Ch 7-9 Flashcards
Branch of biology concerned with the effects of ionizing radiation on living systems
Radiation biology
3 areas of study included in radiation biology
Sequence of events occurring after the absorption of energy from ionizing radiation Action of the living system to make up for the consequences of this energy assimilation Injury to the living system that may be produced
Damages living systems by ionizing the atoms comprising the molecular structure of these systems
Ionizing radiation
Biologic damage begins with the ionization produced by various types of radiation such as (5)
X-rays Gamma rays Alpha particles Beta particles Protons
________ will not bond properly in molecules
Ionized atoms
3 things that vary among the different types of radiation and determine the extent to which different radiation modalities transfer energy (harm/damage) into biologic tissue
Charge Mass Energy
3 important concepts that help us understand the way ionizing radiation causes injury and how the effects may vary in biologic tissue
Linear energy transfer Relative biologic effectiveness Oxygen enhancement ratio
The average energy deposited per unit length of track by ionizing radiation as it passes through and interacts with a medium along its path A very important factor in assessing potential tissue and organ damage from exposure to ionizing radiation
Linear Energy Transfer (LET)
What is the unit of LET?
keV/μm
2 radiation categories according to LET
Low-linear energy transfer radiation High-linear energy transfer radiation (more damage)
What is the rate of energy from ionizing radiation used for diagnostic purposes to soft biologic tissue?
About 3 keV/μm
When low-LET radiation interacts with tissue it causes damage to a cell primarily through an _______ action that involves the production of molecules called __________ (bad for you)
Indirect, free radicals
2 examples of low LET radiation
X-rays Gamma rays
6 examples of high LET radiation
Alpha particles Beta particles Protons Ions of heavy nuclei Charged particles released from interactions between neutrons and atoms Low-energy neutrons
High LET = _______ RBE
High
Because low-LET radiation generally causes sublethal damage to DNA, ______________ can usually reverse the damage
Repair enzymes
The LET for alpha particles is ______ times the LET of electrons
1000
High LET radiation is of greatest concern when _______________ is possible
Internal contamination
4 examples of internal contamination, that is when a radionuclide has been:
Implanted Ingested Injected Inhaled
Describes the relative capabilities of radiation with differing LETs to produce a particular biologic reaction
Relative biologic effectiveness (RBE)
The ratio of the radiation dose required to cause a particular biologic response of cells or organisms in any oxygen-deprived environment to the radiation dose required to cause an identical response under normal oxygenated conditions
Oxygen enhancement ratio (OER)
What is the OER of x-rays and gamma rays when the radiation dose is high?
3.0
What is the OER of x-rays and gamma rays when the radiation dose is below 2 Gyt?
2.0
Oxygenated state
Aerobic
Low oxygen
Anoxic
When irradiated in an aerobic state, biologic tissue is more sensitive to radiation than when it’s exposed to radiation under anoxic conditions
Oxygen effect
Without oxygen, damage produced by the indirect action on a biologic molecule may be repaired, but when damage occurs through an oxygen-mediated process, the end result is permanent/fixed
Oxygen fixation hypothesis
In living systems, biologic damage resulting from exposure to ionizing radiation may be observed on 3 levels
Molecular Cellular Organic
Any visible radiation-induced injuries of living systems at the cellular or organic level always begin with damage at this level Results in the formation of structurally changed molecules that may impair cellular functioning
Molecular level
If radiation damages the germ cells, the damage may be passed on to future generations in this form
Genetic mutations
2 classifications of ionizing radiation interaction on a cell
Direct action (e.g., in DNA) Indirect action (e.g., in H2O)
Biologic damage occurs as a result of ionization of atoms on essential molecules that may potentially cause these molecules to become inactive or functionally altered
Direct action
The effects produced by free radicals that are created by the interaction of radiation with water molecules Essentially all effects of irradiation in living cells result from this action
Indirect action
Why do essentially all effects of irradiation in living cells result from indirect action?
Because the human body is composed of 80-85% water and less than 1% DNA
Ionization of water molecules Production of free radicals, undesirable chemical reactions and biologic damage, and cell-damaging substances Organic free radical formation The final result of the interaction of radiation with water is the formation of an ion pair (H+ and OH–) and two free radicals (H* and OH*)
Radiolysis
Ionizing radiation interacts with DNA macromolecule, transfers energy, and ruptures one of the molecule’s chemical bonds possibly severing one of the sugar-phosphate chain side rails Repair enzymes are often capable of reversing this damage
Single-strand break Point mutation
Further exposure of the affected DNA macromolecule to ionizing radiation can lead to additional breaks in the sugar-phosphate molecular chain(s) Breaks may also be repaired but are not repaired as easily as single-strand breaks If repair does not take place, further separation may occur in the DNA chains, threatening the life of the cell
Double-strand break
Double-strand breaks occur more commonly with densely ionizing (_____-LET) radiation
High
3 effects of ionizing radiation on DNA
Single-strand break Double-strand break Mutation
In general, interaction of high-energy radiation (high-LET) with a DNA molecule causes either a loss of or change in a nitrogenous base on the DNA chain (double-strand) Direct consequence of this damage is an alteration of the base sequence May not be reversible and may cause acute consequences for the cell If cell remains viable, incorrect genetic information will be transferred to one of the two daughter cells when the cell divides to future generations
Mutation
The concept of radiation damage resulting from discrete and random events; may be used to explain cell death and nonfatal cell abnormalities caused by exposure to radiation
Target theory
Molecule that maintains normal cell function that is believed to be present in every cell and is vital to the survival of the cell
Master/key molecule
What is the master/key molecule presumed to be?
DNA
Ionizing radiation can adversely affect the cell; damage to the cell’s nucleus reveals itself in one of the following 7 ways
Instant death Reproductive death Apoptosis, or programmed cell death (interphase death) Mitotic, or genetic, death Mitotic delay Interference with function Chromosome breakage
The human body is composed of different types of cells and tissues, which _____ in their degree of radiosensitivity
Vary
4 examples of radiosensitive cells
Basal cells of the skin Blood cells such as lymphocytes (white blood cells) and erythrocytes (red blood cells) Intestinal crypt cells Reproductive germ cells
3 examples of radioinsensitive cells
Brain cells Muscle cells Nerve cells
As LET increases, the ability of the radiation to cause biologic effects also generally ________ until it reaches a maximal value
Increases
Oxygen enhances the effects of ionizing radiation on biologic tissue by _________ tissue radiosensitivity
Increasing
The radiosensitivity of cells is directly proportional to their reproductive activity and inversely proportional to their degree of differentiation True for all types of cells in the human body The most pronounced radiation effects occur in cells having the least maturity and specialization or differentiation, the greatest reproductive activity, and the longest mitotic phases
Law of Bergoiné and Tribondeau
Equal doses of ionizing radiation produce ________ degrees of damage in different kinds of human cells because of differences in cell radiosensitivity
Different
The more mature and specialized in performing functions a cell is, the ________ sensitive it is to radiation
Less
Ionizing radiation adversely affects blood cells by depressing the number of cells in the peripheral circulation; therefore, the use of blood tests for purposes of dosimetry is not valid
Hematologic depression
A whole-body dose of what delivered within a few days produces a measurable hematologic depression?
0.25 Gyt
The higher is the radiation dose received by the bone marrow, the _______ is the severity of the resulting cell depletion
Greater
Precursors of red blood cells are among the most sensitive of human tissues; mature red blood cells are much less radiosensitive
Erythrocytes
Depletion of red cells is not usually the cause of death in high-dose irradiation; what is?
Infection
Signifies the whole body dose of radiation that can be lethal to 50% of the exposed population within 30 days Quantitative measurement that is fairly precise when applied to experimental animals LD 50 for humans may require more than 30 days for its full expression
LD 50/30
What is the lethal dose of human beings usually given as and why?
LD 50/60 because a human’s recovery is slower than that of laboratory animals, and death may still occur at a later time following a substantial whole-body exposure
What is the estimated lethal whole-body dose for humans?
3.0-4.0 Gyt
What is the most radiosensitive blood cells in the human body?
Lymphocytes
Another kind of white blood cell that play an important role in fighting infection, a decrease in the number of these cells brought on by radiation exposure also increases a person’s susceptibility to infection (ex: radiation therapy)
Neutrophils
What radiation dose is sufficient to noticeably depress the number of lymphocytes present in the circulating blood?
A dose as low as 0.25 Gyt
What is the normal white blood cell count for an adult?
Ranges from 5,000-10,000/mm^3 of blood
At the dose level of what does complete blood cell recovery occur shortly after irradiation?
0.25 Gyt or less
When a higher dose range of whole body radiation of what is received, the lymphocyte count decreases to zero within a few days (full recovery generally requires a period of several months after this level of exposure)?
0.5-1 Gyt
Scavenger type of white blood cells that fight bacteria; if they’re affected by radiation, they can’t fight bacteria
Granulocytes
Initiate blood clotting and prevent hemorrhage If affected by radiation, your blood won’t clot so you won’t stop bleeding if you cut yourself
Thrombocytes/platelets
2 prime candidates for chromosome aberrations in circulating lymphocytes
Patients for whom high-level fluoroscopy was employed Patients for whom very long fluoroscopic exposure times occurred (ex: cardiac catheterization and other specialized invasive procedures)
Biologic effects of radiation that occur relatively soon after humans receive high doses of ionizing radiation Substantial evidence of the consequences of such effects comes from numerous laboratory animal studies and data from observation of some irradiated human populations Not common in diagnostic imaging Produced by a substantial dose of ionizing radiation
Early effects
Ionizing radiation produces the greatest amount of biologic damage in the human body when a large dose of densely ionizing (_______-LET) radiation is delivered to a large or radiosensitive area of the body
High
4 somatic and genetic (hereditary) damage factors
The quantity of ionizing radiation to which the subject is exposed The ability of ionizing radiation to cause ionization of human tissue The amount of body area exposed The specific body parts exposed
Biologic damage sustained by living organisms (such as humans) as a consequence of exposure to ionizing radiation
Somatic effects
2 classifications of somatic effects depending upon the length of time from the moment of irradiation to the first appearance of symptoms of radiation damage
Early somatic effects Late somatic effects
Effects are directly related to the dose received; as the radiation dose increases, the severity of these effects also increases. These results have a threshold, a point at which they begin to appear and below which they are absent The amount of biologic damage depends on the actual absorbed dose of ionizing radiation Consequences include cell killing
Deterministic somatic effects (formerly called nonstochastic somatic effects)
2 categories of late effects (both of these types of late radiation-induced changes are consequences of high-level radiation exposure or of low doses of radiation delivered over a long interval of time)
Late deterministic somatic effects Late stochastic (probabilistic) effects
Depend on the time of exposure to ionizing radiation Requires a substantial dose of ionizing radiation to produce these biologic changes soon after irradiation With the exception of certain lengthy high-dose-rate procedures, diagnostic imaging examinations do not usually impose radiation doses sufficient to cause early deterministic effects High-dose effects include nausea, fatigue, erythema, epilation, blood disorders, intestinal disorders, fever, dry and moist desquamation, depressed sperm count in the male, temporary or permanent sterility in the male and female, and injury to the central nervous system (at extremely high radiation doses)
Early deterministic somatic effects
4 times early deterministic somatic effects appear within the time of radiation exposure
Minutes Hours Days Weeks
A whole-body dose of what can result in many of the manifestations or organic damage occurring in succession (acute radiation syndrome- early deterministic somatic effects)?
6 Gyt
Radiation sickness occurring in humans after whole-body reception of large doses of ionizing radiation delivered over a short period of time A collection of symptoms associated with high-level radiation exposure
Acute radiation syndrome (ARS)
Data from epidemiologic studies of human populations exposed to doses of ionizing radiation sufficient to cause ARS have been obtained from (4)
Atomic bomb survivors of Hiroshima and Nagasaki Marshall Islanders who were inadvertently subjected to high levels of fallout during an atomic bomb test in 1954 Nuclear radiation accident victims such as those injured in the 1986 Chernobyl disaster Patients who have undergone radiation therapy
3 separate dose-related syndromes occur as part of the total-body syndrome (ARS)
Hematopoietic syndrome (bone marrow syndrome) Gastrointestinal syndrome Cerebrovascular syndrome
Hematopoietic syndrome (bone marrow syndrome) occurs when people receive whole-body doses of ionizing radiation in what range that decreases the number of bone marrow stem cells?
1-10 Gyt
Radiation exposure causes the number of red blood cells, white blood cells, and platelets in the circulating blood to decrease When the cells of the lymphatic system are damaged, the body loses some of its ability to combat infection Because additional bone marrow cells are destroyed, as the radiation dose escalates, the body becomes more susceptible to infections (mostly from its own intestinal bacteria) and more prone to hemorrhage; when death occurs, it’s a consequence of bone marrow destruction
Hematopoietic syndrome (bone marrow syndrome)
Death may occur 6-8 weeks after irradiation in some sensitive human subjects who receive a whole-body dose exceeding what (hematopoietic syndrome [bone marrow syndrome])?
2 Gyt
If the radiation exposure isn’t lethal (1-2 Gyt, < 2 Gyt) bone marrow cells will eventually repopulate; many of these people recover how long after irradiation and the actual dose of radiation received and the irradiated person’s general state of health at the time of irradiation determine the possibility of recovery?
3 weeks-6 months
Gastrointestinal syndrome appears at a threshold dose of approximately what and peaks after a dose of what?
6 Gyt, 10 Gyt
Without medical support to sustain life, exposed persons receiving doses of what may die 3-10 days after being exposed (gastrointestinal syndrome)?
6-10 Gyt
Survival time doesn’t change with dose A few hours after the dose severe nausea, vomiting, and diarrhea persist for as long as 24 hours followed by a latent period as long as 5 days (during this time, the symptoms disappear); the manifest illness stage follows the period of false calm and the human subject experiences: severe nausea, vomiting, diarrhea and other signs and symptoms that may occur include: fever (as in hematopoietic syndrome), fatigue, loss of appetite, lethargy, anemia, leukopenia (decrease in the number of white blood cells), hemorrhage (GI tract bleeding occurs because the body loses its blood-clotting ability), infection, electrolyte imbalance, emaciation Examples of humans who died as a result: workers and firefighters at Chernobyl
Gastrointestinal syndrome
What is the most radiosensitive part of the GI tract and why?
Small intestine because there’s a lot of absorption and cell regeneration
What is the most radiosensitive part of the GI tract and why?
Small intestine because there’s a lot of absorption and cell regeneration
Cerebrovascular syndrome results when the central nervous system cardiovascular system receive doses of what (a dose of this magnitude can cause death a few hours to 2-3 days after exposure after exposure)?
50 Gyt
Eight signs and symptoms: excessive nervousness, confusion, severe nausea, vomiting, diarrhea, loss of vision, burning sensation of the skin, loss of consciousness A latent period lasting up to 12 hours follows and during this time, symptoms lessen or disappear After the latent period, the manifest illness stage occurs and during this period, the prodromal syndrome recurs with increased severity, and other symptoms appear, including: disorientation and shock, periods of agitation alternation with stupor, ataxia (confusion and lack of muscular coordination), edema in the cranial vault, loss of equilibrium, fatigue, lethargy, convulsive seizures, electrolytic imbalance, meningitis, prostration, respiratory distress, vasculitis, coma Damaged blood vessels and permeable capillaries permit fluid to leak into the brain and cause an increase in fluid content Final result of this damage is failure of the CNS and cardiovascular systems, which causes death withinn a matter of minutes Because the GI and hematopoietic systems are more radiosensitive than the CNS, they’re also severely damaged and fail to function after a dose of this magnitude (hematopoietic and GI syndrome also going on)
Cerebrovascular syndrome
4 major response stages of ARS
Prodromal, or initial, stage Latent period Manifest illness Recovery or death
Stage of ARS that occurs within hours after a whole-body absorbed dose of 1 Gyt or more Characterized by nausea and vomiting Severity of these symptoms is dose related: the higher the dose, the more severe the symptoms
Prodromal, or initial, stage
Stage of ARS about 1 week during which no visible symptoms occur
Latent period
Stage toward the end of the 1st week of ARS The period when signs and symptoms that affect the hematopoietic, GI, and cerebrovascular systems become visible
Manifest illness
In severe high-dose cases, emaciated human beings eventually die If, after a whole-body sublethal dose such as 2-3 Gyt, exposed persons pass thru the first three stages of ARS but show less severe symptoms than those seen after superlethal doses of 6-10 Gyt, this may occur in about 3 months
Recovery or death
Whole-body doses greater than what may cause the death of the entire pop in 30 days without medical support?
6 Gyt
In the repair of sublethal damage, oxygenated cells, which receive more nutrients, have a _______ prospect for recovery than do hypoxic cells that consequently receive fewer nutrients
Better
Repeated radiation injuries have a _________ effect
Cumulative
Approximately what percent of radiation damage is irreparable, whereas the remaining what percentage may be repaired over time?
10%, 90%
A destructive response in biologic tissue can occur when any part of the human body receives a high radiation dose Significant cell death usually results after such a substantial partial-body exposure leading to atrophy of organs and tissues Consequence: organs and tissues sustaining such damage may lose their ability to function and die, or they may recover If recovery occurs, it may be partial or complete, depending on the type of cells involved and the dose of radiation received If organ and tissue recovery fails to occur, necrosis of the irradiated biologic structure results
Local tissue damage
Shrinkage of organs and tissues
Atrophy
3 things organ and tissue response to radiation exposure depends on
Radiosensitivity Reproductive characteristics Growth rate
3 layers of the skin
Epidermis Dermi Hypodermis
Outer layer of the skin
Epidermis
Middle layer of the skin
Dermis
Subcutaneous layer of the skin
Hypodermis
4 accessory structures of the skin
Hair follicles Sensory receptors Sebaceous glands Sweat glands
Significant reddening of the skin caused by excessive exposure to ionizing radiation that lead to cancerous lesions (historical evidence)
Radiodermatitis
Shedding of the outer layer of the skin (dry or moist/oozing) occurs at higher radiation doses (historical evidence)
Desquamation
Moderate doses of radiation may result in temporary hair loss Large doses of radiation may result in permanent hair loss
Epilation or loss of hair (alopecia)
X-rays in the energy range of 10-20 kVp Historical evidence of treating skin diseases such as ringworm
Grenz rays
Oncology patients receiving x-rays in the range of 200-300 kVp have demonstrated significant evidence of skin damage (oncology patients who underwent such treatments in earlier years for deep-seated tumors)
Orthovoltage radiation therapy treatment
3 effects of ionizing radiation on the skin
Radiodermatitis Desquamation Epilation or loss of hair (alopecia)
4 phases in the development of male germ cells
Spermatogonia Spermatocyte Spermatid Sperm
4 phases in the development of female germ cells
Primordial follicle Mature follicle Corpus iuteum Ovum
Doses as low as what can depress the male sperm population and has the potential to cause genetic mutations in future gens; in girls and women, a gonadal dose of what may delay or suppress menstruation?
0.1 Gyt
Temporary sterility may occur and last for as long as 12 months when the testes receive a radiation dose of what?
2 Gyt
Permanent sterility of the testes is most likely to be induced by a radiation dose of what?
5 or 6 Gyt
A single radiation exposure of what to the ovaries usually results in temporary sterility of the woman, whereas a dose of what results in permanent sterility?
2 Gyt 5-6 Gyt
Whole-body dose of ionizing radiation as low as what produce a measurable hematologic depression?
0.25 Gyt
3 things the hematopoietic system consists of
Bone marrow Circulating blood Lymphoid organs
3 lymphoid organs
Lymph nodes Spleen Thymus gland
Study of cell genetics with emphasis on cell chromosomes
Cytogenetics
A cytogenetic analysis of chromosomes may be accomplished through the use of a chromosome map consisting of a photomicrograph
Karyotype
Photograph that is taken of the human cell nucleus during metaphase, when each chromosome can be individually demonstrated
Photomicrograph
The phase of cell division in which chromosome damage caused by radiation exposure can be evaluated Chromosome aberrations (deviation from normal development or growth) and chromatid aberrations have been observed at this phase
Metaphase
Radiation-induced damage at the cellular level may lead to measurable somatic and genetic damage in the living organism as a whole later in life; these outcomes are the long-term results of radiation exposure
Late effects
3 examples of measurable late biologic damage
Cataracts Leukemia Genetic mutations
A science that deals with the incidence, distribution, and control of disease in a population Studies consist of observations and statistical analysis of data, such as the incidence of disease within groups of people
Epidemiology
Epidemiology studies include the risk of radiation-induced cancer The incident rates at which these irradiation-related malignancies occur are determined by comparing the natural incidence of cancer occurring in a human population with the incidence of cancer occurring in an __________ population Risk factors are then determined for the general human population Historical evidence of radiation-induced cancer in early radiation workers and irradiated populations Epidemiologic studies are of significant value to scientists who use the information from these studies to formulate dose-response estimates to predict the risk of cancer in human populations exposed to low doses of ionizing radiation
Irradiated
Radiobiologists engaged in research have a common goal to establish relationships between radiation and dose-response 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 Radiation dose-response relationship is demonstrated graphically through a curve that maps the observed effects of radiation exposure in relation to the dose of radiation received As radiation dose escalates, so do most effects How much radiation received to give you this response
Dose-response curves
Dose received on dose-response curves
Horizontal axis
Biologic effects observed on dose-response curves
Vertical axis
Straight line
Linear
Curved to some degree
Nonlinear
A point at which a response or reaction to an increasing stimulation first occurs With reference to ionizing radiation, below a certain radiation level or dose, no biologic effects are observed Biologic effects begin to occur only when this level or dose is reached
Threshold
Any radiation dose has the capability of producing a biologic effect If ionizing radiation functions as the stimulus, and the biologic effect it produces is the response, and if a this relationship exists between radiation dose and a biologic response, some biologic effects will be caused in living organisms by even the smallest dose of ionizing radiation No radiation dose can be considered absolutely safe
Nonthreshold
Most stochastic effects (e.g., cancer) and genetic (hereditary) effects at low dose levels from low-LET radiation, such as the type of energy used in diagnostic radiology, appear to follow this curve Leukemia, breast cancer, and heritable damage are presumed to follow this curve
Linear-quadratic nonthreshold curve (LQNT)
The equation that best fits the data has components that depend on dose to the first power (linear or straightline behavior) and also dose squared (quadratic/curved behavior)
Linear-quadratic
The chance of a biologic response to ionizing radiation is directly proportional to the dose received Recommends curve of radiation dose-response for most types of cancer
Linear nonthreshold (LNT) curve
Deterministic effects of significant radiation exposure such as skin erythema and hematologic depression may be demonstrated graphically 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
Linear threshold dose-response curve
When living organisms that have been exposed to radiation sustain biologic damage
Somatic (i.e., body) effects
2 classifications of somatic effects
Stochastic effects Deterministic effects
The probability that the effect happens depends upon the received dose, but the severity of the effect does not Example: occurrence of cancer
Stochastic effects
Both the probability and the severity of the effect depend upon the dose Example: a cataract
Deterministic effects
6 late deterministic somatic effects
Cataract formation Fibrosis Organ atrophy Loss of parenchymal cells Reduced fertility Sterility
Effects of radiation on the embryo-fetus in utero that depend on the fetal stage of development and the radiation dose received
Teratogenic effects
8 teratogenic effects
Embryonic, fetal, or neonatal death Congenital malformations Decreased birth weight Disturbances in growth and/or development Increased stillbirths Infant mortality Childhood malignancy Childhood mortality
2 late stochastic effects
Cancer Genetic (heritable) effects
Consequences of radiation exposure that appear months or years after such exposure
Late somatic effects
3 things late somatic effects may result from
Previous whole- or partial-body acute exposure Previous high radiation doses Long-term low-level doses sustained over several years
Late effects that can be directly related to the dose received; slow developing changes to the body from radiation exposure Not likely to occur from diagnostic imaging procedures
Late deterministic somatic effects
Late responses in the body to radiation exposure that do not have a threshold occur in an arbitrary or probabilistic manner and have a severity that does not depend on dose Could be initiated by even the smallest amount of radiation exposure if many low probability occurrences were to be simultaneously realized.
Late stochastic effects
No conclusive proof exists that low-level ionizing radiation exposure below what causes a significant increase in the risk of malignancy?
0.1 Sievert (Sv)
3 categories of adverse health consequences require study at low-levels of exposure
Cancer induction Damage to the unborn from irradiation in utero Genetic (hereditary) effects
Cells that survive the initial irradiation and then retain some form of damage that persists and is passed on to future generations of the cell of that event are responsible for producing late effects
“Memory”
3 major types of late effects
Carcinogenesis (stochastic event) Cataractogenesis (deterministic event) Embryologic effects (birth defects) (stochastic events)
At low doses, below what, which includes groups such as occupationally exposed individuals and virtually all patients in diagnostic radiology, the risk of cancer is not directly measurable in population studies?
0.1 Sv
2 reasons the risk of cancer is not directly measurable in population studies
The risk is overshadowed by other causes of cancer in humans The risk is zero
2 current radiation protection philosophies
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)
They 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 __________ the minimal theoretical risk to the patient for developing cancer as a stochastic late response to radiation exposure
Exceeds
2 models used by researchers for extrapolation of risk from high-dose to low-dose data
Linear Linear-quadratic (leukemia only)
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
Cancer
Radiation induced cancer may take how long to develop in humans?
5 or more years
The physical appearance of cancer induced by ionizing radiation does not appear _________ than a cancer caused by other agents
Different
Cancer caused by ______-level radiation is difficult to identify
Low
4 types of solid tumors occurrening in survivors of Hiroshima and Nagasaki
Thyroid Breast Lung Bone cancers
In general, Japanese women have a _______ incidence of breast cancer than U.S. and Canadian women.
Lower
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 _______ with radiation dose
Rises
Follow-up studies of approximately 82,000 atomic bomb survivors reveal an excess of only how many 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
250 cancer deaths
There is a high probability that a single dose of approximately what will induce the formation of cataracts?
2 Gy
What do cataracts result in?
Partial or complete loss of vision
Radiation-induced cataracts in humans follow a what kind of relationship?
Threshold, nonlinear dose-response
3 stages of gestation in humans
Preimplantation Organogenesis Fetal stage
Most radiosensitive stage of gestation in humans
Organogenesis First trimester
Biologic effects of ionizing radiation on future generations
Genetic (hereditary) effects
3 causes of genetic (hereditary) mutations
Radiation-induced damage to the DNA molecule in the sperm or ova of an adult Natural spontaneous mutations Resultant genetic disorders or diseases
