UNIT 3: Stochastic Effects & Late Tissue Reactions Flashcards
Late effects definition
The long-term results of radiation exposure. Late effects may be either stochastic or tissue reactions. Stochastic effects, such as the incidence of cancers in a population, typically are not noticeable for many years in the exposed population. Tissue reactions, such as skin effects, may be perceptible sooner in individuals, although months or years may pass before their full expression
Examples of late effects
Cataracts, Leukemia, Genetic mutations
Which late effects are considered random effects?
Leukemia and Genetic Mutations
What is cancer?
name used for a substantial group of diseases in which healthy cells have been transformed into nonstandard cells that divide uncontrollably. The process leads to an expansive growth of abnormal structures within various locations in the body and the destruction of surrounding body tissues such as bone marrow. (Also known as carcinogenesis/tumorigenesis)
How do we know radiation can cause cancer(list the human evidence)?
- Radium watch-dial painters (1920s and 1930s)
- Uranium miners (early years, and Navajo people of Arizona and New Mexico during the 1950s and 1960s)
- Early medical radiation workers (radiologists, dentists, technologists) (1896 to 1910)
- Japanese atomic bomb survivors (1945)
- Patients with benign postpartum mastitis who were given radiation therapy treatments (mid 1900s)
- Evacuees from the Chernobyl nuclear power station disaster in 1986
Label the dose response graph (curves)
- represents a linear (straight-line) nonthreshold curve of radiation dose–response relationship: indicates both that the response to radiation (in terms of biologic effects) is directly proportional to the dose of radiation and that no known level of radiation dose exists below which the chance of sustaining biologic damage is zero. stochastic effects like cancer
- represents a linear threshold curve of radiation dose–response relationship: indicates that a certain dose of radiation (threshold dose) must occur before a response will occur. early tissue reactions
- represents a nonlinear threshold curve of radiation dose–response relationship. generally employed in radiation therapy to demonstrate high-dose cellular response. late tissue reactions like cataracts
Stochastic effects vs Late tissue effects
-Stochastic: Typically are not noticeable for many years in the exposed population. The probability that the effect happens depends upon the received dose, but the severity of the effect does not. Usually cancer or genetic (hereditary) effects.
-Late tissue effects: Both the probability and the severity of the effect depend upon the dose. Examples: Cataract formation, sterility, reduced fertility, etc.
Absolute vs Relative Risk models
-Absolute: model estimates that a specific number of malignancies will occur as a result of exposure
-Relative: predicts that the number of excess cancers will increase as the natural incidence of cancer increases with advancing age in a population
What are the absolute and relative risk models used for?
To predict cancer risk
What are cataracts? What is the threshold dose that causes cataracts?
-Partial or complete loss of vision
-A single dose of approximately 2 Gyt will induce the formation of cataracts. NOW IT IS 0.5 Gyt.
-Radiation-induced cataracts in humans follow a threshold nonlinear dose-response relationship
What DRC(Dose Response Curve) is used for radiation induced cataracts?
Radiation-induced cataracts in humans follow a nonlinear threshold dose-response relationship
What are the effects to the embryo if irritated with a significant dose? (Stages and effects)
-Stages of gestation in humans: Preimplantation, Organogenesis, Fetal stages.
-Abnormalities include: Growth inhibition, Intellectual disability, Microcephaly, Genital deformities, Sensory organ damage
What is considered to be the most radiosensitive period of pregnancy?
First Trimester, during organogenesis, which occurs at approximately 10 days and lasts up to 12 weeks after conception
What are the effects of low-level ionizing radiation on the embryo-fetus?
The effects of low-level ionizing radiation on the embryo-fetus can only be poorly estimated. If the exposure occurs during a period of major organogenesis, the abnormality and its occurrence may be more pronounced.
What part do radiographers play in reducing exposures to pregnant patients?
radiation workers should exercise caution and employ appropriate safety measures when performing radiographic procedures on pregnant patients. For these procedures, if requested, medical physicists can make fetal dose estimates for specific patients based upon characteristics such as patient size and the actual technical parameters used in the studies in cases where there are concerns about medical management
What is a mutation?
the loss or change of a base in the DNA chain represents a mutation (Point mutations: genetic mutations at the molecular level)
Irradiation mutations
• 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
How does radiation cause mutations?
Ionizing radiation directly affects DNA structure by causing DNA breaks
Are radiation mutations thought to be dominant or recessive? Why?
-Radiation mutations can be either dominant or recessive, but Radiation is thought to cause primarily recessive mutations.
-For a recessive mutation to appear in the offspring, both parents must have the same genetic defect. This requires that the defect must be located on the same part of a specific DNA base sequence in each parent. Because this rarely occurs, the effects of recessive mutations are not likely to appear in a population. However, an increase in the number of individuals who receive radiation exposure raises the likelihood that two individuals with the same type of mutation will have children. Therefore, it is essential to limit the radiation exposure of the entire population.
What does doubling dose mean?
the amount of radiation required to double the rate of genetic diseases already occurring in the human population
List the doubling dose estimated for humans
The radiation doubling equivalent dose for humans, as determined from studies of the children of the atomic bomb survivors of Hiroshima and Nagasaki, is estimated to have a mean value of 1.56 Sv
Vocab: absolute risk
Model predicting that a specific number of excess cancers will occur as a result of exposure to ionizing radiation
Vocab: carcinogenesis
The production or origin of cancer
Vocab: cataractogenesis
The production or origin of cataracts
Vocab: linear non-threshold curve
An extrapolated (high dose values) graph which implies that the chance of a biologic response to ionizing radiation is directly proportional to the dose received no matter how low the dose is no radiation dose can be considered absolutely “safe.” Used for most types of cancers.
Vocab: Linear Quadratic non-threshold curve
A nonstraight line model used to calculate the occurrence of cancer by extrapolating from information associated with high levels of radiation to determine the risk associated with low doses
