Unit 5 - Stochastic Effects

epidemiology

studies of large #s of people exposed to toxic substances

deals w/ the incidence, distribution & control of disease in populations

consists of observations & statistical data analysis

stochastic effects

probabilistic → random chances

effects that exhibit an increase incidence of response (not severity) w/ increasing dose

no dose threshold

linear relationship

late effects

biologic damage appear months or years after exposure

principle are radiation induced malignancy & genetic effects → abnormal functioning cells

most assume linear, nonthreshold dose response

carcinogenesis

cataractogenesis

embroyologic effects

what are types of late effects?

radiation in digital imaging

low exposures → no specific dose

low LET

chronic in nature bc delievered intermittently over long periods

absolute & relative risk forecasts

number of excess concerns that would not have occured in the population in question w/out exposure to ionizing radiation

absolute risk

estimates a specific # will occur as a result of exposure

specific = direct chance that an event will happen

must known at least 2 dose levels

NOT compare to populations

relative risk

predicts that the # of excess cancers will increase as the natural incidence of cancer increases

by observing large populations for late effects w/out any precise knowledge of the dose they were exposed to

mostly used risk estimate model

how is relative risk measured?

observed cases (exposed) / expected case (unexposed)

what is the formula for relative risk?

no risk

if the relative risk is 1, what is the outcome?

late effects are 50% higher

if the relative risk is 1.5, what is the outcome?

300% increase

if teh realtive risk is 4, what is the outcome?

radiation hormesis

(stimulated moecular repair)

if the relative risk is < 1, what is the outcome?

excess risk

the difference between the observed # of cases & expected # of cases

total observed

oberved - expected

what is the formula for excess risk?

number of cases/dose/population

what does absolute risk units consist of?

BEIR

who determined the amount risk of the total radiation induced malignant disease?

skin cancer

most common in radiologists, technologists & radiation therapy patients

nonlinear, threshold

5-10 years

what is the latent period for skin cancer?

radiodermatitis

what is the first sign of skin cancer?

cataractogenesis

radiosensitivity of the lens is age-dependent

nonlinear, threshold

high LET has high RBE for the production of cataracts

atomic bomb survivors

radiation therapy patients

high energy physicists

who is most likely to be effects by cataractogenesis?

lens

what is the most radiosensitive part of the eye?

cyclotron

machine capable of accelerating charged particles very high energies

15 years

what is the latent period of cataractogenesis?

0.5 Gy (single exposure)

5-10 Gy (chronic fractionated)

what is the current threshold for cataractogenesis?

radiation induce malignancy

lab experiments & epidemiologic studies of human populations

radiation induced cancer occurs in smaller #s then regular occuring cancers

increase dose = increase risk

cancer casues by low level rad can be difficult to identify

leukemia

blood cancer that normall begins in the bone marrow & results in higher #s of abnormal blood cells

linear, nonthreshold

lab animals & atomic bomb survivors

how was leukemia studied?

incidence increase = increase dose

what were the results of lab animals for leukemia studies?

greatest amount of data

latent period → 4-7 years

risk period of 20 years

what were the results of the atomic bomb survivors for leukemia studies?

thyroid cancers

linear, nonthreshold

latent period 5-10 years

women are at more risk then men

Iodine 131

what was the substance the become airborne & concentrating in the thryoid gland to increase thyroid cancer?

radium watch dial painters

radium salt patients

who was mostly effects w/ bone cancer from ingesting radium?

femur, mandible, pelvis

what were the most frequently effected bones by ingesting radium?

TB treatments

postparum mastitis

atomic bomb survivors

what were the groups studied for breast cancer?

lung cancer

what was the most common late effect of Uranium miners?

radon

what substance did uranium miners inhale to cause lung cancer?

radon in homes

what is the 2nd leading casue of lung cancer?

40%

what is the percentage of home in PA have radon levels above EPA action guildine of 4 pico curies per liter?

alpha, beta & gamma

what does radon emit?

thorotrast patients

what types of patients were studies for liver cancer?

contrast agent for angiogrpahy

released alpha, beta, & gamma rays

latent period of 15-20 years

relative risk 10:1

what were the main results of the thorotrast patients for liver cancer?

approx 8 cases per 100 Sv over 20-25 years after exposure

what is the overall absolute risk for the total risk of malignancy?

total risk of malignancy

based on observations on population groups exposed to low-level radiation & risk estimates for leukemia & cancer

5/100

what is the death risk of the total risk of malignancy?

1/10,000

what is the effective dose of 10 mSv equal to the risk of the total risk of malignancy?

Biological Effects of Ionizing Radiation

what does BEIR stand for?

BEIR Committee

review stochatic effects of low dose & low LET

estimated excess mortatlity 3 situations

unlikely in radiology

what is the estimated mortality for 0.1 Gy greater w. a single dose?

possibility in radiology, but rare

what is the estimated mortality for 0.01 Gy/year for life?

considerably higher then most RT

what is the estimated mortality for 0.00 Gy/year coninuous

no increased risk of late effects

if 0.01 Gy may not be harmful, what does that equal to?

20%

what percentage of Americans will die from malignant disease of natural causes?

gondal effects (pre-pregnacy)

interrupted fertility

fetal effects (during pregnancy)

teratogonic/congenital effects

post pregnancy

genetic effects

males & female

high levels effect fertility of

1st trimester

when is the most radiosenstive period of a pregnancy?

embryonic

all life forms most vulnerable during what stage?

teratogenic effect

anything introduced during pregnancy that impacts typical fetla development of a fetus

carcinogensis

lethal effects

malfromations

cerebral effect

what are the effects caused by the teratogenic effect?

lethal effects

what is the most probable effect in the preimplanation stage to occur?

pre-implantation phase (0-9 days)

union of sperm & egg to time zygote embeds in uterus

prenatal death (spontaneous aboration)

all or non response

25-50%

what is the precentage of natural occuring prenatal deaths?

0.1%

what is the precentage of 0.05-0.15 Gy exposure causing prenatal death?

organogensis phase (10 days - 12 weeks)

malformations may occur

growth inhibition

intellectual disability

genital deformities

microcephaly

5%

what percentage of congential abnormalities occur naturally w/out irradiation?

mirocephaly

head circumference 2x smaller than normal

realtively frequent after in uterus gestation < 16 weeks

fetal growth stage (< 3 months)

less differentiating cells

congential abnormalities & disorders may still occur

most evidence from decades of ABS

utero exposure to radionuclides that cross the placenta

radioiodine concentrates primarily in the thyroid gland

thryoid functions at 10 weeks in the fetus

if necessary, only delivered as trace doses before the 10th week of gestation

utero exposure to radionuclides that remain on the maternal side

emits whole body radiation via gamma rays

4%

what is the precentage of birth defects that happen naturally?

during oranogenesis

when it is the easier to predict if exposure had an effect on embryo-feuts during what phase?

genetic effects

biologic effects of ionizing radiation on future generations

damage DNA in parent sperm/ova can lead to passing on faulty infor of offspring

10%

what is the percentage of natural mutation occuring in births?

genetic mutations

mutagens may cause what?

mutagens

viruses & multiple specific chemcials

mice & fruit flies

what was stuided to understand more about genetic effects?

fruit fly

HJ Muller did what experiment?

fruit fly experiment

irradiated mature fruit flies before procreation w/ thousands of radiation

genetic induced damage → linear, nonthreshold

NO alter quality of mutation

Increase the frequency of mutation

recessive & spontaneous

mutations are what type of gene?

NCRP

who lowered the record dose limits & offically acknowledged existence of nonthreshold effects from the fruit fly experiment?

mouse house

Lianne & William Russel did what experiment?

mouse house experiment

dose 0.00001 Gy/min = total dose of 10 Gy

show females are less senstivie than males

confrimed linear, nonthreshold

average mutation rate per unit dose in mouse 15x observed in fruit flies

ICRP

who lowered the tissue weighting factor for gonads?

from 0.2 to 0.08

what did the ICRP lower the tissue weighting factor gonads to?

linearily w/ dose (not threshold)

how does mutation frequency increase?

dose rate (protraction/fractionation)

effects depend on what?

zero

diagnostic imaging for radiation induced genetic mutation is what?