Stochastic Effects Flashcards
Results of low doses delivered over long period
Stochastic Effects
Experienced low dose and low linear energy transfer
Radiation workers
Delivered intermittently over long periods
Patient radiation doses
Principal stochastic effects consists of
Radiation induced malignancy
Genetic Effects
Reports of local tissue effects and life-span shortening
Not Significant
Stochastic effects are assumed as a
linear non-threshold dose-response relationship
Radiation exposure in diagnostic radiology are _____ because they are delivered over ______
Chronic
Long periods
Stochastic effects exhibit an increasing incidence of response with
increasing dose
Stochastic dose-response relationship is _____
linear
Chronic irradiation of the skin can result in
severe nonmalignant changes
Observed among radiologist who performed fluoroscopic examination without protective gloves
Radiodermatitis
Characterized by callused, discolored, and weathered appearance to the skin
Radiodermatitis
Can be produced as both deterministic and a stochastic response
Chromosome damage in circulating lymphocytes
Physicist developed radiation induced cataracts due to
very high radiation doses to the lens of the eye
Radiation induced cataracts occurs on the
posterior pole of the lens
Radiosensitivity of the lens of the eye is
age dependent
As the age of the individual increases,
Radiation effects become greater
Latent period becomes shorter
Latent Period of cataracts
5 to 30 years;
Average of 15 years
Dose-response relationship for radiation induced cataracts
Nonlinear, threshold
Relationship between life span shortening and dose appears
linear, nonthreshold
Humans expect reduced life span of
approx. 10 days for every 10mGyt
Radiation induced life span shortening is
nonspecific
Life span shortening occurs simply as
accelerated premature aging
death
Precise dose-response relationships are often not possible to formulate and resort to
Risk estimates
Computed by comparing the number of persons in the exposed population showing a given stochastic effects with the unexposed population who show same stochastic effects
Relative Risk
Formula for relative risk
Relative Risk = Observed cases/Expected cases
Relative risk of 1
no risk at all
Relative risk of 1.5
frequency of the late response is 50% higher in the irradiated population
Relative risk for stochastic effects ranges to
1 to 2
Relative risk less than 1
“very low radiation doses are beneficial” ; theory of hormesis
Low doses of radiation approx. 100mGyt, may provide
Stimulating molecular repair
Immunologic response mechanism
Used when an investigation of human radiation response reveals the induction of some stochastic effects
Excess risk
Known to occur spontaneously in nonirradiated population
Leukemia
Formula for excess risk
excess risk= observed - expected cases
used if atleast two different dose levels are known
Absolute risk
Absolute risk consists of units of
cases/population/dose
Absolute risk of a fatal radiation induced malignant disease
5 x 10^-2 Sv^-1
The incidence of radiation-induced leukemia
increases with increasing radiation dose
The form of the dose-response relationship of leukemia is
linear and nonthreshold
Atomic Bomb Casualty Commission (ABCC) now known as
Radiation Effects Research Foundation (RERF)
Radiation induced leukemia is considered to have a
latent period of 4 to 7 years
at-risk period of approx. 20 years
the time after irradiation during which one might expect the radiation effect to occur
at-risk period
At-risk period of radiation induced cancer
Lifetime
Observed most often among atomic bomb survivors
Acute leukemia
Chronic myelocytic leukemia
Not considered to be a form of radiation -induced leukemia
Chronic lymphocytic leukemia
Overall relative risk of leukemia is
approx. 3:1
a deficiency in the production of red blood cells through lack of vitamin B12
Pernicious anemia
Some of the early radiologist received doses exceeding
1 Gyt/yr (100 rad/yr)
Arthritis like condition of the vertebral column
Ankylosing Spondylitis
Records show that the dose to the bone marrow of the spinal cord ranged from
1 to 40 Gy (100 to 400 rad)
Relative risk (patient w/ ankylosing spondylitis) is
10:1
Ionizing radiation can cause
cancer
First two groups irradiated in thyroid gland during childhood
Ann Arbor series
Rochester series
Dose used in order to shrink an enlarged thyroid
5 Gyt (500rad)
Subjected to high levels of radioactive fallout during hydrogen bomb test
21 children in Rongelap Atoll (1954)
Radiation dose received by the children from both external exposure and internal ingestion
approx 12Gyt (1200rad)
Two population groups have contributed an quantity of data that radiation can cause bone cancer
Radium watch-dial painters
Patients treated with radium salts for arthritis to tuberculosis
This would continuously excite the luminous compounds so the watch dial would glow in the dark
Radium salts (alpha and beta particles)
Radium’s half life
1620 years
Doses received by the dial painters
500 Gyt (50,000 rad)
Overall relative risk for the radium watch-dial painters
122:1
Radiation-induced skin cancer follows a
threshold dose-response relationship
Latent period (skin cancer)
approx 5 to 10 years
At dose delivered to the skin i n the range of 5 to 20 Gyt, relative risk is
4:1
if the dose was 40 to 60 Gy
or 60 Gy to 100 Gy, relative risk was
14: 1
27: 1
Relative risk for radiation-induced breast cancer is
10:1
Radiation-induced breast cancer developed in patients treated for
acute postpartum mastitis
Dose to the patients ranged from
0.75 to 10 Gyt
Relative risk factor in this population
approx 3:1
Radiation induced breast cancer has been observed among
atomic bomb survivors
Approx 50% of workers died of lung cancer in
Bohemian pitchblende mines of Germany
Cause of death for the bohemian pitchblende workers
radiation exposure from radon in the mines
Decay product of uranium
radon (222Rn)
Dose to lung tissue as high as 30Gy (3000 rad), relative risk is
8:1
Smoking uranium miners have a relative risk of
approx. 20:1
Thorium dioxide (ThO2) in a colloidal suspension known as
Thorotrast
Thorotrast is responsible for several types of carcinoma after a latent period of
approx. 15 to 20 years
Overall absolute risk for induction of malignancy is
approx 8 cases/100 Sv
at-risk period for 20 to 25 years
Risk of death from radiation-induced malignant disease
5/100
Three Mile Island incidemt result to
no more than two additional malignant deaths
Areas of concern
Before pregnancy:
Interrupted fertility
Areas of concern
During pregnancy:
Possible congenital effects in newborns
Areas of concern
Postpregnancy:
Suspected genetic effects
Low dose chronic irradiation
Does not impair fertility
Two types of radiation exposures
Radiation worker
Patient
Rapidly developing cell system, particularly sensitive to radiation
Embryo
Most radiosensitive period during pregnancy
First trimester
If radiation-induced congenital abnormalities are severe enough results will be
Neonatal death
a dose of 2 Gyt (200rad) to the mouse
100% of fetuses suffered significant abnormalities
Relative risk of childhood leukemia after irradiation in utero is
1.5
Unexpected finding in the offspring of atomic bomb survivors
Mental retardation
Irradiation in utero has been associated with
Microcephaly (small head)
Mental retardation
Weakest area of knowledge in radiation biology is the area of
Radiation genetics
Nobel prize-winning geneticist H.J Muller from University of Texas reported the results of
Irradiation of Drosophilia
Dose-response relationship for radiation-induced genetic damage
Linear non threshold
Muller’s concluded that mutations were
Single-hit phenomena (no fractionation effects)
All radiation protection guides have assumed a
Linear, nonthreshold dose response relationship
A large mouse colony which was exposed to radiation dose rates from 0.001 to 0.90 rad per minute and total doses of 1000rad (10 Gy)
Megamouse Project
Dose of radiation that produces twice the frequency of genetic mutations as would have been observed without the radiation
Doubling Dose
Mutation rate depends upon the rate at which the dose is given
Dose-rate effect
