Stochastic Effects Flashcards by F S

Results of low doses delivered over long period

Stochastic Effects

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Experienced low dose and low linear energy transfer

Radiation workers

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Delivered intermittently over long periods

Patient radiation doses

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Principal stochastic effects consists of

Radiation induced malignancy

Genetic Effects

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Reports of local tissue effects and life-span shortening

Not Significant

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Stochastic effects are assumed as a

linear non-threshold dose-response relationship

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Radiation exposure in diagnostic radiology are _____ because they are delivered over ______

Chronic

Long periods

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Stochastic effects exhibit an increasing incidence of response with

increasing dose

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Stochastic dose-response relationship is _____

linear

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Chronic irradiation of the skin can result in

severe nonmalignant changes

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Observed among radiologist who performed fluoroscopic examination without protective gloves

Radiodermatitis

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Characterized by callused, discolored, and weathered appearance to the skin

Radiodermatitis

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Can be produced as both deterministic and a stochastic response

Chromosome damage in circulating lymphocytes

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Physicist developed radiation induced cataracts due to

very high radiation doses to the lens of the eye

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Radiation induced cataracts occurs on the

posterior pole of the lens

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Radiosensitivity of the lens of the eye is

age dependent

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As the age of the individual increases,

Radiation effects become greater

Latent period becomes shorter

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Latent Period of cataracts

5 to 30 years;

Average of 15 years

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Dose-response relationship for radiation induced cataracts

Nonlinear, threshold

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Relationship between life span shortening and dose appears

linear, nonthreshold

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Humans expect reduced life span of

approx. 10 days for every 10mGyt

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Radiation induced life span shortening is

nonspecific

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Life span shortening occurs simply as

accelerated premature aging

death

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Precise dose-response relationships are often not possible to formulate and resort to

Risk estimates

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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