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110-471: The Therac-25 was involved in at least six accidents between 1985 and 1987, in which some patients were given massive overdoses of radiation . Because of concurrent programming errors (also known as race conditions), it sometimes gave its patients radiation doses that were hundreds of times greater than normal, resulting in death or serious injury. These accidents highlighted the dangers of software control of safety-critical systems. The Therac-25 has become

220-517: A radioactive tracer isotope is the source of the positrons used in positron emission tomography (PET scan). Henri Becquerel , while experimenting with fluorescence , accidentally found out that uranium exposed a photographic plate, wrapped with black paper, with some unknown radiation that could not be turned off like X-rays . Ernest Rutherford continued these experiments and discovered two different kinds of radiation: He published his results in 1899. In 1900, Becquerel measured

330-448: A "tremendous force of heat...this red-hot sensation." The technician entered the room, to whom Katie stated, "you burned me." The technician assured her this was not possible. She returned home where, in the following days, she experienced reddening of the treatment area. Shortly after, her shoulder became locked in place and she experienced spasms. Within two weeks, the aforementioned redness spread from her chest to her back, indicating that

440-399: A high neutron activation cross section to shield neutrons will result in the shielding material itself becoming radioactive and hence more dangerous than if it were not present. There are many types of shielding strategies that can be used to reduce the effects of radiation exposure. Internal contamination protective equipment such as respirators are used to prevent internal deposition as

550-539: A higher dose than would otherwise be expected. The dose to the targeted tissue mass must be averaged over the entire body mass, most of which receives negligible radiation, to arrive at a whole-body absorbed dose that can be compared to the table above. Exposure to high doses of radiation causes DNA damage, later creating serious and even lethal chromosomal aberrations if left unrepaired. Ionizing radiation can produce reactive oxygen species , and does directly damage cells by causing localized ionization events. The former

660-434: A latent period averaging 20 to 40 years. Acute effects of ionizing radiation were first observed when Wilhelm Röntgen intentionally subjected his fingers to X-rays in 1895. He published his observations concerning the burns that developed that eventually healed, and misattributed them to ozone. Röntgen believed the free radical produced in air by X-rays from the ozone was the cause, but other free radicals produced within

770-431: A latent phase may occur and last from a few days up to several weeks, when intense reddening, blistering , and ulceration of the irradiated site is visible. In most cases, healing occurs by regenerative means; however, very large skin doses can cause permanent hair loss, damaged sebaceous and sweat glands , atrophy , fibrosis (mostly keloids ), decreased or increased skin pigmentation, and ulceration or necrosis of

880-437: A lesson to be drawn from the incident is to not assume that reused software is safe: "A naive assumption is often made that reusing software or using commercial off-the-shelf software will increase safety because the software will have been exercised extensively. Reusing software modules does not guarantee safety in the new system to which they are transferred ..." In response to incidents like those associated with Therac-25,

990-453: A major part in radiotherapy accidents. The latter of the two is caused by the failure of equipment software used to monitor the radiational dose given. Human error has played a large part in accidental exposure incidents, including some of the criticality accidents, and larger scale events such as the Chernobyl disaster . Other events have to do with orphan sources , in which radioactive material

1100-535: A neutron is converted into a proton , an electron, and an electron antineutrino (the antiparticle of the neutrino ): This process is mediated by the weak interaction . The neutron turns into a proton through the emission of a virtual W boson . At the quark level, W emission turns a down quark into an up quark, turning a neutron (one up quark and two down quarks) into a proton (two up quarks and one down quark). The virtual W boson then decays into an electron and an antineutrino. β− decay commonly occurs among

1210-489: A new double pass concept for electron acceleration in a more confined space, changing its energy source from klystron to magnetron . In certain techniques, the electrons produced are used directly, while in others they are made to collide against a tungsten anode to produce X-ray beams. This dual accelerator concept was applied to the Therac-20 and Therac-25, with the latter being much more compact, versatile, and easy to use. It

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1320-399: A patient presented for his ninth treatment session for a tumor on his back. The treatment was set to be 22-MeV of electrons with a dose of 180 rad in an area of 10x17 cm, with an accumulated radiation in 6 weeks of 6000 rad. The experienced operator entered the session data and realized that she had written an “x” for ‘x-ray’ instead of an “e” for ‘electron beam’ as the type of treatment. With

1430-467: A reduction in dose rate below 0.1 Gy/h also tends to reduce cell death. This technique is routinely used in radiotherapy. The human body contains many types of cells and a human can be killed by the loss of a single type of cells in a vital organ. For many short term radiation deaths (3–30 days), the loss of two important types of cells that are constantly being regenerated causes death. The loss of cells forming blood cells ( bone marrow ) and

1540-486: A result of inhalation and ingestion of radioactive material. Dermal protective equipment, which protects against external contamination, provides shielding to prevent radioactive material from being deposited on external structures. While these protective measures do provide a barrier from radioactive material deposition, they do not shield from externally penetrating gamma radiation. This leaves anyone exposed to penetrating gamma rays at high risk of ARS. Naturally, shielding

1650-448: A short period of time (> ~0.1 Gy/h). Alpha and beta radiation have low penetrating power and are unlikely to affect vital internal organs from outside the body. Any type of ionizing radiation can cause burns, but alpha and beta radiation can only do so if radioactive contamination or nuclear fallout is deposited on the individual's skin or clothing. Gamma and neutron radiation can travel much greater distances and penetrate

1760-432: A short period of time. Symptoms can start within an hour of exposure, and can last for several months. Early symptoms are usually nausea, vomiting and loss of appetite. In the following hours or weeks, initial symptoms may appear to improve, before the development of additional symptoms, after which either recovery or death follow. ARS involves a total dose of greater than 0.7 Gy (70 rad ), that generally occurs from

1870-655: A source outside the body, delivered within a few minutes. Sources of such radiation can occur accidentally or intentionally. They may involve nuclear reactors , cyclotrons , certain devices used in cancer therapy , nuclear weapons , or radiological weapons . It is generally divided into three types: bone marrow, gastrointestinal, and neurovascular syndrome, with bone marrow syndrome occurring at 0.7 to 10 Gy, and neurovascular syndrome occurring at doses that exceed 50 Gy. The cells that are most affected are generally those that are rapidly dividing. At high doses, this causes DNA damage that may be irreparable. Diagnosis

1980-531: A standard case study in health informatics , software engineering , and computer ethics . It highlights the dangers of engineer overconfidence after the engineers dismissed end-user reports, leading to severe consequences. The French company CGR manufactured the Neptune and Sagittaire linear accelerators. In the early 1970s, CGR and the Canadian public company Atomic Energy of Canada Limited (AECL) collaborated on

2090-572: A third- or fourth-generation cephalosporin with pseudomonal coverage: e.g., cefepime , ceftazidime , or an aminoglycoside: i.e. gentamicin , amikacin ). The prognosis for ARS is dependent on the exposure dose, with anything above 8 Gy being almost always lethal, even with medical care. Radiation burns from lower-level exposures usually manifest after 2 months, while reactions from the burns occur months to years after radiation treatment. Complications from ARS include an increased risk of developing radiation-induced cancer later in life. According to

2200-409: A type of ionizing radiation , and for radiation protection purposes, they are regarded as being more ionising than gamma rays , but less ionising than alpha particles . The higher the ionising effect, the greater the damage to living tissue, but also the lower the penetrating power of the radiation through matter. An unstable atomic nucleus with an excess of neutrons may undergo β decay, where

2310-447: Is a high-energy, high-speed electron or positron emitted by the radioactive decay of an atomic nucleus , known as beta decay . There are two forms of beta decay, β decay and β decay, which produce electrons and positrons, respectively. Beta particles with an energy of 0.5 MeV have a range of about one metre in the air; the distance is dependent on the particle's energy and the air's density and composition. Beta particles are

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2420-439: Is absorbed while passing through the product. If the product is made too thick or thin, a correspondingly different amount of radiation will be absorbed. A computer program monitoring the quality of the manufactured paper will then move the rollers to change the thickness of the final product. An illumination device called a betalight contains tritium and a phosphor . As tritium decays , it emits beta particles; these strike

2530-431: Is based on a history of exposure and symptoms. Repeated complete blood counts (CBCs) can indicate the severity of exposure. Treatment of ARS is generally supportive care . This may include blood transfusions , antibiotics , colony-stimulating factors , or stem cell transplant . Radioactive material remaining on the skin or in the stomach should be removed. If radioiodine was inhaled or ingested, potassium iodide

2640-659: Is difficult because of confounding factors. ARS may be accompanied by conventional injuries such as steam burns, or may occur in someone with a pre-existing condition undergoing radiotherapy. There may be multiple causes for death, and the contribution from radiation may be unclear. Some documents may incorrectly refer to radiation-induced cancers as radiation poisoning, or may count all overexposed individuals as survivors without mentioning if they had any symptoms of ARS. The following table includes only those known for their attempted survival with ARS. These cases exclude chronic radiation syndrome such as Albert Stevens , in which radiation

2750-443: Is divided into three main presentations: hematopoietic , gastrointestinal , and neuro vascular . These syndromes may be preceded by a prodrome . The speed of symptom onset is related to radiation exposure, with greater doses resulting in a shorter delay in symptom onset. These presentations presume whole-body exposure, and many of them are markers that are invalid if the entire body has not been exposed. Each syndrome requires that

2860-558: Is during the 1999 Tokaimura nuclear accident , where technician Hisashi Ouchi had lost a majority of his skin due to the high amounts of radiation he absorbed during the irradiation. This effect had been demonstrated previously with pig skin using high energy beta sources at the Churchill Hospital Research Institute, in Oxford . ARS is caused by exposure to a large dose of ionizing radiation (> ~0.1 Gy) over

2970-683: Is especially harmful. While DNA damage happens frequently and naturally in the cell from endogenous sources, clustered damage is a unique effect of radiation exposure. Clustered damage takes longer to repair than isolated breakages, and is less likely to be repaired at all. Larger radiation doses are more prone to cause tighter clustering of damage, and closely localized damage is increasingly less likely to be repaired. Somatic mutations cannot be passed down from parent to offspring, but these mutations can propagate in cell lines within an organism. Radiation damage can also cause chromosome and chromatid aberrations, and their effects depend on in which stage of

3080-469: Is exposed to a given subject over a long duration. The table also necessarily excludes cases where the individual was exposed to so much radiation that death occurred before medical assistance or dose estimations could be made, such as an attempted cobalt-60 thief who reportedly died 30 minutes after exposure. The result column represents the time of exposure to the time of death attributed to the short and long term effects attributed to initial exposure. As ARS

3190-436: Is measured by a whole-body absorbed dose , the exposure column only includes units of gray (Gy). Thousands of scientific experiments have been performed to study ARS in animals. There is a simple guide for predicting survival and death in mammals, including humans, following the acute effects of inhaling radioactive particles. Beta radiation A beta particle , also called beta ray or beta radiation (symbol β ),

3300-456: Is more strongly ionizing than gamma radiation. When passing through matter, a beta particle is decelerated by electromagnetic interactions and may give off bremsstrahlung X-rays . In water, beta radiation from many nuclear fission products typically exceeds the speed of light in that material (which is about 75% that of light in vacuum), and thus generates blue Cherenkov radiation when it passes through water. The intense beta radiation from

3410-467: Is not hazardous once fallout is no longer being deposited. For example, assume the shelter is in an area of heavy fallout and the dose rate outside is 400  roentgen (R) per hour, enough to give a potentially fatal dose in about an hour to a person exposed in the open. If a person needs to be exposed for only 10 seconds to dump a bucket, in this 1/360 of an hour he will receive a dose of only about 1 R. Under war conditions, an additional 1-R dose

Therac-25 - Misplaced Pages Continue

3520-399: Is of little concern." In peacetime, radiation workers are taught to work as quickly as possible when performing a task that exposes them to radiation. For instance, the recovery of a radioactive source should be done as quickly as possible. Usually, matter attenuates radiation, so placing any mass (e.g., lead, dirt, sandbags, vehicles, water, even air) between humans and the source will reduce

3630-428: Is only necessary to protect enough bone marrow to repopulate the exposed areas of the body with the shielded supply. This concept allows for the development of lightweight mobile radiation protection equipment, which provides adequate protection, deferring the onset of ARS to much higher exposure doses. One example of such equipment is the 360 gamma , a radiation protection belt that applies selective shielding to protect

3740-452: Is placed on a fixed stretcher. Above them is a turntable to which the components that modify the electron beam are fixed. The turntable has a position for the X-ray mode (photons), another position for the electron mode and a third position for making adjustments using visible light. In this position an electron beam is not expected, and a light that is reflected in a stainless steel mirror simulates

3850-510: Is rarer, with an event possibly occurring during the solar storm of 1859 . Intentional exposure is controversial as it involves the use of nuclear weapons , human experiments , or is given to a victim in an act of murder. The intentional atomic bombings of Hiroshima and Nagasaki resulted in tens of thousands of casualties; the survivors of these bombings are known today as hibakusha . Nuclear weapons emit large amounts of thermal radiation as visible, infrared, and ultraviolet light, to which

3960-506: Is recommended. Complications such as leukemia and other cancers among those who survive are managed as usual. Short-term outcomes depend on the dose exposure. ARS is generally rare. A single event can affect a large number of people, as happened in the atomic bombings of Hiroshima and Nagasaki and the Chernobyl nuclear power plant disaster . ARS differs from chronic radiation syndrome , which occurs following prolonged exposures to relatively low doses of radiation. Classically, ARS

4070-501: Is the whole-body absorbed dose . Several related quantities, such as the equivalent dose , effective dose , and committed dose , are used to gauge long-term stochastic biological effects such as cancer incidence, but they are not designed to evaluate ARS. To help avoid confusion between these quantities, absorbed dose is measured in units of grays (in SI , unit symbol Gy ) or rad (in CGS ), while

4180-464: Is typically made based on a history of significant radiation exposure and suitable clinical findings. An absolute lymphocyte count can give a rough estimate of radiation exposure. Time from exposure to vomiting can also give estimates of exposure levels if they are less than 10 Gy (1000 rad). A guiding principle of radiation safety is as low as reasonably achievable (ALARA). This means try to avoid exposure as much as possible and includes

4290-431: Is unknowingly kept, sold, or stolen. The Goiânia accident is an example, where a forgotten radioactive source was taken from a hospital, resulting in the deaths of 4 people from ARS. Theft and attempted theft of radioactive material by clueless thieves has also led to lethal exposure in at least one incident. Exposure may also come from routine spaceflight and solar flares that result in radiation effects on earth in

4400-409: Is very damaging to DNA, while the latter events create clusters of DNA damage. This damage includes loss of nucleobases and breakage of the sugar-phosphate backbone that binds to the nucleobases. The DNA organization at the level of histones , nucleosomes , and chromatin also affects its susceptibility to radiation damage . Clustered damage, defined as at least two lesions within a helical turn,

4510-464: The IEC 62304 standard was created, which introduces development life cycle standards for medical device software and specific guidance on using software of unknown pedigree . Radiation poisoning Acute radiation syndrome ( ARS ), also known as radiation sickness or radiation poisoning , is a collection of health effects that are caused by being exposed to high amounts of ionizing radiation in

Therac-25 - Misplaced Pages Continue

4620-496: The "Malfunction 54" message was a "dose input 2" error. A technician later testified that "dose input 2" meant that the radiation delivered was either too high or too low. The radiation monitor (dosimeter) marked 6 units supplied when it had demanded 202 units. The operator pressed P ( Proceed : continue). The machine stopped again with the message "Malfunction 54" (error 54) and the dosimeter indicated that it had delivered fewer units than required. The surveillance camera in

4730-500: The 1958 Cecil Kelley criticality accident , where the absorbed doses in Gy or rad are the only useful quantities, because of the targeted nature of the exposure to the body. Radiotherapy treatments are typically prescribed in terms of the local absorbed dose, which might be 60 Gy or higher. The dose is fractionated to about 2 Gy per day for curative treatment, which allows normal tissues to undergo repair , allowing them to tolerate

4840-522: The Therac-25 was built in 1976 and was put on the market in late 1982. The software for the Therac-25 was developed by one person over several years using PDP-11 assembly language. It was an evolution of the Therac-6 software. In 1986, the programmer left AECL. In a subsequent lawsuit, lawyers were unable to identify the programmer or learn about his qualification and experience. Five machines were installed in

4950-591: The United States and six in Canada. After the accidents, in 1988 AECL dissolved the AECL Medical section and the company Theratronics International Ltd took over the maintenance of the installed Therac-25 machines. The machine had three modes of operation, with a turntable moving some apparatus into position for each of those modes: either a light, some scan magnets , or a tungsten target and flattener . The patient

5060-407: The absolute value of the binding energy of the daughter nucleus is greater than that of the parent nucleus, i.e., the daughter nucleus is a lower-energy state. The accompanying decay scheme diagram shows the beta decay of caesium-137 . Cs is noted for a characteristic gamma peak at 661 keV, but this is actually emitted by the daughter radionuclide Ba. The diagram shows the type and energy of

5170-414: The area and was hospitalized on July 30. She was suspected of a radiation overdose and the machine was taken out of service. On November 3, 1985, the patient died of cancer, although the autopsy mentioned that if she had not died then, she would have had to undergo a hip replacement due to damage from the radiation overdose. A technician estimated that she received between 13,000 and 17,000 rad. The incident

5280-412: The atmosphere is largely transparent. This event is also known as "flash", where radiant heat and light are bombarded into any given victim's exposed skin, causing radiation burns. Death is highly likely, and radiation poisoning is almost certain if one is caught in the open with no terrain or building masking-effects within a radius of 0–3 km from a 1 megaton airburst. The 50% chance of death from

5390-411: The beam. In this position there is no ion chamber acting as a radiation dosimeter because the radiation beam is not expected to function. The turntable has some microswitches that indicate the position to the computer. When the plate is in one of the three allowed fixed positions a plunger locks it by interlocking . In this type of machine, electromechanical locks were traditionally used to ensure that

5500-471: The beams. After 5 seconds the machine stopped and displayed a message that quickly disappeared. Since the machine was paused, the operator pressed P (Proceed : continue). The machine stopped, showing "Flatness" as the reason. The operator heard the patient on the intercom, but could not understand him, and entered the room. The patient had felt a severe burning sensation in his chest. The screen showed that he had only been given 7 rad. A few hours later,

5610-548: The blast extends out to ~8 km from a 1 megaton atmospheric explosion. Scientific testing on humans within the United States occurred extensively throughout the atomic age. Experiments took place on a range of subjects including, but not limited to; the disabled, children, soldiers, and incarcerated persons, with the level of understanding and consent given by subjects varying from complete to none. Since 1997 there have been requirements for patients to give informed consent, and to be notified if experiments were classified. Across

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5720-560: The body are now understood to be more important. David Walsh first established the symptoms of radiation sickness in 1897. Ingestion of radioactive materials caused many radiation-induced cancers in the 1930s, but no one was exposed to high enough doses at high enough rates to bring on ARS. The atomic bombings of Hiroshima and Nagasaki resulted in high acute doses of radiation to a large number of Japanese people, allowing for greater insight into its symptoms and dangers. Red Cross Hospital Surgeon Terufumi Sasaki led intensive research into

5830-599: The body easily, so whole-body irradiation generally causes ARS before skin effects are evident. Local gamma irradiation can cause skin effects without any sickness. In the early twentieth century, radiographers would commonly calibrate their machines by irradiating their own hands and measuring the time to onset of erythema . Accidental exposure may be the result of a criticality or radiotherapy accident. There have been numerous criticality accidents dating back to atomic testing during World War II, while computer-controlled radiation therapy machines such as Therac-25 played

5940-502: The bone marrow stored in the pelvic area as well as other radio sensitive organs in the abdominal region without hindering functional mobility. Where radioactive contamination is present, an elastomeric respirator , dust mask , or good hygiene practices may offer protection, depending on the nature of the contaminant. Potassium iodide (KI) tablets can reduce the risk of cancer in some situations due to slower uptake of ambient radioiodine. Although this does not protect any organ other than

6050-448: The cells in the digestive system ( microvilli , which form part of the wall of the intestines ) is fatal. Treatment usually involves supportive care with possible symptomatic measures employed. The former involves the possible use of antibiotics , blood products , colony stimulating factors , and stem cell transplant . There is a direct relationship between the degree of the neutropenia that emerges after exposure to radiation and

6160-467: The construction of linear accelerators controlled by a DEC PDP-11 minicomputer: the Therac-6, which produced X-rays of up to 6 MeV, and the Therac-20, which could produce X-rays or electrons of up to 20 MeV. The computer increased ease of use because the accelerator could operate without it. CGR developed the software for the Therac-6 and reused some subroutines for the Therac-20. In 1981, the two companies ended their collaboration agreement. AECL developed

6270-403: The controversial but commonly applied linear no-threshold model , any exposure to ionizing radiation, even at doses too low to produce any symptoms of radiation sickness, can induce cancer due to cellular and genetic damage. The probability of developing cancer is a linear function with respect to the effective radiation dose . Radiation cancer may occur after ionizing radiation exposure following

6380-416: The cursor she went up and changed the “x” to an “e” and since the rest of the parameters were correct she pressed ↵ Enter until she got down to the command box. All parameters were marked "Verified" and the message "Rays ready" was displayed. She hit the B key ("Beam on"). The machine stopped and displayed the message "Malfunction 54" (error 54). It also showed 'Treatment pause'. The manual said that

6490-422: The day. The technicians were unaware that the patient had received a massive dose of radiation between 16,500 and 25,000 rads in less than a second over an area of one cm. The crackling of the machine had been produced by saturation of the ionization chambers, which had the consequence that they indicated that the applied radiation dose had been very low. Over the following weeks the patient experienced paralysis of

6600-526: The effects on humans subjected to the atomic bombings of Hiroshima and Nagasaki , the indigenous peoples of the Marshall Islands subjected to the Castle Bravo thermonuclear bomb, animal studies and lab experiment accidents, have been compiled by the U.S. Department of Defense . A person who was less than 1 mile (1.6 km) from the atomic bomb Little Boy 's hypocenter at Hiroshima, Japan,

6710-416: The electron beam to be set for X-ray mode without the X-ray target being in place. A second fault allowed the electron beam to activate during field-light mode, during which no beam scanner was active or target was in place. Previous models had hardware interlocks to prevent such faults, but the Therac-25 had removed them, depending instead on software checks for safety. The high-current electron beam struck

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6820-403: The electron's path under a magnetic field. Beta particles can be used to treat health conditions such as eye and bone cancer and are also used as tracers. Strontium-90 is the material most commonly used to produce beta particles. Beta particles are also used in quality control to test the thickness of an item, such as paper , coming through a system of rollers. Some of the beta radiation

6930-417: The emitted radiation, its relative abundance, and the daughter nuclides after decay. Phosphorus-32 is a beta emitter widely used in medicine. It has a short half-life of 14.29 days and decays into sulfur-32 by beta decay as shown in this nuclear equation: 1.709  MeV of energy is released during the decay. The kinetic energy of the electron varies with an average of approximately 0.5 MeV and

7040-406: The entire body from high energy gamma radiation is optimal, but the required mass to provide adequate attenuation makes functional movement nearly impossible. In the event of a radiation catastrophe, medical and security personnel need mobile protection equipment in order to safely assist in containment, evacuation, and many other necessary public safety objectives. Research has been done exploring

7150-415: The error and they only got it after following the instructions of the physicist so that the data entry was very rapid. On January 17, 1987, a patient was to receive a treatment with two film-verification exposures of 4 and 3 rads, plus a 79-rad photon treatment for a total exposure of 86 rads. Film was placed under the patient and 4 rads were administered through a 22 cm × 18 cm opening. The machine

7260-463: The error message "H-tilt", the treatment pause indication and the dosimeter indicating that no radiation had been applied. The operator pressed the P key (Proceed : continue). The machine stopped again. The operator repeated the process five times until the machine stopped the treatment. A technician was called and found no problem. The machine was used to treat six other patients on the same day. The patient complained of burning and swelling in

7370-448: The excitation of scintillators is used in scintillation counters . The following table shows radiation quantities in SI and non-SI units: The energy contained within individual beta particles is measured via beta spectrometry ; the study of the obtained distribution of energies as a spectrum is beta spectroscopy . Determination of this energy is done by measuring the amount of deflection of

7480-403: The exposed tissue. As seen at Chernobyl , when skin is irradiated with high energy beta particles , moist desquamation (peeling of skin) and similar early effects can heal, only to be followed by the collapse of the dermal vascular system after two months, resulting in the loss of the full thickness of the exposed skin. Another example of skin loss caused by high-level exposure of radiation

7590-429: The feasibility of partial body shielding, a radiation protection strategy that provides adequate attenuation to only the most radio-sensitive organs and tissues inside the body. Irreversible stem cell damage in the bone marrow is the first life-threatening effect of intense radiation exposure and therefore one of the most important bodily elements to protect. Due to the regenerative property of hematopoietic stem cells , it

7700-438: The form of solar storms . During spaceflight, astronauts are exposed to both galactic cosmic radiation (GCR) and solar particle event (SPE) radiation. The exposure particularly occurs during flights beyond low Earth orbit (LEO). Evidence indicates past SPE radiation levels that would have been lethal for unprotected astronauts. GCR levels that might lead to acute radiation poisoning are less well understood. The latter cause

7810-414: The fuel rods of swimming pool reactors can thus be visualized through the transparent water that covers and shields the reactor (see illustration at right). The ionizing or excitation effects of beta particles on matter are the fundamental processes by which radiometric detection instruments detect and measure beta radiation. The ionization of gas is used in ion chambers and Geiger–Müller counters , and

7920-531: The hospital and the manufacturer of the machine. In November 1985, the AECL was notified of the lawsuit. It was not until March 1986, after another incident involving the Therac-25, that the AECL informed the FDA that it had received a complaint from the patient. Due to the radiation overdose, her breast had to be surgically removed, an arm and shoulder were immobilized, and she was in constant pain. The treatment printout function

8030-422: The increased risk of developing infection. Since there are no controlled studies of therapeutic intervention in humans, most of the current recommendations are based on animal research. The treatment of established or suspected infection following exposure to radiation (characterized by neutropenia and fever) is similar to the one used for other febrile neutropenic patients. However, important differences between

8140-570: The injured patients later died as a result of the overdose. A Therac-25 had been in operation for six months in Marietta, Georgia at the Kennestone Regional Oncology Center when, on June 3, 1985, applied radiation therapy treatment following a lumpectomy was being performed on 61-year-old woman Katie Yarbrough. She was set to receive a 10-MeV dose of electron therapy to her clavicle . When therapy began, she stated she experienced

8250-460: The isolates causing sepsis. Because aerobic and facultative Gram-positive bacteria (mostly alpha-hemolytic streptococci ) cause sepsis in about a quarter of the victims, coverage for these organisms may also be needed. A standardized management plan for people with neutropenia and fever should be devised. Empirical regimens contain antibiotics broadly active against Gram-negative aerobic bacteria ( quinolones : i.e., ciprofloxacin , levofloxacin ,

8360-411: The left arm, nausea, vomiting, and ended up being hospitalized for radiation-induced myelitis of the spinal cord. His legs, mid-diaphragm and vocal cords ended up paralyzed. He also had recurrent herpes simplex skin infections. He died five months after the overdose. From the day after the accident, AECL technicians checked the machine and were unable to replicate error 54. They checked the grounding of

8470-455: The machine to rule out electric shock as the cause. The machine was back in operation on April 7, 1986. On April 11, 1986, a patient was to receive electron treatment for skin cancer on the face. The prescription was 10 MeV for an area of 7x10 cm. The operator was the same as the one in the March incident, three weeks earlier. After filling in all the treatment data she realized that she had to change

8580-660: The medium ionising power. Although the beta particles given off by different radioactive materials vary in energy, most beta particles can be stopped by a few millimeters of aluminium . However, this does not mean that beta-emitting isotopes can be completely shielded by such thin shields: as they decelerate in matter, beta electrons emit secondary gamma rays, which are more penetrating than betas per se. Shielding composed of materials with lower atomic weight generates gammas with lower energy, making such shields somewhat more effective per unit mass than ones made of larger atoms such as lead. Being composed of charged particles, beta radiation

8690-592: The mitotic cycle the cell is when the irradiation occurs. If the cell is in interphase , while it is still a single strand of chromatin, the damage will be replicated during the S1 phase of the cell cycle , and there will be a break on both chromosome arms; the damage then will be apparent in both daughter cells . If the irradiation occurs after replication, only one arm will bear the damage; this damage will be apparent in only one daughter cell. A damaged chromosome may cyclize, binding to another chromosome, or to itself. Diagnosis

8800-459: The mode from X to E. She did so and pressed ↵ Enter to go down to the command box. As "Beam ready" was displayed, she pressed P (Proceed : continue). The machine produced a loud noise, which was heard through the intercom. Error 54 was displayed. The operator entered the room and the patient described a burning sensation on his face. The patient died on May 1, 1986, just shy of 3 weeks later. The autopsy showed severe radiation damage to

8910-492: The neutron-rich fission byproducts produced in nuclear reactors . Free neutrons also decay via this process. Both of these processes contribute to the copious quantities of beta rays and electron antineutrinos produced by fission-reactor fuel rods. Unstable atomic nuclei with an excess of protons may undergo β decay, also called positron decay, where a proton is converted into a neutron, a positron , and an electron neutrino : Beta-plus decay can only happen inside nuclei when

9020-450: The others are measured in sieverts (in SI, unit symbol Sv ) or rem (in CGS). 1 rad = 0.01 Gy and 1 rem = 0.01 Sv. In most of the acute exposure scenarios that lead to radiation sickness, the bulk of the radiation is external whole-body gamma, in which case the absorbed, equivalent, and effective doses are all equal. There are exceptions, such as the Therac-25 accidents and

9130-429: The patient showed burns on the skin in the area. Four days later the reddening of the area had a banded pattern similar to that produced in the incident the previous year, and for which they had not found the cause. The AECL began an investigation, but was unable to reproduce the event. The hospital physicist conducted tests with film plates to see if he could recreate the incident, which involved two X-ray parameters with

9240-418: The patients with approximately 100 times the intended dose of radiation, and over a narrower area, delivering a potentially lethal dose of beta radiation . The feeling was described by patient Ray Cox as "an intense electric shock", causing him to scream and run out of the treatment room. Several days later, radiation burns appeared, and the patients showed the symptoms of radiation poisoning ; in three cases,

9350-462: The pattern of bacterial susceptibility and nosocomial infections in the affected area and medical center and the degree of neutropenia. Broad-spectrum empirical therapy (see below for choices) with high doses of one or more antibiotics should be initiated at the onset of fever. These antimicrobials should be directed at the eradication of Gram-negative aerobic bacilli (i.e., Enterobacteriaceae , Pseudomonas ) that account for more than three quarters of

9460-406: The phosphor, causing the phosphor to give off photons , much like the cathode-ray tube in a television. The illumination requires no external power, and will continue as long as the tritium exists (and the phosphors do not themselves chemically change); the amount of light produced will drop to half its original value in 12.32 years, the half-life of tritium. Beta-plus (or positron ) decay of

9570-464: The primary cause to generally poor software design and development practices, rather than singling out specific coding errors. In particular, the software was designed so that it was realistically impossible to test it in a rigorous, automated way. Researchers who investigated the accidents found several contributing causes. These included the following institutional causes: The researchers also found several engineering issues: Leveson notes that

9680-429: The radiation dose. This is not always the case, however; care should be taken when constructing shielding for a specific purpose. For example, although high atomic number materials are very effective in shielding photons , using them to shield beta particles may cause higher radiation exposure due to the production of bremsstrahlung x-rays, and hence low atomic number materials are recommended. Also, using material with

9790-432: The radiation room was offline and the intercom had been broken that day. With the first dose the patient felt an electric shock and heard a crackle from the machine. Since it was his ninth session, he realized that it was not normal. He started to get up from the table to ask for help. At that moment the operator pressed P to continue the treatment. The patient felt a shock of electricity through his arm, as if his hand

9900-447: The reasons why radiation overdose was impossible on the Therac-25, stating both machine failure and operator error were not possible. Six months later, the patient developed chronic ulcers under the skin due to tissue necrosis. She had surgery and skin grafts were placed. The patient continued to live with minor sequelae . Over two years, this hospital treated more than 500 patients with the Therac-25 with no incident. On March 21, 1986,

10010-404: The remainder of the energy is carried by the nearly undetectable electron antineutrino . In comparison to other beta radiation-emitting nuclides, the electron is moderately energetic. It is blocked by around 1 m of air or 5 mm of acrylic glass . Of the three common types of radiation given off by radioactive materials, alpha , beta and gamma , beta has the medium penetrating power and

10120-414: The right temporal lobe and brain stem. The hospital physicist stopped the machine treatments and notified the AECL. After strenuous work, the physicist and operator were able to reproduce the error 54 message. They determined that speed in editing the data entry was a key factor in producing error 54. After much practice, he was able to reproduce the error 54 at will. The AECL stated they could not reproduce

10230-516: The source of the burn had passed through her, which is the case with radiation burns. The staff at the treatment center did not believe it was possible for the Therac-25 to cause such an injury, and it was treated as a symptom of her cancer . Later, the hospital physicist consulted the AECL about the incident. He calculated that the applied dose was between 15,000 and 20,000 rad (radiation absorbed dose) when she should have been dosed with 200 rad. A dose of 1000 rad can be fatal. In October 1985, Katie sued

10340-542: The syndrome in the weeks and months following the Hiroshima and Nagasaki bombings. Sasaki and his team were able to monitor the effects of radiation in patients of varying proximities to the blast itself, leading to the establishment of three recorded stages of the syndrome. Within 25–30 days of the explosion, Sasaki noticed a sharp drop in white blood cell count and established this drop, along with symptoms of fever, as prognostic standards for ARS. Actress Midori Naka , who

10450-457: The three components of time, distance, and shielding. The longer that humans are subjected to radiation the larger the dose will be. The advice in the nuclear war manual entitled Nuclear War Survival Skills published by Cresson Kearny in the U.S. was that if one needed to leave the shelter then this should be done as rapidly as possible to minimize exposure. In chapter 12, he states that "[q]uickly putting or dumping wastes outside

10560-458: The thyroid gland, their effectiveness is still highly dependent on the time of ingestion, which would protect the gland for the duration of a twenty-four-hour period. They do not prevent ARS as they provide no shielding from other environmental radionuclides. If an intentional dose is broken up into a number of smaller doses, with time allowed for recovery between irradiations, the same total dose causes less cell death . Even without interruptions,

10670-611: The tissue showing the syndrome itself be exposed (e.g., gastrointestinal syndrome is not seen if the stomach and intestines are not exposed to radiation). Some areas affected are: Early symptoms of ARS typically include nausea, vomiting, headaches, fatigue, fever , and a short period of skin reddening . These symptoms may occur at radiation doses as low as 0.35 grays (35 rad). These symptoms are common to many illnesses, and may not, by themselves, indicate acute radiation sickness. A similar table and description of symptoms (given in rems , where 100 rem = 1 Sv ), derived from data from

10780-466: The turntable in field-light position. The film appeared to match the film that was left by mistake under the patient during the accident. It was found the patient was exposed to between 8,000 and 10,000 rad instead of the prescribed 86 rad. The patient died in April 1987 from complications due to radiation overdose. The relatives filed a lawsuit that ended with an out-of-court settlement. A commission attributed

10890-411: The turntable was in the correct position before starting treatment. In the Therac-25, these were replaced by software checks. The six documented accidents occurred when the high-current electron beam generated in X-ray mode was delivered directly to patients. Two software faults were to blame. One was when the operator incorrectly selected X-ray mode before quickly changing to electron mode, which allowed

11000-410: The two conditions exist. Individuals that develop neutropenia after exposure to radiation are also susceptible to irradiation damage in other tissues, such as the gastrointestinal tract, lungs and central nervous system. These patients may require therapeutic interventions not needed in other types of neutropenic patients. The response of irradiated animals to antimicrobial therapy can be unpredictable, as

11110-624: The world, the Soviet nuclear program involved human experiments on a large scale, which is still kept secret by the Russian government and the Rosatom agency. The human experiments that fall under intentional ARS exclude those that involved long term exposure . Criminal activity has involved murder and attempted murder carried out through abrupt victim contact with a radioactive substance such as polonium or plutonium . The most commonly used predictor of ARS

11220-438: Was also more economical for a hospital to have a dual machine that could apply treatments of electrons and X-rays, instead of two machines. The Therac-25 was designed as a machine controlled by a computer, with some safety mechanisms switched from hardware to software as a result. AECL decided not to duplicate some safety mechanisms, and reused modules and code routines from the Therac-20 for the Therac-25. The first prototype of

11330-446: Was evident in experimental studies where metronidazole and pefloxacin therapies were detrimental. Antimicrobials that reduce the number of the strict anaerobic component of the gut flora (i.e., metronidazole) generally should not be given because they may enhance systemic infection by aerobic or facultative bacteria , thus facilitating mortality after irradiation. An empirical regimen of antimicrobials should be chosen based on

11440-399: Was found to have absorbed about 9.46 grays (Gy) of ionizing radiation. The doses at the hypocenters of the Hiroshima and Nagasaki atomic bombings were 240 and 290 Gy, respectively. Cutaneous radiation syndrome (CRS) refers to the skin symptoms of radiation exposure. Within a few hours after irradiation, a transient and inconsistent redness (associated with itching ) can occur. Then,

11550-404: Was moving or in the treatment position. Afterward, the AECL claimed that the modifications represented a five-order-of-magnitude increase in safety. In December 1985 a woman developed an erythema with a parallel band pattern after receiving treatment from a Therac-25 unit. Hospital staff sent a letter on January 31, 1986, to the AECL about the incident. The AECL responded in two pages detailing

11660-415: Was not activated at the time of treatment and there was no record of the applied radiation data. An out-of-court settlement was reached to resolve the lawsuit. The Therac-25 had been in operation in the clinic for six months when, on July 26, 1985, a 40-year-old patient was receiving her 24th treatment for cervical cancer . The operator activated the treatment, but after five seconds the machine stopped with

11770-808: Was present during the atomic bombing of Hiroshima, was the first incident of radiation poisoning to be extensively studied. Her death on 24 August 1945 was the first death ever to be officially certified as a result of ARS (or "Atomic bomb disease"). There are two major databases that track radiation accidents: The American ORISE REAC/TS and the European IRSN ACCIRAD. REAC/TS shows 417 accidents occurring between 1944 and 2000, causing about 3000 cases of ARS, of which 127 were fatal. ACCIRAD lists 580 accidents with 180 ARS fatalities for an almost identical period. The two deliberate bombings are not included in either database, nor are any possible radiation-induced cancers from low doses. The detailed accounting

11880-485: Was reported to the FDA and the Canadian Radiation Protection Bureau. The AECL suspected that there might be an error with three microswitches that reported the position of the turntable. The AECL was unable to replicate a failure of the microswitches and microswitch testing was inconclusive. They then changed the method to be tolerant of one failure and modified the software to check if the turntable

11990-420: Was stopped, the aperture was opened to 35 cm × 35 cm and a dose of 3 rad was administered. The machine stopped. The operator entered the room to remove the film plates and adjust the patient's position. He used the hand control inside the room to adjust the turntable. He left the room, forgetting the film plates. In the control room, after seeing the "Beam ready" message, he pressed the B key to fire

12100-413: Was torn off. He reached the door and began to bang on it until the operator opened it. A physician was immediately called to the scene, where they observed intense erythema in the area, suspecting that it had been a simple electric shock. He sent the patient home. The hospital physicist checked the machine and, because it was calibrated to the correct specification, it continued to treat patients throughout

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