Week 9 - Stochastic Effects & Late Tissue Reactions Flashcards
What are late effects?
Consequences of radiation exposure that appear months or years after the exposure.
What are the two types of late tissue effects?
Stochastic or Tissue reactions
What are Stochastic effects also known as?
Probabilistic effects
What are stochastic effects?
Mutational or randomly occurring biologic changes that occur months or years after high level and possibly low level of radiation exposure
What are examples of Stochastic effects?
Cancer and genetic effects
What is the relationship between stochastic effects and disease incidence?
Directly proportional - disease incidence increases proportionally with dose
What is relationship between severity of disease and dose?
They’re independent of each other - severity is not dose dependent
What is the threshold of Effects?
No threshold
What are examples of late biologic damage?
- Cataracts (late tissue reaction)
- Leukemia (stochastic)
- Genetic mutations (stochastic)
What is epidemiology?
A science that deals with the incidence, distribution and control of disease in a population
What do epidemiological studies consist of?
Observations and statistical analysis of data, such as the incidence of disease within groups of people
What studies are included in epidemiologic studies?
The risk of radiation- induced cancer
What are the incident rates at which irradiation related malignancies occur determined by?
Comparing the natural incidence of cancer occurring in a human population with the incidence of cancer occurring in an irradiated population
What are determined from the epidemiologic studies?
Risk factors for the general human population
What is the significance of epidemiologic studies to radiobiologists?
They use the information from the studies to formulate dose-response estimates to predict the risk of cancer in human populations
What is another term for Carcinogenesis?
Tumorigenesis
What is carcinogenesis?
The formation of cancer
What is the most significant late stochastic effect?
Cancer
What is the occurrence of cancer and the threshold?
Random occurrence that does not have a threshold
Is the severity of cancer dose related?
No
How is a radiation dose-response relationship demonstrated?
Graphically through a curve
What does a radiation dose-response graph map?
The observed effects of radiation exposure in relation to the dose of radiation received
What is represented on the horizontal axis of the graph?
Dose received
What is represented by the vertical axis of the graph?
Biological effects observed
What is a general rule of the DR relationship?
As radiation dose escalated so do most effects
What are the DR relationship graphs used for?
To predict the risk of occurrence of malignancies in human populations that have been exposed to low levels of ionizing radiation
How are the observed effects of radiation demonstrated?
By the incidence of a disease or the severity of an effect
What are the two types of DR curves?
Linear and non-linear
What are the two types of threshold records in a DR curve?
Threshold or non-threshold
What is a Sigmoid DR curve?
An S shaped curve (non-linear)
What are Sigmoid curves generally used for?
In radiation therapy to demonstrate high-dose cellular response
What is a threshold?
A point at which a response or reaction to an increasing stimulation first occurs
How does threshold apply to radiation?
It means that below a certain radiation level or dose, no biological effects are observed
When would biological effects begin with a threshold relationship?
Only when the threshold or dose level is reached
What is non-threshold as it pertains to radiation?
Indicates that the radiation absorbed dose of any magnitude has the capability of producing biological effects
For the linear non-threshold curve, what is the relationship between dose and biological effects?
Directly proportional, the severity of biological effects increase directly with the magnitude of absorbed dose
What is a general rule of nonthreshold doses?
That no radiation dose can be considered absolutely safe
What is BEIR?
Committee on the Biological Effects of Ionizing Radiation
What did the BEIR committee concluded in 1980?
That most stochastic and hereditary effects at low dose levels from low-LET radiation, follow a linear-quadratic non-threshold dose response curve
What did BEIR do in 1990?
Revised risk estimates to conclude that the risk of radiation exposure was about 3-4 times greater than previously projected
What type of DR curve does the BEIR committee recommend for most types of cancer?
Linear non-threshold curve
What does the LNT curve imply?
That the biological response to ionizing radiation is directly proportional to the dose received
What must radiographers never fail to employ with diagnostic imaging?
Aggressive radiation safety measures since it follows an LNT curve and all radiation exposure levels possess the potential to cause biological damage
What does the BEIR committee believe the LQNT model is more accurate to reflect?
The stochastic and genetic effects at low-dose levels from low-LET radiation
What effects are presumed to follow the LQNT curve?
Leukemia, breast cancer and heritable damage
What acute reactions to radiation exposure are demonstrated through a linear threshold dose-response curve?
Skin erythema and hematological depressions
Why are Sigmoid curves best used for radiation therapy?
They demonstrate high-dose cellular responses to radiation absorbed within specific locations, such as skin, lens of the eye and blood cells
What does the curve indicate for different effects?
Different effects require different minimal doses
What happens at the tail of the sigmoid curve?
Indicates that limited recovery occurs at lower doses
For the highest radiation doses what happens to the curve?
The curve gradually levels off and then veers downward because the specimen or tissue dies before observable effects appear
What does continued use of the linear dose-response model have the potential to do?
Exaggerate the seriousness of radiation effects at lower dose levels from low-LET radiation
What id the linear dose response model accurate in representing?
The effects of high-LET radiation at higher doses
What approach have regulatory agencies adopted when assessing risk?
Use a conservative approach that may overestimate risk but will not underestimate it
What are somatic effects?
When living organisms that have been exposed to radiation sustain biological damage
What are the two classifications of somatic effects?
Stochastic and tissue reactions
What are is a general rule of stochastic effects?
The probability that the effect happens depends on the dose received, but the severity of the effect is not based on dose
What is an example of stochastic effect?
Occurrence of cancer
What is a general rule for tissue reactions?
Both the probability and the severity of the effect depend upon dose
What is an example of tissue reactions?
Cataracts
What are the full list of Late Tissue reactions?
- Cataract formation
- Fibrosis
- Organ atrophy
- Loss of parenchyma cells
- Reduced fertility
- Sterility
What are Teratogenic effects?
Effects of radiation on the embryo-fetus in utero that depend on the fetal stage of development and radiation dose received
What are types of Teratogenic effects?
- Embryonic, fetal or neonatal death
- Congenital malformations
- Decreased Birth weight
- Disturbances in growth/development
- Increased stillbirths
- Infant mortality
- Childhood malignancy
- Childhood mortality
What are the two types of stochastic effects?
Cancer and Genetic effects
What are late somatic effects?
Consequences of radiation exposure that appear months or years after exposure
What do late somatic effects result from?
- previous whole or partial body acute exposure
- previous high radiation doses
- long term low level doses sustained over several years
Why are risk estimates for humans contracting cancer from low level radiation controversial?
There is no conclusive proof that low level IR exposure below 0.1 Gy cause any significant increase in risk of cancer
What are the 3 categories of adverse health consequences that the medical community believes require studies on at low-level?
- cancer induction
- damage to the unborn from irradiation in utero
- genetic effects
What does cells that survive initial irradiation possess?
They retain a “memory” of the event which are responsible for producing late effects
In theory, what cells or organs could produce stochastic effects?
Damage to one or a few cells can produce stochastic effects
What is the relationship between tissues reactions and late onset?
Typically tissue reactions do not usually demonstrate a late onset
What are the 3 major types of late effects?
- carcinogenesis
- cataractogenesis
- embryologist effects
Which type of radiation dose can risk be measure for in human populations?
High doses of
Why are low dose risk non directly measurable?
The risk is overshadowed by other causes of cancers in humans or the risk could be 0
How are risk estimates for cancer determined for low-doses?
High dose data is extrapolated, where risk has been directly observed, and just applied to low-doses
What are terms are risk models usually given in?
Absolute risk or Relative risk
What do both risk 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
What does the absolute risk model forecast?
Forecasts that a specific number of malignancies will occur as a result of exposure
What does the relative risk model forecast?
That the number of excess cancers will increase as the natural incidence of cancer increases with the advancing age of the population
What have epidemiological studies for determining risk of cancer for diagnostic radiology?
That the benefit to that patient of the information gained from imaging greatly exceeds the minimal theoretical risk
What type of effect does 1989 BEIR V report the LQNT model be used for?
Leukemia
What model does BEIR Committee recommend Linear model be used for?
All other cancers
How does the linear model apply to the occurrence of cancer from high and low doses?
Accurately assesses the risk for high dose information but exaggerates risk for low doses
How does the linear quadratic model apply to the occurrence of cancer from high and low doses?
The model satisfactorily assesses risk from high doses but underestimates the risk for low doses
What has been used to prove ionizing radiation induces cancer?
Lab experiments with animals and statistical studies of human populations
How long can it take for cancer to appear in humans?
May take 5 or more years
How does the physical appearance of cancer from ionizing radiation compare to cancer from different agents?
They don’t appear different at all
What human evidence exists for radiation carcinogenesis?
- Radium watch dial painters from the 1920s
- Uranium miners from 1950s
- Early medical radiation workers
- Atomic bomb survivors
- Patients with benign postpartum mastitis who were given radiation therapy
- Evacuees from Chernobyl
How has the incidence of leukemia changed over the years?
It has slowly declined since the late 1940s
How has the incidence of other radiation-induced malignancies changed over the years? The
They have continued to escalate since the 1950s
What types of cancers has there been an increase in since the 50s?
Solid tumors such as thyroid, breast and bone cancer
In general what is the rate of natural incidence of breast cancer in Japanese women?
Much lower than incidence in women from the US or Canada
What have studies of Japanese atomic bomb survivors proven in regards to breast cancer?
That ionizing radiation can induce breast cancer and incidence of breast cancer in these women has risen with radiation dose
What is the relative risk for breast cancer for female atomic bomb survivors?
Ranges form 4:1 up to 10:1
What have studies from Japan identified regarding ionizing radiation as a cancer causing agent?
That high doses of IR cause cancer, but radiation isn’t a highly effective cancer causing agent
What was revealed in follow-up studies of bomb survivors from 1950-1987?
An excess of only 250 cancer deaths were attributed to radiation exposure, meaning that of 300 survivors only 1 died due to malignancies attribute to radiation exposure
What have more recent studies of the atomic bomb attacks revealed?
That more gamma radiation exposure and less neutron exposure caused radiation damage
What is the percent breakdown of neutron vs gamma radiation from the atomic bomb?
10% neutron and 90% gamma radiation
What radioactive material was spread as a result of the Chernobyl disaster?
Iodine-131 was spread and concentrates in the thyroid of those exposed
What is the most pronounced health effect of Chernoybl?
Thyroid cancer
What was administered to children in Poland and other countries to prevent thyroid cancer?
Potassium iodide
What is nonspecific lifespan shortening?
The reduction of lifespans as the result of ionizing radiation exposure
What effect does a single dose of 2 Gyt have on the eyes?
Induces the formation to cataracts
What is the result of cataractogenesis?
- partial or complete loss of vision
What type of radiation is effective in producing cataracts?
Highly ionizing neutron radiation
What type of DR curve do radiation induced cataracts follow?
Threshold non-linear dose response relationship
What are the 3 stages of gestation?
- Pre-implantation (0-9 days after conception)
- Organogenesis (10 days post conception - 12 weeks)
- Fetal stage (12 weeks to term)
What does the period of gestation dictate when it pertains to exposure?
It dictates the effects of ionizing radiation
What trimester is the most radiocensitive?
1st trimester because its when the embryo begins to divide
At which stage of gestation is the embryo most susceptible to congenital abnormalities?
The organogenesis stage
What happens to a embryo in the first two weeks of fertilization?
If the embryo is irradiated its certain death
What happens to embryo sensitivity as the pregnancy progresses?
It decreases as gestation progress
What were the embryonic effects from Chernobyl?
No apparent abnormalities were seen in babies born immediately after the explosion, but in the 5 years after higher effects were reported
What are genetic effects?
Biological effects of ionizing radiation on future generations
What are types of irradiation mutation?
- radiation-induced damage to the DNA molecule in the sperm or ova of an adult
- may manifest as various diseases or malformations
- may be transmitted to successive generations
What are spontaneous mutations?
Modifications of genetic material that occur naturally and without cause
What are examples of spontaneous mutations?
Hemophilia, Huntington’s disease, sickle cell anemia, cystic fibrosis and hydrocephalus
What are mutant genes incapable of?
Governing cells chemical reactions or controlling amino acid sequence
What is doubling dose?
The radiation dose that causes the # of mutations occurring in a given generation to increase to 2X their original occurance
