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Huda > Chapter 5 Radiation Risks > Flashcards

Chapter 5 Radiation Risks Flashcards

1
Q

direct action

A

Compton and PE electrons ionize molecules

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2
Q

indirect actions

A

compton/PE electrons interact with water to produce free hydroxyl radicals that are chemically reactive

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3
Q

how much damage is caused dy direct vs indirect action

A

2/3 by indirect action
1/3 by direct action

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4
Q

why are mammalian cells easier to kill than bacteria?

A

hey have more DNA
the more DNA = the easier to inactive biological system
bacteria easier to kill than viruses

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5
Q

dose required for sterilization

A

20,000 Gy

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6
Q

what is radiobiology

A

studies effects of ionizing radiation in cells and animal models

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7
Q

single strand vs double strand breaks

A

single strand is most likely repaired, double strand more likely to result in cell death, carcinogenesis, mutation

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8
Q

what can damaged somatic cells do?

A

Induce cancer
-takes years or decades to develop

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9
Q

what happens to cells at lower vs higher doses

A

lower doses: cells more likely to undergo modification
higher doses: cells more likely to be killed

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10
Q

what can damaged sperm and egg cells lead to?

A

hereditary effects
changes in genetic code of a germ cell can affect future generations

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11
Q

what does cell killing depend on?

A

LET of radiation
dose rate (higher = more kill), repair can occur when delivery is protracted
fractionation (reduces cell kill- helps protect normal tissues)
oygenation (2-3 X more sensitive than anoxic cells)

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12
Q

what does law of bergonie and tribondeau state?

A

highest sensitivities occur when cells are undifferentiated and have high mitotic rates
therefore rapidly proliferating cells (ex bone marrow stem cells) are sensitive whereas highly differentiated and non-proliferating cells (ex neurons) are least sensitive

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13
Q

are peripheral lymphocites sensitive to radiation?

A

YES
even though they are differentiated and don’t divide
(they are an exception)

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14
Q

why are oxygenated cells more sensitive than anoxic cells?

A

oxygen prolongs lifetime of free radicals, promoting bond breaking

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15
Q

deterministic effects

A

have a treshold dose
-for doses below treshold, effect won’t occur, for doses much above, effects are expected to occur in all exposed individuals
severity may increase with increasing dose

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16
Q

examples of deterministic effects

A

skin burns
epilation
eye cataracts
sterility

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17
Q

stochastic effects

A

have no treshold dose
-pertain to carcinogenesis and induction of hereditary effects in offspring of exposed individuals
-severity is independent of radiation dose
-dose only affects probability of effect occurring

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18
Q

lethal uniform whole body dose

A

5 Gy

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19
Q

how do you triage the severity of acute radiation exposures?

A

-peripheral lymphocyte count
-immediate diarrhea, fever, hypotension

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20
Q

what whole body dose sterilizes stem cells

A

2 Gy
reduces circulating blood elements within 2-3 weeks
hematopoietic syndrome

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21
Q

what is LD50

A

uniform whole body dose that kills 50% of population
3-4 Gy without medical intervention
-at whole body doses above 8 Gy, absence of immune system means survival is very unlikely

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22
Q

what would whole body doses of > 10 Gy do?

A

lilely kill everyone in 5-10 days due to loss of epithelial lining of GI tract (GI syndrome)

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23
Q

what would whole body dose of 100 Gy do

A

kill everyone in 1-2 days from permeability changes in brain blood vessels (cerebrovascular syndrome)

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24
Q

peak skin dose

A

-usually occurs where radiation enters patient
-used to predict likelihood of skin burns

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25
Q

is exposed skin area taken into account when predicting burns?

A

No

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26
Q

time scales for onset of skin deterministic effects

A

prompt: < 2 weeks
early: 2-8 weeks
mid term: 6-52 weeks
long term: > 40 weeks

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27
Q

peak skin dose levels with effects

A

< 2 Gy : no effects
2-5 Gy: erythema possible (prompt or early)
5-10 Gy: for sure erythema (prompt or early), prolonged erythema may occur mid-term, with dermal atrophy or induration long term
10-15 Gy: prompt erythema + early dry/moist desquamation; mid-term erythema, long term dermal atrophy, induration, telangiectasia, weak skin
> 15 Gy: prompt erythema, edema, acute ulceration, mid term dermal atrophy, secondary ulceration, dermal necrosis; long term includes telangiactasia, dermal strophy or induration, skin breakdown likely requiring surgery

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28
Q

national cancer institute categorization of radiation-induced skin injuries

A

grade 1, 2-10 Gy, faint to moderate erythema
grade 2, 5-15 Gy, erythema
grade 3, > 10 Gy, moist desquamation in areas other than skin folds and creases
grade 4, > 15 Gy, skin necrosis or ulceration of full-thickness dermis

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29
Q

epilation

A

occurs temporarily for scalp dose of 3-5 Gy after 2-3 weeks
(regrowth of hair starts 2 months after irradiation, may be gray)
for dose > 7 Gy epilation likely permanent

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30
Q

what are cataracts

A

opacification of eye lens normally transparent
eye lens has no way of removing dead or damaged cells
-cataracts caused by radiation migrate to posterior pole of lens

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31
Q

treshold dose for cataracts

A

per up to 2011:
2 Gy for acute
5 Gy for chronic

now ICRP considers treshold to be 0.5 Gy for acute and chronic

32
Q

latency period of cataracts

A

several years after eye lens doses of a few Gy
-as doses increases, latency periods may get shorter

33
Q

dose tresholds for sterility

A

0.2 Gy- diminished sperm count
0.5 Gy- azoospermia (temporary sterility, recovery can be 3 years)
6 Gy- permanent sterility

34
Q

is acute or fractionated exposure in gonads worse in males?

A

fractionated
permanent sterility can result from 3 Gt fractionated over a few weeks

35
Q

doses for sterility in females

A

depend on age
10 Gy in pre-puberty
2 Gy in premenopausal women

36
Q

what is main concern following exposure to radiation below the treshold of deterministic effects?

A

carcinogenesis

37
Q

how are links between exposure and ionizing radiation established?

A
38
Q

what do epidemiologic studies require?

A

-large cohorts
-control groups
-long follow-up periods

39
Q

who is usually studied for epidemiological studies?

A

-A bomb survivors
-radiation workers
-patients exposed to high doses from therapeutic x-rays

40
Q

what do excess cancer deaths depend on?

A

dose
age at exposure
time since exposure
gender

41
Q

where have excess cancers been observed for high dose?

A

-lung cancer in miners
-bone sarcomas and nasopharynx cancers in dial painters
-skin cancers in radiologists, dentists, when safety was lax
-cancer following radiotherapy for lymphoma, breast cancer
-secondary cancers following radiation therapy for chilhood cancer
-breast cancer in women who underwent fractionated fluoroscopy

42
Q

where have excess cancers been observed for high dose?

A

-thyroid cancer in kids treated for tinea capitis
-10 mGy to uterus= childhood cancer
-cancer in bomb survivors exposed to only 30 mGy
-leukemia and brain tumours in children who underwent CT
-

43
Q

for whom is thyroid cancer more likely?

A

women, children

44
Q

what organs are most susceptible to radiation-induced malignancy

A

bone marrow, colon, lung, breast, stomach, childhood thyroid

45
Q

moderately radiosensitive organs

A

bladder, liver, esophagus

46
Q

what is latency

A

time between irradiation and appearance of malignancy

47
Q

latency period for leukemia

A

few years
at least 2 years

48
Q

latency period for solid tumours

A

decades
at least 5 years

49
Q

what model is used for cancer risk estimates in diagnostic imaging?

A

linear no treshold model

50
Q

beneficial effect of radiation

A

hormesis
not accepted as an excuse for radiating someone

51
Q

what is BEIR

A

Biologic Effects of Ionizing Radiation
US comittee that provides detail on radiation risks
-similar risk estimated to UNSCEAR and ICRP

52
Q

what is UNSCEAR

A

UN Scientific committee on effects of atomic radiation - similar risk estimates to BEIR and ICRP

53
Q

what is ICRP

A

International Commission on Radiological Protection
-similar risk estimates to BEIR and UNSCEAR

54
Q

are males or females more radiosensitive?

A

females, by 70 %
-breast and lung cancer account for these differences

55
Q

newborns are how much more radiosensitive than 25 year olds?

A

3 X
seniors are 3 X less sensitive than 25 year olds

56
Q

how much are we likely over or underestimating radiation risks?

A

2-3 X

57
Q

what is the risk of cancer for an american who isn’t exposed to radiation

A

40 %

58
Q

how do hereditary effects occur?

A

-irradiation of germ cells involved in reproduction
-stochastic process with no treshold
-radiation increases incidence of mutations that occur spontaneously

59
Q

is there epidemiological evidence of hereditary effects in exposed humans?

A

No
-children of A bomb survivors did not show effects
-all data comes from animal studies

60
Q

types of hereditary effects

A

mendelian
chromosomal
multifactorial

61
Q

ICRP hereditary risk

A

0.2%/Gy to the 2nd generation for the whole population
0.1%/Gy for the working population since this excludes children

62
Q

what percent of spontaneous mutations in humans is due to natural background radiation?

A

a few percent

63
Q

what is doubling dose

A

-absorbed dose to gonads of whole population that would double the spontaneous mutation incidence
1-2 Gy

64
Q

hereditary effects account for what % of total detriment when populations are irradiated

A

8 %
i.e. Wt of 0.08 for gonads

65
Q

how is gestation in humans divided?

A

pre-implantation (conception to 9 days)
organogenesis (10 days to 6 weeks)
fetal (6 weeks to term)

66
Q

what can happen to fetus given exposure to radiation?

A

nothing if exposed before fertilization
-radiation can result in death to fetus
-congenital malformations if exposed during organogenesis
-can get growth retardation and mental retardation
-depends on gestational age and amount of radiation received

67
Q

what is background incidence of congenital abnormalities in US in absence of any radiation

A

5 %

68
Q

who offers advce on deterministic risks at different levels of radiation exposure?

A

ACR practice guideline for imaging pregnant women

69
Q

deterministic risk to fetus for dose < 50 mGy

A

-no risk

70
Q

deterministic risk to fetus for dose 50-100 mGy

A

-scientifically uncertain
-may be too subtle to be detected

71
Q

deterministic risk to fetus for dose > 100 mGy

A

-deterministic effect may occur
-embryo death during pre-implantation
-major malformations during organogenesis
-reduced head size and mental impairment most likely during 8-15 week gestational age, with much lower risk for 16-25 weeks

72
Q

dose for risk of carcinogenesis in the fetus

A

10 mGy, especially during 3rd trimester

73
Q

plot of deterministic effect and childhood cancer incidence as a function of dose

A

for deterministic, x goes from 100-10,000 mGy, risk goes from 0 (100) to 50 (1,000) to 100 (10,000) in a sigmoid shape

for chilhood cancer, x goes from 0 to 100 mGy
risk increases as straight lie from 0.2 (at 0 mGy) to 1 (at 100 mGy)
0.2 % at 0 mGy is background childhood cancer incidence

74
Q

what has been used for radiation protection purposes regarding carcinogenesis due to exposure of fetus

A

-for dose of 25 mGy, risk of 0.2% of childhood cancer
-likely reasonable during 3rd trimester but conservative during 1st and 2nd trimester

therefore, a scan that delivers 25 mGy to fetus doubles the likelihood of childhood cancer since background incidence is 0.2 %

75
Q

when is radiation induced erythema likely to be observed after skin is exposed?

A

10 days
most lilely to occur for peak skin dose of 5 Gy or more

76
Q

for a population exposed to uniform whole-body doses, genetic defects are currently estimated to contribute what % to the total detriment?

A

8% because wt = 0.08

Huda (20 decks)

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