images from the radiograph (X-ray generator/machine) or CT scanner are correctly referred to as "radiograms"/"roentgenograms" and "tomograms" respectively.


A number of other sources of  X-ray   photons  are possible, and may be used in industrial radiography or research; these include  betatrons ,  linear accelerators  (linacs), and  synchrotrons . For  gamma rays ,  radioactive  sources such as  192 Ir ,  60 Co , or  137 Cs  are used.


An  anti-scatter grid  may be placed between the patient and the detector to reduce the quantity of scattered x-rays that reach the detector. This improves the contrast resolution of the image, but also increases radiation exposure for the patient. [ 24 ]


Detectors can be divided into two major categories: imaging detectors (such as  photographic plates  and X-ray film ( photographic film ), now mostly replaced by various  digitizing  devices like  image plates  or  flat panel detectors ) and dose measurement devices (such as  ionization chambers ,  Geiger counters , and  dosimeters  used to measure the local  radiation exposure ,  dose , and/or dose rate, for example, for verifying that  radiation protection  equipment and procedures are effective on an ongoing basis). [ 25 ] [ 26 ] [ 27 ]


A radiopaque anatomical side marker is added to each image. For example, if the patient has their right hand x-rayed, the radiographer includes a radiopaque "R" marker within the field of the x-ray beam as an indicator of which hand has been imaged. If a physical marker is not included, the radiographer may add the correct side marker later as part of digital post-processing. [ 28 ]


As an alternative to X-ray detectors,  image intensifiers  are analog devices that readily convert the acquired X-ray image into one visible on a video screen. This device is made of a vacuum tube with a wide input surface coated on the inside with  caesium iodide  (CsI). When hit by X-rays, phosphor material causes the  photocathode  adjacent to it to emit electrons. These electrons are then focused using electron lenses inside the intensifier to an output screen coated with phosphorescent materials. The image from the output can then be recorded via a camera and displayed. [ 29 ]


Digital devices known as array detectors are becoming more common in fluoroscopy. These devices are made of discrete pixelated detectors known as  thin-film transistors  (TFT) which can either work  indirectly  by using photo detectors that detect light emitted from a scintillator material such as CsI, or  directly  by capturing the electrons produced when the X-rays hit the detector. Direct detectors do not tend to experience the blurring or spreading effect caused by phosphorescent scintillators or by film screens since the detectors are activated directly by X-ray photons. [ 30 ]


Dual-energy  radiography  is where images are acquired using two separate  tube voltages . This is the standard method for  bone densitometry . It is also used in  CT pulmonary angiography  to decrease the required dose of  iodinated contrast . [ 31 ]


The  algebraic reconstruction technique  ( ART ) is an  iterative reconstruction  technique used in  computed tomography . It reconstructs an image from a series of angular projections (a  sinogram ).  Gordon , Bender and  Herman  first showed its use in image reconstruction; [ 1 ]  whereas the method is known as  Kaczmarz method  in numerical linear algebra. [ 2 ] [ 3 ]


An advantage of ART over other reconstruction methods (such as  filtered backprojection ) is that it is relatively easy to incorporate prior knowledge into the reconstruction process.


ART can be considered as an iterative solver of a system of linear equations

 A
 x
 =
 b

 {\displaystyle Ax=b}

 , where:


Given a real or complex matrix

 A

 {\displaystyle A}

  and a real or complex vector

 b

 {\displaystyle b}

 , respectively, the method computes an approximation of the solution of the linear systems of equations as in the following formula,


where

 i
 =
 k

 mod

 m

 +
 1

 {\displaystyle i=k{\bmod {m}}+1}

 ,

 a

 i

 {\displaystyle a_{i}}

  is the  i -th row of the matrix

 A

 {\displaystyle A}

 ,

 b

 i

 {\displaystyle b_{i}}

  is the  i -th component of the vector

 b

 {\displaystyle b}

 .


λ

 k

 {\displaystyle \lambda _{k}}

  is an optional relaxation parameter, of the range

 0
 <

 λ

 k

 ≤
 1

 {\displaystyle 0<\lambda _{k}\leq 1}

 . The relaxation parameter is used to slow the convergence of the system. This increases computation time, but can improve the  signal-to-noise ratio  of the output. In some implementations, the value of

 λ

 k

 {\displaystyle \lambda _{k}}

  is reduced with each successive iteration. [ 4 ]


A further development of the ART algorithm is the  simultaneous algebraic reconstruction technique  (SART) algorithm.


This  computer science  article is a  stub . You can help Wikipedia by  expanding it .


Automatic Exposure Control  (AEC) is an  X-ray  exposure termination device.  A  medical radiographic  exposure is always initiated by a human operator but an AEC detector system may be used to terminate the exposure when a predetermined amount of radiation has been received. [ 1 ]  The intention of AEC is to provide consistent x-ray image exposure, whether to film, a digital  detector  or a  CT scanner . AEC systems may also automatically set exposure factors such as the  X-ray tube  current and voltage in a CT. [ 2 ]


In  projectional radiography  an AEC system uses one or more physically thin radiation  ionization chambers  (the "AEC detector") which is positioned between the X-ray source and the x-ray receptor. Where low energy x-rays are used such as in  mammography  the AEC detector is placed behind the image receptor to avoid creating a shadow. [ 3 ] : 106


In early radiographic AEC systems, a large paddle (17" x 17") of transparent lucite was sandwiched between rare earth screens, [ 4 ]  which emitted photons when excited by X-rays. The individual lucite sections were open on one end, and a solenoid was used to select one of three, or a combination of shutters that allowed the generated light into a  Photomultiplier tube . The output of the PMT was then converted to a signal, which ramped in the positive direction until a preprogrammed threshold was reached. At this point, the X-ray generator terminated the exposure. This method is no longer used, and has been replaced by the iontomat.
In an iontomat, a weak ionization signal resulting from the radiographic X-rays passing through it are  integrated  as a ramp shaped  voltage   waveform .  This ramp signal rises until it matches a pre-set threshold. At this point the x-ray exposure is terminated by the X-ray generator. [ 5 ]
AEC devices are calibrated to ensure that similar exams have linearity in  optical density . [ 6 ]


Modern computed tomography (CT) scanners have AEC systems which aim to maintain image quality for patients of varying sizes, whilst keeping doses  as low as reasonably practicable . The systems are also designed to maintain quality with the varying size and  attenuation  of an individual patient over their length. Implementations vary between manufacturers, some systems are based on a desired  noise  level in the image, while others are based on a specified reference output (milliampere second,  mAs ). [ 7 ] [ 8 ]


CT AEC systems use the initial "scanogram", a fixed angle planning view, to determine the relative size of the patient, and variation over their length. The  tube  output is then adjusted for overall size. The output is also typically modulated for each rotation in response to changes in attenuation over patient length. Some systems adjust output during each rotation, which is known as rotational modulation, based on measured attenuation in the previous rotation. [ 9 ]


Because patients vary in size and shape, an AEC device is very useful in achieving consistent x-ray film densities, which can be difficult when manually setting exposure factors without AEC. [ 3 ] : 130


AEC devices are susceptible to operator error (usually due to mispositioned  anatomy  or having the incorrect AEC chamber selected). [ 10 ]   Prosthetic  devices such as total hip hardware can also cause the selected ionization chamber to overexpose the image receptor. This is due to the absorption of the X-ray beam into the metal of the hardware as opposed to exposing the ionization chamber. [ 11 ]


An  autoradiograph  is an image on an  X-ray  film or  nuclear emulsion  produced by the pattern of decay emissions (e.g.,  beta particles  or  gamma rays ) from a distribution of a  radioactive  substance. Alternatively, the autoradiograph is also available as a digital image (digital autoradiography), due to the recent development of  scintillation  gas detectors [ 1 ]  or rare-earth phosphorimaging systems. [ 2 ]  The film or emulsion is apposed to the labeled tissue section to obtain the autoradiograph (also called an autoradiogram).  The  auto-  prefix indicates that the radioactive substance is within the sample, as distinguished from the case of  historadiography  or microradiography, in which the sample is marked using an external source. Some autoradiographs can be examined microscopically for localization of silver grains (such as on the interiors or exteriors of cells or organelles) in which the process is termed micro-autoradiography. For example, micro-autoradiography was used to examine whether  atrazine  was being metabolized by the  hornwort  plant or by  epiphytic   microorganisms  in the  biofilm  layer surrounding the plant. [ 3 ]


In  biology , this technique may be used to determine the tissue (or cell) localization of a radioactive substance, either introduced into a metabolic pathway, bound to a receptor [ 4 ] [ 5 ]  or enzyme, or hybridized to a nucleic acid. [ 6 ]  Applications for autoradiography are broad, ranging from biomedical to environmental sciences to industry.


The use of  radiolabeled ligands  to determine the tissue distributions of receptors is termed either  in vivo  or  in vitro   receptor autoradiography  if the ligand is administered into the circulation (with subsequent tissue removal and sectioning) or applied to the tissue sections, respectively. [ 7 ]  Once the receptor density is known,  in vitro  autoradiography can also be used to determine the anatomical distribution and affinity of a radiolabeled drug towards the receptor. For  in vitro  autoradiography, radioligand was directly applying on frozen tissue sections without administration to the subject. Thus it cannot follow the distribution, metabolism and degradation situation completely in the living body. But because target in the cryosections is widely exposed and can direct contact with radioligand,  in vitro  autoradiography is still a quick and easy method to screen drug candidates,  PET  and  SPECT  ligands. The ligands are generally labeled with  3 H ( tritium ),  18 F ( fluorine ),  11 C ( carbon ) or  125 I  ( radioiodine ). Compare to  in vitro ,  ex vivo  autoradiography were performed after administration of radioligand in the body, which can decrease the artifacts and are closer to the inner environment.


The distribution of RNA transcripts in tissue sections by the use of radiolabeled, complementary oligonucleotides or ribonucleic acids ("riboprobes") is called  in situ hybridization histochemistry . Radioactive precursors of DNA and RNA, [ 3 H]- thymidine  and [ 3 H]- uridine  respectively, may be introduced to living cells to determine the timing of several phases of the cell cycle. RNA or DNA viral sequences can also be located in this fashion. These probes are usually labeled with  32 P,  33 P, or  35 S.  In the realm of behavioral endocrinology, autoradiography can be used to determine hormonal uptake and indicate receptor location; an animal can be injected with a radiolabeled hormone, or the study can be conducted  in vitro .


The rate of DNA replication in a mouse cell growing  in vitro  was measured by autoradiography as 33 nucleotides per second. [ 8 ]   The rate of  phage T4  DNA elongation in phage-infected  E. coli  was also measured by autoradiography as 749 nucleotides per second during the period of exponential DNA increase at 37 °C (99 °F). [ 9 ]


Phosphorylation  means the posttranslational addition of a  phosphate group  to specific amino acids of proteins, and such modification can lead to a drastic change in the stability or the function of a protein in the cell. Protein phosphorylation can be detected on an autoradiograph, after incubating the protein in vitro with the appropriate  kinase  and γ-32P-ATP. The radiolabeled phosphate of latter is incorporated into the protein which is isolated via  SDS-PAGE  and visualized on an autoradiograph of the gel. (See figure 3. of a recent study showing that  CREB-binding protein  is phosphorylated by  HIPK2 . [ 10 ] )


In  plant physiology , autoradiography can be used to determine sugar accumulation in leaf tissue. [ 11 ]  Sugar accumulation, as it relates to autoradiography, can described the  phloem-loading strategy  used in a plant. [ 12 ]  For example, if sugars accumulate in the  minor veins  of a leaf, it is expected that the leaves have few  plasmodesmatal  connections which is indicative of  apoplastic  movement, or an active phloem-loading strategy. Sugars, such as  sucrose ,  fructose , or  mannitol , are  radiolabeled  with [ 14-C ], and then absorbed into leaf tissue by simple  diffusion . [ 13 ]  The leaf tissue is then exposed to autoradiographic film (or emulsion) to produce an image. Images will show distinct vein patterns if sugar accumulation is concentrated in leaf veins (apoplastic movement), or images will show a static-like pattern if sugar accumulation is uniform throughout the leaf ( symplastic  movement).


This autoradiographic approach contrasts to techniques such as  PET  and  SPECT  where the exact 3-dimensional localization of the radiation source is provided by careful use of coincidence counting, gamma counters and other devices.


Krypton-85  is used to inspect aircraft components for small defects. Krypton-85 is allowed to penetrate small cracks, and then its
presence is detected by autoradiography. The method is called "krypton gas penetrant imaging". The gas penetrates smaller openings than the liquids used in  dye penetrant inspection  and  fluorescent penetrant inspection . [ 14 ]


The task of radioactive decontamination following the  Baker  nuclear test at  Bikini Atoll  during  Operation Crossroads  in 1946 was far more difficult than the U.S. Navy had prepared for. Though the task's futility became apparent and the danger to cleanup crews mounted, Colonel  Stafford Warren , in charge of radiation safety, had difficulty persuading Vice Admiral  William H. P. Blandy  to abandon the cleanup and with it the surviving target ships. On August 10, Warren showed Blandy an autoradiograph made by a  surgeonfish  from the lagoon that was left on a photographic plate overnight. The film was exposed by alpha radiation produced from the fish's scales, evidence that plutonium, mimicking calcium, had been distributed throughout the fish. Blandy promptly ordered that all further decontamination work be discontinued. Warren wrote home, "A self X ray of a fish ... did the trick." [ 15 ]


Original publication by sole inventor
 Askins, Barbara S.  (1 November 1976). "Photographic image intensification by autoradiography". Applied Optics. 15 (11): 2860–2865. Bibcode:1976ApOpt..15.2860A. doi:10.1364/ao.15.002860.


Backscatter X-ray  is an advanced  X-ray imaging  technology. Traditional  X-ray machines  detect hard and soft materials by the variation in  x-ray  intensity transmitted through the target. In contrast, backscatter X-ray detects the radiation that  reflects  from the target. It has potential applications where less-destructive examination is required, and can operate even if only one side of the target is available for examination.


The technology is one of two types of whole-body imaging technologies that have been used to perform  full-body scans  of airline passengers to detect hidden weapons, tools, liquids, narcotics, currency, and other contraband. A competing technology is  millimeter wave scanner . One can refer to an  airport security  machine of this type as a "body scanner", "whole body imager (WBI)", "security scanner" or "naked scanner". [ 2 ]


In the United States, the FAA Modernization and Reform Act of 2012 required that all full-body scanners operated in airports by the  Transportation Security Administration  use "Automated Target Recognition" software, which replaces the picture of a nude body with the cartoon-like representation. [ 3 ]   As a result of this law, all backscatter X-ray machines formerly in use by the Transportation Security Administration were removed from airports by May 2013, since the agency said the vendor ( Rapiscan ) did not meet their contractual deadline to implement the software. [ 4 ]


In the European Union, backscatter X-ray screening of airline passengers was banned in 2012 to protect passenger safety. [ 5 ]


Backscatter technology is based on the  Compton scattering  effect of  X-rays , a form of  ionizing radiation . Unlike a traditional X-ray machine, which relies on the transmission of X-rays through the object, backscatter X-ray detects the radiation that reflects from the object and forms an image. The backscatter pattern is dependent on the material property and is good for imaging organic material.


In contrast to  millimeter wave scanners , which create a 3D image, backscatter X-ray scanners will typically only create a 2D image. For airport screening, images are taken from both sides of the human body. [ 6 ]


Backscatter X-ray was first applied in a commercial low-dose personnel scanning system by Dr. Steven W. Smith. [ 7 ] [ 8 ] [ 9 ]  Smith developed the Secure 1000 whole-body scanner in 1992 and then sold the device and associated patents to Rapiscan Systems, who now manufactures and distributes the device.


Some backscatter X-ray scanners can scan much larger objects, such as trucks and containers. This scan is much faster than a physical search and could potentially allow a larger percentage of shipping to be checked for smuggled items, weapons, drugs, or people.


There are also  gamma-ray -based systems coming to market. [ 10 ]


In May 2011, the  Electronic Privacy Information Center  filed suit against the  United States Department of Homeland Security  (DHS) under the  Freedom of Information Act , claiming that DHS had withheld nearly 1000 pages of documents related to the Z backscatter vans and other mobile backscatter devices. [ 11 ]


Since in addition to weapons, these machines are designed to be capable of detecting drugs, currency and contraband, which have no direct effect on airport security and passenger safety, some have argued that the use of these full body scanners is a violation of the  Fourth Amendment to the United States Constitution  and can be construed as an illegal search and seizure. [ 12 ]


Backscatter x-ray technology has been proposed as an alternative to personal searches at airport and other security checkpoints easily penetrating clothing to reveal concealed weapons. It raises privacy concerns about what is seen by the person viewing the scan. Some [ who? ]  worry that viewing the image violates confidential medical information, such as the fact a passenger uses a  colostomy bag , has a missing limb or wears a prosthesis, or is transgender.


The  ACLU  and the  Electronic Privacy Information Center  are opposed to this use of the technology. The ACLU refers to backscatter x-rays as a "virtual strip search". [ 13 ]  According to the  Transportation Security Administration  (TSA), in one trial 79 percent of the public opted to try backscatter over the traditional pat-down in secondary screening. [ 14 ]


It is "possible for backscatter X-raying to produce photo-quality images of what's going on beneath our clothes", thus, many software implementations of the scan have been designed to distort private areas. [ 15 ]  According to the TSA, further distortion is used in the Phoenix airport's trial system where photo-quality images are replaced by chalk outlines. [ 16 ] [ 17 ]  In light of this, some journalists have expressed concern that this blurring may allow people to carry weapons or certain explosives aboard by attaching the object or substance to their genitals. [ 15 ] [ 18 ]


The British newspaper  The Guardian  has revealed concern among British officials that the use of such scanners to scan children may be illegal under the  Protection of Children Act 1978 , which prohibits the creation and distribution of indecent images of children. This concern may delay the introduction of routine backscatter scanning in UK airports, which had been planned in response to the attempted Christmas Day 2009 attack on  Northwest Airlines Flight 253 . [ 19 ]


The  Fiqh Council of North America  have also issued the following  fatwa  in relation to full-body scanners:


It is a violation of clear Islamic teachings that men or women be seen naked by other men and women. Islam highly emphasizes haya (modesty) and considers it part of faith. The Quran has commanded the believers, both men and women, to cover their private parts. [ 20 ]


In August 2010, it was reported [ 21 ] [ who? ]  that U.S. Marshals (part of the Department of Justice), [ 22 ]  saved thousands of images from a low resolution  mm wave scanner : This machine does not show details of human anatomy, and is a different kind of machine from the one used in airports. TSA, part of the Department of Homeland Security, said that its scanners do not save images and that the scanners do not have the capability to save images when they are installed in airports, [ 23 ]  but later admitted that the scanners are required to be capable of saving images for the purpose of evaluation, training and testing. [ 24 ] [ 25 ]


Unlike cell phone signals, or millimeter-wave scanners, the energy being emitted by a backscatter X-ray is a type of  ionizing radiation  that breaks chemical bonds. Ionizing radiation is considered carcinogenic  even in very small doses  but at the doses used in airport scanners this effect is believed to be negligible for an individual. [ 26 ] [ 27 ] [ 28 ] [ 29 ]  If 1 million people were exposed to 520 scans in one year, one study estimated that roughly four additional cancers would occur due to the scanner, in contrast to the 600 additional cancers that would occur from the higher levels of radiation during flight. [ 30 ]


Since the scanners do not have a medical purpose, the United States  Food and Drug Administration  (FDA) does not need to subject them to the same safety evaluations as medical X-rays. [ 31 ]   However, the FDA has created a webpage comparing known estimates of the radiation from backscatter X-ray body scanners to that of other known sources, which cites various reasons they deem the technology to be safe. [ 32 ]


Four professors at the  University of California, San Francisco , among them members of NAS and an expert in cancer and imaging, in an April 2010 letter [ 33 ]  to the  presidential science and technology advisor  raised several concerns about the validity of the indirect comparisons the  Food and Drug Administration  used in evaluating the safety of backscatter x-ray machines. [ 34 ]  They argued that the effective dose is higher than claimed by the TSA and the body scanner manufacturers because the dose was calculated as if distributed throughout the whole body, whereas most of the radiation is absorbed in the skin and tissues immediately underneath. Other professors from the radiology department at UCSF disagree with the claims of the signing four professors. [ 35 ]


The UCSF professors requested that additional data be made public detailing the specific data regarding sensitive areas, such as the skin and certain organs, as well as data on the special (high-risk) population. In October 2010, the FDA and TSA responded to these concerns. [ 36 ] [ 37 ]  The letter cites reports which show that the specific dose to the skin is some 89,000 times lower than the annual limit to the skin established by the  NCRP . Regarding the UCSF concerns over the high-risk population to sensitive organs, the letter states that such an individual "would have to receive more than 1,000 screenings to begin to approach the annual limit". [ 38 ] [ 39 ] [ 40 ]


John Sedat, the principal author of the UCSF letter, responded in November 2010 that the White House's claim that full-body scanners pose no health risks to air travelers is in error, adding that the White House statement has "many misconceptions, and we will write a careful answer pointing out their errors". [ 41 ]


In a December 2, 2010 letter to the House of Representatives, Dr. Steven Smith, inventor of the body scanner in 1991, stated that the concerns of Brenner and UCSF regarding the skin dose of backscatter scanners is incorrect and the result of a confusion between dose and imaging penetration. Smith demonstrated this difference with two experiments using plastic (with a similar  rate of absorption  as body tissue), copper (the image subject), and an x-ray scanner. The dose-penetration experiment shows that 5 and 50 mm (0.20 and 1.97 in) plastic samples absorb 5% and 50% of the beam intensity respectively, whereas the imaging penetration experiment shows that 4.8 and 10 mm (0.19 and 0.39 in) plastic samples reduce the image darkness by 23% and 50% respectively. Dr. Smith states that those who calculate high skin dosage have incorrectly used the shallow imaging penetration value of a few millimeters (c. 0.16 in), whereas the actual dosage is calculated by the deeper dose penetration. [ 42 ]


The TSA has also made public various independent safety assessments of the Secure 1000 Backscatter X-ray Scanner. [ 43 ] [ 44 ] [ 45 ] [ 46 ]


Radiation safety authorities including the  National Council on Radiation Protection and Measurements , The Health Physics Society and the  American College of Radiology , have stated that there is no specific evidence that full-body scans are unsafe. [ 47 ]  The Secure 1000 Backscatter X-ray scanner was developed in 1992 by Dr. Steve Smith. [ 9 ]  The scanner has been studied extensively for almost 20 years by the leading independent radiation safety authorities in the United States. [ 47 ] [ 48 ]  Experimental and epidemiological data do not support the proposition, however, that there is a threshold dose of radiation below which there is no increased risk of cancer. [ 49 ]


The UK Health Protection Agency has completed an analysis of the X-ray dose from backscatter scanners and has written that the dose is extremely low and "about the same as people receive from  background radiation  in an hour". [ 50 ]


The  Health Physics Society  (HPS) reports that a person undergoing a backscatter scan receives approximately 0.05  μSv  (0.005  mrem ) of radiation; American Science and Engineering Inc. reports 0.09 μSv (0.009 mrem). At the high altitudes typical of commercial flights, naturally occurring cosmic radiation is considerably higher than at ground level.  The radiation dose for a six-hour flight is 20 μSv (2 mrem) – 200 to 400 times larger than a backscatter scan.  The  Nuclear Regulatory Commission  limits radiation exposure to the public to less than 1 mSv (100 mrem) per year from  nuclear power plants . [ 51 ]  While this is not specifically for airline-associated radiation, the limit is an effective proxy for understanding what level is deemed safe by a regulatory agency.


According to a draft [ needs update ]  standard on the United States FDA website, the allowable dose from a scan would be 0.1 μSv, and that report uses a model whereby a 0.01 μSv dose increases an individual's risk of death by cancer during his or her lifetime by  5 × 10 −10 . [ 52 ]  Since the dose limit is ten times higher than 0.01 μSv, their model would predict one additional cancer death per 200 million scans. Since the airports in the UK handled 218 million passengers in 2009, [ 53 ]  if all passengers in the UK were scanned at the maximum dosage, then each year this would produce on average one additional cancer death (since there would be 200 million scans per year that the scanners were in operation), though usually each death would not occur in the same year as the particular scan that caused it, since the cancer may take years to grow. In addition, additional people would be given cancer but would die from other causes.


There may not yet be evidence of hereditary effects of x-rays administered by backscatter scanners, but backscatter scanners use the same kind of x-ray photons as are produced in medical x-ray machines but expose the subject at a considerably lower dose, so it is possible that the results from medical radiology may be relevant, at least until a study is done of any effects specific to backscatter x-ray machines. Fathers exposed to medical diagnostic x-rays are more likely to have infants who contract leukemia, especially if exposure is closer to conception or includes two or more X-rays of the lower gastrointestinal (GI) tract or lower abdomen. [ 54 ]  In medical radiography the x-ray beam is adjusted to expose only the area of which an image is required, so that generally shielding is applied to the patient to avoid exposing the gonads, [ 55 ]  whereas in an airport backscatter scan, the testicles of men and boys will be deliberately subjected to the direct beam in order to check for weapons in the underpants, and some radiation will also reach the ovaries of female subjects. A linear dose-response relationship has been observed between x-ray dose and double-strand breaks in DNA in human sperm. [ 56 ]


Extrapolations of cancer risk from minuscule exposures to radiation across large populations, however, are not supported by analysis by the  National Council on Radiation Protection  (NCRP). On May 26, 2010, NCRP issued a press release to address such comments about full body scanners that are compliant with ANSI N43.17. In Commentary No. 16 issued on May 26, 2010, it reads as follows:


As stated in NCRP Report No. 121 (1995), Principles and Application of Collective Dose in Radiation Protection, the summation of trivial average risks over very large populations or time periods into a single value produces a distorted image of risk, completely out of perspective with risks accepted every day, both voluntarily and involuntarily. [ 57 ]


According to NCRP, the use of statistical extrapolations that predict 1 death for every 200 million persons scanned for example (as above) is an unrealistic over-estimation. [ 57 ] [ 58 ]


Other scientists at  Columbia University  have made the following statements in support of the safety of body scanners: [ 59 ]


"A passenger would need to be scanned using a backscatter scanner, from both the front and the back, about 200,000 times to receive the amount of radiation equal to one typical CT scan," said Dr. Andrew J. Einstein, director of cardiac CT research at Columbia University Medical Center in New York City.


"Another way to look at this is that if you were scanned with a backscatter scanner every day of your life, you would still only receive a tenth of the dose of a typical CT scan," he said.


By comparison, the amount of radiation from a backscatter scanner is equivalent to about 10 minutes of natural background radiation in the United States, Einstein said. "I believe that the general public has nothing to worry about in terms of the radiation from airline scanning," he added.


For moms-to-be, no evidence supports an increased risk of miscarriage or fetal abnormalities from these scanners, Einstein added.


"A pregnant woman will receive much more radiation from cosmic rays she is exposed to while flying than from passing through a scanner in the airport," he said.


Furthermore, other scientists claim the health effects of backscatter are well understood whereas those from  millimeter wave scanners  are not:


"From a radiation standpoint there has been no evidence that there is really any untoward effect from the use of this device [backscatter scanner], so I would not be concerned about it from a radiation dose standpoint – the issues of personal privacy are a different thing," he said.


The health effects of the more common  millimeter wave scanner  are largely unknown, and at least one expert believes a safety study is warranted.


"I am very interested in performing a National Council on Radiation Protection and Measurements study on the use of millimeter-wave security screening systems," said Thomas S. Tenforde, council president.


However, no long-term studies have been done on the health effects of millimeter wave scanners. [ 59 ]


Experts evaluating backscatter x-ray machine technology have also argued that defects in the machines, damage from normal wear-and-tear, or software errors could focus an intense dose of radiation on just one spot of the body. [ 33 ]  For example, Dr. Peter Rez, a professor of physics at Arizona State University, has said, "The thing that worries me the most, is not what happens if the machine works as advertised, but what happens if it doesn't", adding that a potential malfunction of the machine could increase the radiation dose. [ 60 ] [ 61 ]


The designers and manufacturers of backscatter X-ray scanners claim that the scanners are designed to prevent the occurrence of these kinds of errors. The scanners' safety requirements include fail-safe controls and multiple overlapping interlocks. These features, combined with fault analysis, ensure that failure of any subsystem results in non-operation of the x-ray generator to prevent accidental exposures. In the United States, the TSA requires that certification to the ANSI N43.17 safety standard is performed by a third party and not by the manufacturer themselves. [ 62 ]


The  European Commission  issued a report stating that backscatter x-ray scanners pose no known health risk, and that "assuming all other conditions equal", that backscatter x-ray scanners, which expose people to ionizing radiation, should not be used when millimeter-wave scanners that "have less effects on the human body" are available. [ 63 ]


However, the European Commission report provides no data substantiating its claim that "all other conditions are equal". One area where backscatter X-ray scanners can provide better performance than MM wave scanners, for example, is in the inspection of the shoes, groin and armpit regions of the body. [ 64 ]


In a study published in the  Archives of Internal Medicine  on March 28, 2011, researchers at the University of California "calculated that fully implementing backscatter scanners would not significantly increase the lifetime risk of cancer for travelers". [ 65 ] [ 66 ]  The researchers calculated that for every 100 million passengers who flew seven one-way flights, there would be one additional cancer. [ 67 ] [ 68 ]


In March 2012, scientist and blogger Jonathan Corbett demonstrated the ineffectiveness of the technology by publishing a viral video showing how he was able to get a metal box through backscatter x-ray and millimeter wave scanners (including the currently-used "Automated Target Recognition" scanners) in two US airports. [ 69 ] [ 70 ]  In April 2012, Corbett released a second video interviewing a TSA screener, who described firearms and simulated explosives passing through the scanners during internal testing and training. [ 71 ]


Backscatter scanners installed by the TSA until 2013 were unable to screen adequately for security threats inside hats and head coverings, casts, prosthetics and loose clothing. [ 72 ] [ 73 ]   This technology limitation of current scanners often requires these persons to undergo additional screening by hand or other methods and can cause additional delay or feelings of harassment. [ 74 ]


The next generation of backscatter scanners are able to screen these types of clothing, according to manufacturers; however, these machines are not currently in use in public airports. [ 75 ]


In Germany, field tests on more than 800,000 passengers over a 10-month trial period concluded that scanners were effective, but not ready to be deployed in German airports due to a high rate of false alarms. [ 76 ]  The Italian Civil Aviation Authority removed scanners from airports after conducting a study that revealed them to be inaccurate and inconvenient. [ 77 ]  The European Commission decided to effectively ban backscatter machines. [ 78 ]  In a 2011 staff report by Republican Members of Congress about the TSA, airport body scanners were described as "ineffective" and "easily thwarted". [ 79 ]


In the US, manufacturers of security related equipment can apply for protection under the SAFETY act, which limits their financial liability in product liability cases to the amount of their insurance coverage.  The Rapiscan Secure 1000 was listed in 2006. [ 80 ]


In the US, an X-ray system can be considered to comply with requirements for general purpose security screening of humans if the device complies with American National Standards Institute (ANSI) Standard #N43.17. [ 81 ] [ 82 ]


In the most general sense, N43.17 states that a device can be used for general purpose security screening of humans if the dose to the subject is less than 0.25 μSv (25 μrem) per examination and complies with other requirements of the standard.  This is comparable to the average dose due to background radiation (i.e. radioactivity within the surrounding environment) at sea level in 1.5 hours; it is also comparable to the dose from  cosmic rays  when traveling in an airplane at cruising altitude for two minutes. [ 83 ]


Many types of X-ray systems can be designed to comply with ANSI N43.17 including transmission X-ray, [ 84 ]  backscatter X-ray and gamma ray systems. Not all backscatter X-ray devices necessarily comply with ANSI N43.17; only the manufacturer or end user can confirm compliance of a particular product to the standard.


ANSI standards use a standard of measurement algorithm called "effective dose" that considers the different exposure of all parts of the body and then weights them differently. The interior of the human body is given more weight in this survey, and the exterior, including the skin organ, are given less weight.


Some people wish to prevent either the loss of privacy or the possibility of health problems or genetic damage that might be associated with being subjected to a backscatter X-ray scan.  One company sells X-ray absorbing underwear which is said to have X-ray absorption equivalent to 0.5 mm (0.020 in) of lead. [ 85 ]   Another product, Flying Pasties, "are designed to obscure the most private parts of the human body when entering full body airport scanners", but their description does not seem to claim any protection from the X-ray beam penetrating the body of the person being scanned. [ 86 ]