biological effects of rad Flashcards
Modulator
LET =
linear energy transfer = dE/dl… energy deposited per unit length
high LET = lots of concentrated damage
low results in scattered damage
Modulator
RBE= ?
radiological biological effectiveness
have same biological endpoint- comparison of source to reference
RBE = D ref/ D test
RBE ~ QF ~ Wr
modulator
mitotic cell cycle
most sensitive M and G2
least in late S phase
linear and quadratic effects are equal at…
D = alpha/beta
Modulator
Fractionated Radiation
Repair of normal tissue
reassortment
but, could have repopulation if interval too long
Modulator
Dose Rate
low dose…a little over time
high dose causes more damage more quickly
Modulator
Oxygen effect
low LET radiation have higher effect
presence of oxygen sets the damage
Radiation carcinogenesis
it is, esp. at high doses and high dose rates.
good epidemological evidence for acute exposures above 0.2 to 5 Gy
Inversely correlated to age at exposure
females more sensitive
minimum latency…
~ 3 yrs leukemia, 4 yrs bone, 5 yrs thyroid, 10 yrs solid
Mean latency about 20-30 yrs
reports
icrp 99
BIER VII
icrp 103. Tissue weighting factors update
preston, et. al….good report on organs
heritable effects?
not detectable
In Utero
sources… lou wagner wrote the book, or Brent
most risk…1 st trimester
No malformations 100-1000 mGy 3rd trimester
Termination of pregnancy at
cataracts
operative cataract odds ratio of 1.4 at 1 Gy
dose threshold seen at 0.1 Gy- upper bound of 0.8 Gy
ICRP 2011 statement on tissue reaction says lens of eye threshold to be 0.5 GY ( limit to 20 mSv/yr averaged over 5 yrs. No single year > 50 mSv)
cardiovascular
RT patients effects 1-2 Gy show risk 10-20 yrs later
circulatory disease threshold is now 0.5 Gy to heart or brain per ICRP 2011 statement on tissue reactions
Tissue and organ sensitivities
no functional impairment…
Background rad in us
~ 6.3 mSv/y with med component
~ 2 mrem/ day
Typical general radiology doses
dental
dental... 0.05 mSv Chest... 0.1 mSv Head... 0.1 mSv Mammography...0.7 abdomen...1.2 mSv pET CT ( CT only)...0.72 mSv head CT... 2 mSv chest...7 mSv abdomen or pelvis...10 mSv CT angiograpy...13 mSv
typical nuclear med
f-18…9 mSv
i-131… 1 mCi 7.5 mSv
tc-99…5 mSv
i-131 therapy…270 mSv
Low dose
10 cGy..
below a different group of genes repair damage than the group that repairs higher dose damage
expanded paradigm
production of damage is linear
Response to damage is not- different sets of genes
Risk
whole population… 5.5% per Sv
adult…4.1% per Sv
Less than ~0.2 Sv… no evidence of any effects
Not for individuals
Aapm PP-25a less than 50mSv don’t use
Effective dose- can you use for an individual?
Additional problem with literature…
NO!… it is from average man/woman values to phantoms
When you see effective dose, there is no mention of which icrp report they used…26, 60, or 103… weighting factors change
effective dose calcs- how accurate?
order of magnitude!
don’t use decimals…no meaning as accuracy is not good…
Can use to see if doses go up or down.
if effective dose cannot be used to assess risk, what can?
effects at low doses require hugh cohorts to assess effects…bomb survivors not that numerous.
had some rad workers that meet numbers…not suitable via BEIR. Bottom line…lots of uncertainty- giving a number is silly.
LNT- 2006 French Academy of Sciences
LNT relationship is inconsistent with radiation biologic and experimental data
Damage is linear, but biological response is not
Hall
Below 100 mSv, it has not been proven there is any risk.
LNT is used to estimate risk for occupational purposes.
Cannot predict from the data
