test 4, Ch 9 Stochastic effects and late tissue reactions in systems

Stages of Gestation in Humans: All life forms are most vulnerable to radiation during embryonic state of development Period of gestation during which embryo-fetus is exposed governs effects (death or congenital abnormality) of radiation Three stages of gestation in humans:

(1)Preimplantation - 0-9 days after conception (2)Organogenesis- 10 days to 12 weeks post conception (3)Fetal stage - extends from 12 weeks to term

Epidemiologic data about the Hiroshima atomic bomb survivors

--Indicate the chance of contracting leukemia as a result of exposure to radiation is directly proportional to the magnitude of the radiation exposure --Radiation-induced leukemia is assumed to follow a linear nonthreshold dose-response relationship compared with leukemia in a population that has not been exposed to ionizing radiation. --More recent reevaluation of the quantity and type of radiation that was released in the cities of Hiroshima and Nagasaki provides a better foundation for radiation dose and damage assessment. -Originally, neutrons were credited with the damage in Hiroshima. -Recent studies revealed that the uranium-fueled bomb dropped on Hiroshima provided more gamma radiation exposure and less neutron exposure than previously believed, data on the survivors were updated to reflect this more accurate information. -Inhabitants of Nagasaki, who were exposed to a plutonium bomb, received only 10% of their exposure from neutrons and 90% from gamma radiation. -Based on the revised atomic bomb data, radiation-induced leukemias and solid tumors in the survivors may be attributed predominantly to gamma radiation exposure. Impact of atomic bomb dosimetry revision, There is a significant increase in cancer risk estimates for both gamma and X-radiation.

Embryonic Effects Resulting from the Chernobyl Nuclear Power Plant Accident: Of the 135,000 evacuees from 18-mile radial zone about 2000 were pregnant and received an average total-body EqD of 0.43 Sv

--No obvious abnormalities were observed in the 300 live babies born in August 1987 --However, from after 1987 through 1990 there was an increased number of miscarriages, premature births, and stillbirths --Also there was an increase to 3x the normal rate of deformities and developmental abnormalities in newborns

How scientists use epidemologic studies to predict the risk of cancer in human populations exposed to low doses

--The incident rates at which radiation induced cancers occur are determined by comparing the natural incidence of cancer occurring in a population with the incidence of cancer occurring in an irradiated population. --Risk factors are then determined for the general human population. --Radiobiologists use information from these epidemiologic studies to formulate dose response estimates to predict the risk of cancer in human populations exposed to low doses of ionizing radiation

Continued use of the linear dose-response model for radiation protection standards

--has the potential to exaggerate the seriousness of radiation effects at lower dose levels from low-LET radiation. --It accurately reflects the effects of high-LET radiation (neutrons and alpha rays) at higher doses.

Nonthreshold

--indicates that a radiation absorbed dose of any magnitude has the capability of producing a biologic effect. --For the linear nonthreshold curve biologic effect responses will be caused by ionizing radiation in living organisms in a directly proportional manner all the way down to dose levels approaching zero. --No radiation dose can be considered absolutely safe with the severity of the biologic effects increasing directly with the magnitude of the absorbed dose. -- no known level of radiation dose exists below which the chance of sustaining biologic damage is zero

Second and Third Trimesters of Pregnancy:

--lesser numbers of cells are differentiating --However congenital abnormalities and functional disorders such as sterility may be caused by radiation exposure during this time --Evidence for radiation-induced congenital abnormalities comes from 4 decades of follow-up studies of children exposed in utero during Hiroshima and Nagasaki

identify ionizing radiation exposed human populations or groups that prove radiation induces cancer

-Laboratory experiments with animals and statistical studies of human populations (e.g. Japanese atomic bomb survivors) exposed to ionizing radiation prove that radiation induces cancer. -In humans, this may take 5 or more years to develop -The physical appearance of cancer induced by ionizing radiation does not appear different than a cancer caused by other agents. -Cancer caused by low-level radiation is difficult to identify. -Human evidence of radiation carcinogenesis comes from epidemiologic studies conducted many years after subjects were exposed to high doses of ionizing radiation.

explain why regulatory agencies (Committee on the Biological Effects of Ionizing Radiation (BEIR) 1980) continue to use the linear dose-response model for establishing radiation protection standards

-Revised risk estimates indicated that the risk of radiation exposure was about three to four times greater that previously projected. -Currently the committee recommends the use of the linear nonthreshold curve of radiation dose-response for most types of cancer. -linear-quadratic nonthreshold curve (LQNT) curve implies that the biologic response to ionizing radiation is directly proportional to the dose received. --is a more accurate reflection of stochastic somatic and genetic effects at low-dose levels from low-LET radiation. Leukemia, breast cancer, and heritable damage are presumed to follow the LQNT curve.

Embryonic Cell Radiosensitivity during the First Trimester of Pregnancy

Embryonic cells begin dividing and differentiating after conception, and are extremely radiosensitive and therefore be easily damaged by exposure to ionizing radiation.

Radiation Induced Injuries: Japanese Atomic Bomb Survivors. Data Obtained from Epidemiologic Studies:

Epidemiologic studies of about 100,000 A-bomb indicate that ionizing radiation causes leukemia (proliferation of the white blood cells) "Studies of the atomic bomb survivors in both Hiroshima and Nagasaki show a statistically significant increase in leukemia incidence in the exposed population compared with the non-exposed population. In the period 1950 to 1956, 117 new cases of leukemia were reported in the Japanese survivors; approximately 64 of these can be attributed to radiation exposure."

Children of the Marshall Islanders:

Fallout from an a-bomb test on Bikini Atoll in March, 1954: Wind shifted and carried the fallout over the neighboring islands. Children on neighboring islands received substantial absorbed doses to thyroid from external and internal exposures: Thyroid cancers Average doses:12 Gyt (1200 rad)

Early Medical Radiation Workers:

First generation radiation workers (radiologists, dentists, radiographers) Exposed to large amounts of radiation—more than 1 Gy/yr: Developed cancerous skin lesions Early radiologists showed higher incidence of aplastic anemia and leukemia. No increase in adverse health effects for workers who began careers after 1940. This is because of increased knowledge and use of proper protective measures and improved safety devices.

"The most frequent mutations in man are not those leading to freaks or obvious hereditary diseases, but those causing minor impairments leading to higher embryonic death rates, lower life expectancy, increase in disease, or decreased fertility"

From J.F. Crow, geneticist who spent many years experimenting with fruit flies

discuss the concept and process radiation induced genetics effects

Genetic (hereditary) effects - biologic effects on future generations They can occur as a result of radiation induced damage to DNA molecule in sperm or ova of an adult leading to germ cell mutations. These cause faulty genetic information to be transmitted to the offspring. The altered hereditary information may manifest as various diseases or malformations

Late somatic effects consequences of radiation exposure that appear months or years after such exposure Late effects may be stochastic or tissue reactions. Stochastic effects (such as cancer) usually requires years to be noticeable in a population.

.

Mutant genes cannot properly run the cell's normal chemical reactions or properly control the sequence of amino acids in the formation of specific proteins These incapacities result in various genetic diseases. Ex: sickle cell anemia arises from the defective synthesis of the protein hemoglobin. About 300 amino acids combine to form the hemoglobin molecule. Sickle cell anemia is caused by the omission of only a single vital amino acid.

.....

During preimplantation stage (0 to 9 days): Fertilized ovum divides and forms a ball-like structure containing undifferentiated cells If this is irradiated with a dose in the range of

0.05 to 0.15 Gyt embryonic death will occur Malformations do not occur at this stage (bc death occurs)

Radiation doubling equivalent dose for humans as determined from studies of offspring of a-bomb survivors of Hiroshima and Nagasaki is estimated to have a mean value of

1.56 Sv This is based on the genetic indicators of untoward pregnancy outcome

Hereditary disorders are common in any animal population. In humans, a hereditary disorder is present in about _____ all live births in US.

10%

Radium Watch-Dial Painters:

1920's-30's pointed their radium containing brush tips with lips Radium chemically similar to calcium and accumulated in bones Caused: Osteoporosis Osteogenic sarcoma Other malignancies: Carcinoma of epithelial lining of nasopharynx and paranasal sinuses Doses of 5 Gyt or more are assumed to have caused malignancies. Of 1474 women - 61 were diagnosed with cancer of the paranasal sinuses and 21 with cancer of the mastoids studies attributed the death of at least 18 of workers to radium poison

Patients injected with Contrast Agent Thorotrast:

1925 to 1945 used for angiography and contained radioactive suspension. Radioactive material emitted alpha particles and were deposited in patient's reticuloendothelial system: Liver and spleen were primary recipients: After a period of 15 to 20 years Liver and spleen cancer Angiosarcomas Biliary duct carcinomas Extravascular injections caused: Tissue surrounding injection site became cancerous

Infants treated for Enlarged Thymus Gland:

1940's-50's infants were treated with therapeutic doses (1.2 to 6.0 Gyt) of x-radiation to reduce size of gland. Resulted in development 20 years later of thyroid nodules and carcinoma in many of these treated patients.

Uranium Miners:

50% European miners extracting uranium developed lung cancer after inhaling radon. In US, Navajo people mined uranium and sustained lethal doses of ionizing radiation by breathing radioactive dust and drinking radioactive water Died from cancer and respiratory diseases Family members also developed radiation induced cancers from contaminated clothes of miners. Estimated dose about 10 Sv or more.

The developing fetus is most susceptible to radiation induced congenital abnormalities during organogenesis (10 days to 12 weeks) This the time when the undifferentiated cells are beginning to differentiate into organs

Abnormalities occurring from irradiation during organogenesis may include: growth inhibition Intellectual disability microcephaly genital deformities sense organ damage During the late stages of organogenesis, the presence of nonminor abnormalities in the fetus will cause neonatal death (death at birth)

Risk Model Used to Predict High-Dose Cellular Response Biologic response does not occur below a specific dose level. Laboratory experiments on animals and data from human populations observed after acute high doses of radiation provided the foundation for this curve.

Acute reactions from significant radiation exposure such as skin erythema and hematologic depression may be demonstrated graphically through the use of a linear threshold dose-response curve.

Tissue reactions

Any radiation effects on organ or organ systems that increase with increasing dose and below which the effect rarely or never occurs. They may occur as early effects, immediately after irradiation, or late effects, after some latent period.

various dose-response relationships

As dose increases so do most effects. --Curve can be: Linear - straight line or Non-linear-curved to some degree And depicts: Threshold dose or Non-threshold dose

Exposure to ionizing radiation may cause cancer as a stochastic effect

At high doses (e.g. atomic bomb survivors), the risk is measurable in exposed human populations.

Risk estimates to predict cancer incidence may be given in terms absolute risk or relative risk caused by a specific exposure to ionizing radiation (over and above background exposure)

Both models predict the number of excess cancers, or cancers that would not have occurred in the population in question without the exposure to ionizing radiation.

International Chernobyl Project: Was initiated in 1990 in response to a request for assistance from the former Soviet Union Study compared seven contaminated Russian villages with six uncontaminated villages.

By 1990 no significant increases in fetal and genetic abnormalities were seen in this population --Because of relatively long latency period for radiogenic cancer, particularly solid tumors researchers expect that more time will be required to determine ultimate impact on population --Estimates of as many as 500 excess cancers in former Soviet Union during the next 50-60 years have been made.

Effects of Low-Level Ionizing Radiation on Embryo-Fetus:

Can only be poorly estimated Documentation of the effects of low-level radiation on the embryo-fetus irradiated in utero, is insufficient because some types of abnormality occur in a small percentage (about 4%) of all live births in the US However, if the exposure occurs during a period of major organogenesis, the abnormality and its occurrence may be more pronounced. --human genes vary naturally and the expression of the traits they encode is affected by the enviornment

Lab experiments on animals and studies on human populations exposed to high doses of radiation from various causes were conducted to collect information about the occurrence and degree of adverse health effects. Using this data it was determined that three categories of harmful health consequences also require study at low dose levels

Cancer induction Damage to the unborn from irradiation in utero Genetic (hereditary) effects

Three major types of late effects

Carcinogenesis Cataractogenesis Embryologic effects (birth defects) (Carcinogenesis and embryonic effects are considered stochastic effects, and cataractogenesis is regarded as a late tissue reaction)

damage in the living organism as a whole further on in life. These late effects are the long-term results of radiation exposure. Examples of measurable late biologic damage (months or years after exposure to ionizing radiation)

Cataracts Leukemia Genetic mutations

Low-Level Effects Summary

Cells that survive the initial irradiation may have incurred some form of damage. Theoretically, radiation damage to just one or a few cells of an individual could actually produce a stochastic effect such as a malignancy or a hereditary disorder many years after radiation exposure. Tissue reactions such as skin reactions do not usually demonstrate a late onset. Extreme reactions associated with high skin doses may persist for some time, but will usually occur in weeks or months after the exposure.

Some data come from test groups of children conceived after one or both parents had been exposed to a-bomb detonation in Hiroshima or Nagasaki As of third generation, no radiation-induced genetic effects are known but

Does not mean effects will not be seen in subsequent generations

Incidence of Breast Cancer in Radiation Treatment of Benign Postpartum Mastitis:

In a particular study, 531 women received a mean dose of 247 cGyt: "Breast cancer doubled from 3.2% expected to 6.3% actual" Epidemiologic statistical studies ongoing for screening and diagnostic exams

Natural incidence of breast cancer

In general, Japanese women have a lower incidence of breast cancer than U.S. and Canadian women.

Incidence of Leukemia Rate of Other Radiation-Induced Malignancies Among Japanese Atomic Bomb Survivors

Incidence of leukemia has slowly declined since the late 1940s and early 1950s. Occurrence rates of other radiation-induced malignancies have continued to escalate since the late 1950s and early 1960s including: Thyroid cancer Breast cancer Lung cancer Bone cancer

American Radiologic Technologists:

Initiated in 1982 still in progress -Study of approximately 146,000 US radiologic technologists: -Evaluating potential radiation-related health effects from long-term, repeated exposures to low-dose radiation: Cancer incidences and other work-related condition -Involves a series of mail surveys to all participating technologists and phone surveys with about 1200 retired radiographers in the field before 1950. -Among 90,305 technologists who completed first survey in mid-1980s there were 1283 deaths from cancer -Comparison was made between technologists who started working in 1960s or later and those who began working before 1940 -A slightly higher risk of dying from any type of cancer was found in technologists working before 1940 -Technologists working after 1940 did not demonstrate elevated risk.

Attempts by Physicians to Prevent Thyroid Cancer in Children:

Iodine 131 (131I ) one of radioactive materials in plume -Concentrates in thyroid and may cause cancer many years later -Administered postassium iodide to children in Poland and other countries -Potassium iodide blocks uptake of 131I . Degree of effectiveness remains to be determined -In other accidently exposed populations thyroid cancer has occurred in some individuals at doses of 1 Gy (100 rad) or less—approximate time for appearance of thyroid malignancies is usually 10-20 years after exposure

Agents that can increase the frequency of mutations. These agents are called mutagens. Ionizing radiation is one of the more effective mutagens known.

Ionizing radiation Viruses Specific chemicals

Life Span Shortening, Animal Studies

Laboratory experiments on small animals have shown the life span of animals that were exposed to nonlethal doses of ionizing radiation was shortened as a result of the exposure. -When compared with a control group of unexposed small animals, the exposed animals died sooner. -This reduction was termed nonspecific life span shortening. It was also believed that radiation accelerated the aging process. -In reality, early demise of the experimental animals resulted from the induction of cancer.

Cancer is the most important late stochastic effect caused by exposure to ionizing radiation. This effect is a random occurrence that does not seem to have a threshold and for which the severity of the disease is not dose-related.

Leukemia induced by a low-dose exposure is no different from a person's leukemia that was caused by a high-dose exposure.

Human Studies: American Radiologists:

Life span studies of American radiologists made by RSNA from 1945-1954 revealed radiologists did have a shorter life span than nonradiologist physicians. --However...process of evaluation has been subject to criticism and conclusions of study are questionable --Further analysis of epidemiologic studies showed shortening of life span in both animals and humans was the result of cancer and leukemia and not other "nonspecific" causes or accelerated aging.

describe the concept of risk for radiation-induced malignancies and explain the models that are used to give risk estimates

Low-level doses are a consideration for patients and personnel exposed to ionizing radiation as a result of diagnostic imaging procedures. -The risk estimate for humans contracting cancer from low-level radiation exposure is still controversial. -No conclusive proof exists that low-level ionizing radiation exposure below 0.1 Gy cause a significant increase in the risk of malignancy. -Risk may be negligible or even nonexistent

Stochastic effects "probabilistic effects" These effects occur months or years after high level, and possibly also after low level, radiation exposure. Examples include cancer and genetic effects.

Mutational or randomly occurring biologic changes, independent of dose, in which the chance of occurrence of the effect rather than the severity of the effect is proportional to the dose of ionizing radiation.

Late tissue reactions-

Nongenetic consequences of radiation exposure

Chernobyl Nuclear Disaster, Need for follow-up studies. 1986 accident requires long term follow up studies to assess magnitude and severity of late effects.

Observations investigating potential increases in the incidence of leukemia, thyroid problems, breast cancer, and other possible radiation induced malignancies will continue

Relative Risk Model:

Predicts that the number of excess cancers will increase as the natural incidence of cancer increases with advancing age in a population.

At low equivalent doses, below 0.1 Sv, which includes groups such as occupationally exposed individuals and virtually all patients in diagnostic radiology, this risk is not directly measurable in population studies.

Reasons: The risk is overshadowed by other causes of cancer in humans. The risk is zero.

cataracts

Recent data tend to show that the threshold for cataract induction is lower than was previously thought. The threshold for single exposures is now considered to be 0.5Gy (50 cGy)

Epidemiology

Science that deals with the incidence, distribution, and control of disease in a population. Epidemiologic studies consist of observations and statistical analysis of data, such as the incidence of disease within groups of people. Studies include the risk of radiation-induced cancer

The classification of somatic effects(living organisms that have been exposed to radiation sustain biologic damage) may be subdivided into

Stochastic effects: The probability that the effect happens depends term-30 upon the received dose, but the severity of the effect does not. Example: Occurrence of cancer Tissue reactions: Both the probability and the severity of the effect depend upon the dose. Example: A cataract

Radiation-induced breast cancer

Studies of the female Japanese atomic bomb survivors provide strong evidence that ionizing radiation can induce breast cancer. Incidence of breast cancer in these women rises with radiation dose. Numerous studies of female survivors indicate a relative risk for breast cancer ranging from 4:1 to as high as 10:1.

pic. Nominal risk of malignancy from a dose of 0.01 Gyt of uniform whole-body radiation

The graph indicates that leukemia occurs about 2 years after the initial exposure, rises to its highest level of incidence between 7 and 10 years, and then declines to almost zero at about 30 years. Unlike leukemia, solid tumors take about 10 years to develop and generally increase in occurrence at the same rate that cancer increases as people age. Whether the risk for solid tumors continues to rise beyond 40 years or declines, as with leukemia, is still unknown. Follow-up studies of atomic bomb survivors may eventually prove the answer.

Why Early Studies Did Not Demonstrate a Significant Increase in Incidence of Leukemia after Accident: Subsequent Findings:

The study of Japanese atomic bomb survivors demonstrated that radiation causes leukemia and the disease is assumed to follow a linear nonthreshold dose-response curve. -Early studies of Chernobyl victims did not demonstrate a significant increase in the incidence of leukemia -Possible reason was because the radioactive iodine and cesium released during the accident may produce damaging health issues in different ways. I131 assimilates in the thyroid -Radioactive cesium has a longer life and causes whole-body irradiation over a lengthy time span through its long term presence in the environment and the food supply. This probably increases the incidence of childhood leukemia. This increase is difficult to detect without very sensitive and reliable monitoring procedures

Cataractogenesis

There is a high probability that a single dose of approximately 2 Gyt will induce the formation of cataracts. Cataracts result in partial or complete loss of vision laboratory experiments with mice show that cataracts may be induced with doses as low as 0.1 Gyt -Evidence of human radiation cataractogenesis comes from observation of small groups of people who accidently received substantial doses to the eyes and include: Japanese atomic bomb survivors Nuclear physicists working with cyclotrons (units that produce beams of high energy particles such as 150 MeV proton beams) between 1932 and 1960 Patients undergoing radiation therapy who have received significant exposure to the eyes during treatment

explain the doubling dose concept and give an example of how the number of mutations increases as dose increases --Animal studies of radiation induced hereditary changes led to the development of the doubling dose concept

This dose measures the effectiveness of ionizing radiation to cause mutations. Doubling dose - The radiation dose that causes the number of spontaneous mutations occurring in a given generation to increase to two times their original number Example: If 7% of offspring in each generation are born with mutations in the absence of radiation other than background levels, the administration of the doubling dose to all members of the population would eventually increase the number of mutations to 14 %.

Threshold relationship

Threshold is defined as a point or level at which a response or reaction to an increasing stimulation first occurs. means that below a certain radiation level or dose, no biologic effects are observed. Biologic effects are observed only when the threshold level or dose is reached.

Incidence of Thyroid Cancer and Breast Cancer since Accident: During first 10 years after disaster:

Thyroid cancer increased dramatically among children living in regions where heaviest radioactive iodine contamination occurred "most pronounced health effect" of radiation accident As of April 1996, more than 700 cases of thyroid cancer were diagnosed in children residing in high contamination area—by 1998 a total of 1700 cases has been diagnosed. Significantly higher than expected may be other contributing factors such as chronic iodine deficiency in the children; and Genetic predisposition to developing thyroid cancer after radiation exposure

Tissue reactions, such as skin effects may be noticeable sooner, although months or more may be required for the full expression.

Tissue reactions are the result of slowly developing changes to body tissues that may be modified by other factors, such as medical intervention after exposure

Japanese Atomic Bomb Survivors: Hiroshima-August 6, 1945 Nagasaki-August 9, 1945

Total population 300,000 88,000 killed (heat & blast) 70,000 injured Many survivors became victims of radiation injuries Since then survivors have been observed for stochastic late somatic effects

Review of Fetal Effects by UNSCEAR:

United Nations Scientific Committee on Effects of Atomic Radiation Reviewed following fetal effects: mortality, induction of malformations, intellectual disability and childhood cancer

Current radiation protection philosophy:

Utilizes the linear nonthreshold dose-response relationship (LNT model) and assumes that risk still exists May be determined by extrapolating from high-dose data, in which the risk has been directly observed, down to the low doses, in which it has not been observed (a controversial concept)

Worldwide Effects of the Accident: chernobyl

Winds carried plume in different directions during 10 days following accident More than 20 countries received fallout as a consequence. About 400,000 people received exposure to fallout: Harvard study estimates "that about 20,000 people throughout the

Such sources of low-level radiation exposure include: ""an absorbed dose of 0.1 Sv or less delivered over a short period of time" and as "a larger dose delivered over a long period of time—for instance 0.5 Sv in ten years.""

X-rays and radioactive materials used for diagnostic purposes Employment related exposure in medicine and industry Natural background exposures

In order for recessive mutation to appear in offspring

both parents must have same genetic defect. This means the defect must be located on the same part of a specific DNA base sequence in each parent -this rarely occurs the effects of recessive mutations are not likely to appear in a population.

spontaneous mutations - mutations in genetic material occur spontaneously without a known cause

can be transmitted from one generation to the next and cause a wide variety of disorders or disease and include: Hemophelia Huntington's chorea Down syndrome Duchenne's muscular dystrophy Sickle cell anemia Cystic fibrosis Hydrocephalus

differentiate between dominate and recessive gene mutations

dominant -probably expressed in offspring recessive probably not expressed for several generations

Cancer and functional disorders during childhood are other possible effects of irradiation

during the fetal stage (week 12 to term)

A non-somatic effect is an

effect in offspring of the individual who was irradiated. Example: irradiation of genetic material (sperm or eggs) leading to a genetic malformation in offspring

The EfD of a typical routine two-view CXR is about 0.06 mSv (6 mrem) (depending on habitus)

far below what is considered low-level exposure.

Absolute Risk Model

forecasts that a specific number of malignancies will occur as a result of exposure

The only concrete evidence showing that ionizing radiation causes genetic effects comes with extensive experimentation with fruit flies and mice at high radiation doses Data on mice may be extrapolated to low doses and then applied to humans This information obtained from the fruit fly experiments indicates tha

hereditary (genetic) effects do not have a threshold. there is no such thing as a "100% safe" gonadal radiation dose. This implies that even the smallest radiation dose could cause some genetic damage.

purpose of radiation dose-response curve

maps the observed effects of radiation exposure in relation to the dose of radiation received. --Information obtained can be used to attempt to predict the risk of occurrence of malignancies in human populations that have been exposed to low levels of ionizing radiation. --may also be the severity of an effect, such as the severity of cataracts as dose increases.

First trimester seems to be

most crucial period for irradiation of embryo-fetus because a large number of stem cells are present during this period of gestation

Because the developing CNS and related sensory organs of the embryo fetus contain a large number of stem cells, the first trimester of pregnancy is the

most crucial period with regard to harmful consequences from irradiation

UNSCEAR study in 2001 on hereditary effects of radiation concluded that

no radiation induced genetic diseases have so far been demonstrated in human populations exposed to ionizing radiation.

Cataracts are considered to be a late tissue reaction (deterministic) that is

non-random

A high dose of radiation received by the embryo within about 2 weeks of fertilization (before the start of organogenesis),

prenatal death is the most obvious consequence. Usually manifests as a spontaneous abortion

The sigmoid, or S-shaped (nonlinear), threshold curve is generally employed in

radiation therapy to demonstrate high-dose cellular response to radiation within specific locations, such as skin, lens of the eye, and various types of blood cells. --The tail of the curve indicates limited recovery occurs at lower radiation doses --At the highest radiation dose, the curve gradually levels off and veers downward because the affected living specimen or tissue dies before the observable effect appears.

Leukemia and genetic effects are stochastic effects and are

random consequences that, if they appear, do not do so for extended periods.

Radiation is thought to cause primarily

recessive mutations

However some very lengthy fluoroscopic procedures can result in "not insignificant" radiation exposure to the lens of the eye from cumulative scatter radiation. Occupational dose can be

substantially reduced when occupational workers wear protective eyewear..

Even at the relatively high doses received by the Japanese atomic bomb survivors

the probability of an excess fatal cancer begin cause is low—approximately 5% per sievert

Radiation-induced cataracts in humans follow a

threshold, nonlinear dose-response relationship

1989 BEIR V report supported the linear-quadratic model for leukemia only For all other cancers the BEIR V Committee recommended adoption of the linear model to fit the available data.

true

Any nonlethal radiation dose received by the germ cells can cause chromosome mutations that may be transmitted to successive generations.

true

Epidemiologic studies suggest that although the radiation doses encountered in diagnostic radiology should be considered, the benefit to the patient of the information gained from an imaging procedure greatly exceeds the minimal theoretical risk to the patient for developing cancer as a late stochastic response to radiation exposure.

true

Evacuation of people within 36 hours after the accident. Of the 135,000 evacuees about 24,000 people received an equivalent dose of about 0.45 Sv. The remaining 111,000 people received from 0.03 to 0.06 Sv. If the evacuees are monitored for at least 30 years, important estimates of radiation-induced leukemias, thyroid cancers and other malignancies may be obtained. (t/f)

true

Medical physicists are able to make fetal dose estimates for specific patients based upon factors such as patient size and technical factors in cases where there are concerns about medical management. (t/f)

true

Some advocates, who agree that no radiation level is absolutely safe, theorize that because all radiation exposure levels possess the potential to cause biologic damage, radiographers must never fail to employ aggressive radiation safety measures whenever humans are exposed to radiation during diagnostic imaging procedures.

true

Stochastic effects (e.g., cancer) and hereditary effects at low-dose levels from low-LET radiation, such as the type of energy used in diagnostic radiology, appear to follow a linear-quadratic nonthreshold curve.

true.

There is no current evidence of radiation induced genetic effects in persons employed in diagnostic imaging or in patients undergoing radiologic exams Even with this information, gonadal shielding must be effectively used and all radiation exposure must be maintained ALARA to minimize the possibility of genetic effects.

true.

However an increase in the number of individuals receiving radiation exposure will increase likelihood that two individuals having the same type of mutation will have offspring. t/f

true. Damage from recessive mutations may sometime manifest itself more subtly and may appear as disorders related to metabolism or the immune system..

Although studies from Hiroshima and Nagasaki confirm that high doses of ionizing radiation cause cancer, radiation is not a highly effective cancer-causing agent. (t/f)

true. Follow-up studies of approximately 82,000 atomic bomb survivors from 1950 to 1987, Reveal an excess of only 250 cancer deaths attributed to radiation exposure; instead of the expected 4500 cancer deaths, 4750 actually occurred, Means that of about every 300 atomic bomb survivors, 1 died of a malignancy attributed to an average whole-body radiation dose of approximately 0.14 Sv

Although the risk of radiation induced leukemia is greater when embryo-fetus is irradiated during first trimester leukemia may also be induced during 2nd and 3rd trimesters. (t/f)

true. Studies of children irradiated during the 2nd and 3rd trimesters have not demonstrated significant rates of cancer and leukemia effects.

, the chance of radiation-induced cataracts occurring as a result of any diagnostic imaging procedure is very remote.

true. pts can also be offered eye shield

Skeletal damage from exposure to radiation most frequently occurs during the period from week

week 3 to week 20