Stochastic Effects Flashcards
The principal stochastic effects of low-dose radiation over long periods consist of
Radiation induced malignancies and genetic effects
Radiation protection guides are based on
Suspected or observed stochastic effects of radiation
With increasing dose, stochastic effects of radiation exposure exhibit
And increasing incident response, not severity.
Stochastic effects of radiation follow what type of dose response relationship
Linear, non-threshold
Epidemiologic studies
Are required when the number of people affected is small
Studies of large numbers of people exposed to a toxic substance require considerable statistical analysis
What are two reasons that epidemiologic studies of people exposed to radiation are difficult
The dose usually is not known but is presumed to be low.
The frequency of response is very low.
Radiodermatitis
Stochastic effect of skin.
Dose to produce the effect is very high.
Early radiologist who performed fluoroscopy without protective gloves developed very calloused, discolored and weathered appearance to the skin of their hands and forearms. The skin would be very tight, brittle, severely cracked or flake.
Irradiation of blood forming organs can produce —- as a deterministic response or —– as a stochastic response.
Hematologic depression
Leukemia
Cyclotron
A 12 cm diameter device capable of accelerating charge particles to very high energy.
How did cyclotron physicist get cataracts
They received high radiation doses to the lens of the eye because they had to look directly into the beam
The radiosensitivity of the lens of the eye is — dependent
Age
As the age of the individual increases, the radiation effects become greater and the latent. Becomes shorter
Latent periods for radiation induced cataracts
5 to 30 years
High LET radiation, such as —-, has a high relative biological effectiveness RBE for the production of cataracts.
Neutron and proton radiation
If the lens does exceeds — Cataracs develop in 100% of those irradiated
10 Gy
For radiation workers life is shortened by
12 days
Since dose response relationship are not possible to formulate for late response effects of earlier radiation exposure we resort to
Risk estimates
Three types of risk estimates
Relative
Excess
Absolute
If one observes a large population for stochastic radiation effects without having any precise knowledge of the radiation dose to which they were exposed, then —- risk is used
Relative
The relative risk is computed by comparing the number of persons—
In the exposed population showing a given stochastic effect with the number in an unexposed population who show the same stochastic effect.
A relative risk of 1.0 indicates
No risk at all
A relative risk of 1.5 indicates that the frequency of a late response is
50% higher in the irradiated population then in the non-irradiated population
A relative risk of less than 1 indicates
That the radiation exposed population receives some protective benefit.
The theory of radiation hormesis suggests that radiation less than — is good for you because ?
100 mGY
Stimulates molecular repair and immunologic response mechanisms
When an investigation of human radiation response reveals the induction of some Stochastic effect, The magnitude of the effect is reflected by
The excess number of cases induced
Excess risk is calculated
Observed cases - expected cases
If at least two different dose levels are known, then it may be possible to determine —- risk factor
Absolute
The absolute risk of total radiation induced malignant disease has been determined by who
National Academy of Science (NAS) Committee on the Biologic Effects of Ionizing Radiation (BEIR)
The absolute risk of total radiation induced malignant disease, value is
8 x 10^-2 Sv^-1
The absolute risk of a fatal radiation induced malignant disease, value is ? What is this used to predict?
5 x 10^-2 Sv-1
This risk coefficient is used to predict stochastic radiation response in exposed populations
To determine the absolute radiation risk, one must assume a —- dose response relationship.
Linear
The value of the absolute radiation risk is equal to the
Slope of the linear, non-threshold dose response relationship.
Types of radiation induced malignancies include
Leukemia
Cancers : bone, lung, liver, breast
Relative risk =
Observed cases/expected cases
Excess Risk =
Observed cases - Expected cases
When an investigation of human radiation response reveals the induction of some stochastic effect, the magnitude of the effect is reflected by the ______ number of cases induced.
Excess
NAS BEIR is
National Academy of Science Committee on the Biologic Effects of Ionizing Radiation
Absolute risk =
(Risk factor) x (dose) x (# of population)
Absolute risk value for non-fatal radiation-induced malignancy
8 x 10^-2 Sv^-1
Effective dose units is
Sb
Absolute risk value for fatal radiation-induced malignant disease
5 x 10^-2 Sv^-1
1mSv= __ Sv
0.001
0.5mSv= __Sv
0.0005 Sv
Tuberculosis was treated with?
Non-image intensified fluoroscopy, up to several hundred tx.
The relative risk for the tuberculosis pts, for developing breast cancer was as high as
10:1
Patients treated for postpartum mastitis with doses 0.75 to 10 Gy, the relative risk for breast cancer
3:1
A-bomb survivors relative risk for breast cancer
4:1
Absolute Risk for radiation-induced breast cancer
6 x 10^-2 Sv-1
Uranium miners in the 50s and 60s had and in lung cancer because
Uranium decays to Radon
Decays to lead
Alpha particles are high LET radiation and high RBE
Over 4,000 uranium miners receives doses to lung, up to 30 Gy. Relative Risk for lung cancer?
If they were smokers?
8: 1
20: 1 (8 times higher)
______ was contrast agent used in angiography, which caused Liver Cancer.
Thoratrast
Radioactive isotopes of thorium
Thorium dioxide
Latent period for liver cancer caused by thorotrast.
15 to 20 years
Thorium dioxide particles are deposited
In phagocytic cells of the reticuloendothelial system and are concentrated in the liver and spleen
The alpha rays from he radioactive isotopes of thorium, have ____ LET
High
Physical aspect/ absorbed dose
Gray
Biological aspect/effective dose
Sv
Risk of death from rad-induced malignant disease
5 cases/100Sv
At risk period for risk of death from rad-induced malignant disease
20 to 25 years
Effective dose of 10 mSv has a risk of ___ for malignant disease induction, half will die
10 mSv
3 mile island
1979 2 million population Natural incidences of cancer is 300,000 15uGy Dose estimates expect additions cases 1.5 additional cases
BEIR Committee
Biologic Effects of Ionizing Radiation
Reviewed the data on stochastic effects of low-dose, low LET radiation.
One of the situations BEIR examined
They estimated the excess deaths from malignant disease after a 1 time accidental exposure to 10 mGy.
800 cases
100,000 population
Absolute Dose 8 x 10 ^-2 Sv^-1
BEIR considered the response to a dose of 10 mGy/year for life; what population?
A very busy IR Rad guy
BEIR considered excess rad.-induced cancer death after a continuous dose of 1 mGy/year for life.
For who?
Us and general public
Excessive risk= 550 deaths/100,000 people
This is in addition to the normal incidence f cancer deaths of 20,000 per 100,000 people
BEIR analyzed human data with regard to
- Age at exposure
- A limited time of expression of effects
- Whether the response was absolute or relative
If one is irradiated at an early age, and the response time is limited, rad-induced excess mal disease appears as a ?
Bulge on the age response relationship
Absolute age-response relationship
Predicts that the excess rad-induced cancer risk is constant for life.
Relative Risk
Predicts that the excess rad induced cancer risk is proportions to the natural incidence.
Increase is likely as age increases.
Does low dose impair fertility
No
Higher doses of radiation 100mGy during 1st 2 weeks of pregnancy
.1% rate of loss of preg
Natural loss of pregnancy
20 to 50% in 1st 2 weeks
After 2nd week to 12th week of pregnancy, with high rad dose
Major organogenesis, radiosensitive.
Can get congenital defects with high dose.
Skeletal or organ abnormalities
In mice during the early pregnancy:
Dose of 2 Gy, nearly 100% of fetuses……
And 80%….
Dose under 100mGy….
- Significant abnormalities
- Died
- No observable effects
What did the Oxford Survey findings indicate for rad-induced leukemia
A relative risk of 1.5 for the development of childhood leukemia after irradiation in utero is significant.
This indicates an increase of 50% over the nonirradiated rate.
A finding in offspring of A-Bomb survivors
Mental retardation
A 100mGy dose in utero s expected to increase the incidence to an additional 0.5%
Relative risk of childhood leukemia after irradiation in utero by trimester
- First trimester
- Second trimester
- Third trimester
- 8.3
- 1.5
- 1.4
Effects after 100 mGy in utero
- 0-2 weeks
- 2-10 weeks
- 2-15 weeks
- 0-9 months
Increase of response to radiation: 1. 0.1% spontaneous abortion 2. 1% congenital abnormalities 3. 0.5% Mental retardation 4. Malignant disease 12/10,000 Impaired growth and development nil Genetic mutation nil
We do not have any data that suggest that radiation -induced genetic effects occurs in humans, so most of the data is from?
Large scale experiments with flies and mice
Geneticist, H.J. Muller reported the results of his irradiation of Drosophilia, the fruit flies and genetic effects to be
Linear, nonthreshold.
Radiation does not alter the quality of mutations but increases the frequency of those mutations
That such mutations were single-hit phenomena
On the basis of Muller’s work, the NCRP in 1932 lowered?
The recommended dose limit and acknowledged officially the existence of nonthreshold radiation effects.
Since then, all rad protection guides have assumed a linear, nonthreshold DRR
The only other significant genetic experiment was ?
Russell’s experiment on mice
