Ch 34 Stochastic Effects Flashcards
What are Stochastic effects?
Late Effects
Stochastic effects follow a…
Linear, non-threshold dose response relationship
What are principle stochastic effects?
- Radiation induced malignancy
- Genetic effects
What type of effects are the result of low doses of radiation over a long period of time
Stochastic Effects
What are Local tissue Stochastic effects?
- Erythema (sunburning)
- Desquamation
- Late developing carcinoma
- Radiodermatitis
- Calluses
- Discoloration
- Tight, Brittle skin
What are local tissue effects of Chromosomes?
- Leukemia
- Chromosome damage to circulating lymphocytes
- Chromosome aberration that may not be apparent for years
What are cataracts?
Caused by high radiation to the lens of the eye
Test
Where do radiation induced cataracts occur?
Posterior pole of the lens
Who were the first people to have their lens affected by radiation?
Cyclotron physicists (1949)
By 1960 hundreds of cases of radiation induced ______ were reported.
Cataracts
Radiosensitivity of the eye is _____ ______
Age dependent
Radiation effect increases as…
Age increases
What is the latent period for radiation causing cataracts?
- 5-30 years
- Average is 15 years
Radiation induced cataracts follow a…
Non linear, threshold dose response relationship
During occupational exposure, are protective shields required for protection of the lens?
No, it is too low
What is the threshold dose before causing cataracts?
200 rad (2 Gy t)
At what dose do nearly 100% of irradiated subjects get cataracts?
Greater than 1,000 rad (Gy t)
At worst, humans can expect a reduced life span of ____ days for every rad (mGy t)
10
What causes radiation induced life span shortening?
Accelerated premature aging and death
What are some risky conditions that shorten life span?
- Being male (2,800)
- Heart disease (2,100)
- Smoker (1,600)
- Cancer (980)
- MVA (200)
- Occupational accidents (74)
- Rad worker (12)
What are the (3) ways to calculate risk?
- Relative
- Excess
- Absolute
What is Relative Risk?
Estimation of late radiation effects in large populations without knowing radiation dose
What is Radiation Hormesis?
Low radiation doses can be beneficial (less than 10 rad)
Relative risk =
Observed Cases
______________
Expected Cases
What is Excess Risk?
Difference between observed and expected number of cases
Excess risk =
Observed cases - Expected cases
What is Absolute Risk?
- At least two different dose levels are known
- Other data, such as # of cases, dose etc are known
- Predicts stochastic radiation response in exposed population
What is the ideal risk?
Absolute Risk
Radiation induced Leukemia follows a…
Linear, non threshold dose response relationship
What is the latent period of Radiation induced Leukemia?
4-7 years
After being exposed to radiation how long are you at risk for acquiring Leukemia?
20 years
Who provided the greatest amount of information about radiation induced leukemia in humans?
Atomic bomb survivors
Do radiologists have an elevated risk of Leukemia?
No
Patients started to develop Leukemia after being treated with radiation for what?
Ankylosing Spondylitis
Can radiation cause cancer?
Without question
What are types of cancer associated with radiation:
- Thyroid cancer
- Bone cancer
- Skin cancer
- Breast cancer
- Lung Cancer
- Liver cancer
What is the risk of death from radiation induced malignancy
5/100 or 0.05%
What is the at risk period after exposure to radiation?
20-25 years
Overall absolute risk for induction of malignancy is approximately…
8 caser per 100 Sv
What are the concerns of radiation effects before pregnancy?
Interrupted Fertility
What are the concerns of radiation effects during pregnancy?
Congenital effects on newborns
What are the concerns of radiation effects after pregnancy?
Suspected genetic effects
During pregnancy, what is the most radiosensitive period?
1st trimester
Low dose chronic irradiation does not impair fertility? T/F
True
The effects of irradiation in utero are time and dose related? T/F
True
What are the possible effects of irradiation in utero?
- Prenatal death
- Neonatal death
- Congenital abnormalities
- Malignancy induction
- Growth impairment
- Genetic effects
- Mental retardation
Out of all the possible effects of irradiation in utero, which one stays constant?
Leukemia
Within (2) weeks of fertilization, what can high radiation doses cause?
Spontaneous abortion (miscarriage
What dose level can cause a 0.1% spontaneous abortion rate?
10 rad dose
What is the normal chance of spontaneous abortion without radiation?
25-50%
What period of time is of least concern because the response is all or none?
The first 2 weeks
What weeks of pregnancy is the period of major organogenesis?
Weeks 2-12
What two effects during pregnancy can occur as a result of radiation exposure?
- Skeletal and organ abnormalities
2. Congenital abnormalities of the CNS
An Oxford survey (1946) found that childhood malignancy is associated with…
Irradiation in utero
The relative risk of childhood leukemia after irradiation in utero is…
1.5, which is a 50% increase
What does radiation exposure in utero do?
Retards the growth and development of the newborn
How often does a 10 rad dose occur in radiology?
Very rarely
Radiation exposure in utero can result in what?
Microcephaly (small head) and mental retardation
What was Muller’s study on genetic effects about?
Fruit flies were irradiated to determine if radiation altered mutations
What did Muller’s study conclude?
That radiation does not alter the quality of the emulations, but did increase the frequency of the mutations
Muller’s study concluded that…
Irradiation did not alter quantity, but frequency
What was Russell’s study?
He irradiated a large mouse colony with different doses of radiation
What did Russell’s study show?
- A dose rate effect does exist
- Confirmed the linear, non threshold dose response relationship
What is doubling dose?
The dose of radiation that produces twice the frequency of genetic mutations as would have been observed without the radiation
What is the doubling dose in humans?
50-250 rad (0.5-2.5 Gy t)
If 7% of the offspring in each generation are born with mutation, the doubling dose eventually increases the number of mutations to how many?
14%
Are radiation doses used occupationally or medically, responsible for any effects on fetal growth or development?
No
Congenital abnormalities mentioned in this chapter are based on…
Doses greater than 100 rad
What does a high dose of radiation over a short period of time result in?
Early effects
What are radiation protection guidelines based on?
Stochastic effects
