8: Radiation Safety - Mahoney Flashcards
stochastic effects
responses where probability of occurrence increases with dose
- the higher the dose, the greater chance of effects
deterministic/nonstochastic effects
severity of response increases with does
-higher the dose, the more severe the response
do not have a threshold dose and are observed for months or years
stochastic effects
result from low radiation doses over along time
stochastic effects
leukemia, bone, breast and lung CA
cataracts and radiodermatitis
stochastic effects
have threshold dose which needs to be exceeded before response is seen and severity of response proportional to dose
deterministic effects
occur early within min or days
deterministic effects
radiation sickness
skin desquamation
congenital malformations
deterministic effect
most sensitive tissues
bone marrow > lymphocytes > GI
most resistant tissue
CNS
law of bergonie and tribondeau
sensitivity of tissues depends upon proliferative capacity
rapidly dividing cells are more sensitive than slow
fully differentiated cells are less sensitive
4 physical factors affecting radiosensitivity
- LET linear energy transfer (measure of amount of energy transferred along path of radation) (xrays low; alpha particles high)
- relative biological effectiveness (one form of radiation compared to another)
- protraction ( dose to neoplasm delivered continuously but at lower dose rate)
- fractionation (same dose to neoplasm delivered in equal fractions separated by time)
*** biologic factors affecting radiosensitivity
- more sensitive in oxygenated state
- utero and old age most sensitive
- males more sensitive
- can recover if not killed before next division
- sulfhydryl groups are radioprotective
- vit K, methotrexate, actinomycin D are radiosensitizers
linear
nonlinear
response directly proportional to dose
response not directly proportional
threshold
nonthreshold
no response produced at a dose below the threshold dose
any size dose is expected to produce a response
direct v. indirect
interacts directly with a molecule like DNA
caused by free radicals formed from ionizing radiation interacting with body
*** estimated avg annual whole body dose of ionizing radiation from natural sources is…
300 mrem or 3 mSv
estimated avg annual whole body dose of ionizing radion from man-made sources is
630 mrem or 6.3mSv
cumulative annual dose for an adult is …
1/10 of age in yrs X 1 rem
ex: 40 yo — 4 rem or 4000 mrem
for pregnancy…
use high kVp technique and precise collimation of beam
entrance dose of foot xray =
less than 1 rad (1mGy)
[therapeutic abortion not indicated if fetal dose is less than 10 rad (10mGy)
effects of more than 10 rad radiation to fetus
2wks - spontaneous abortion or no effect
2nd-8th wk - congenital abnormalities of skeleton or nerves
2nd-3rd trimester - leukemia could occur in childhood
define dose limit
amount of radiation that if received annually runs the risk of death to 1 in 10,000
cumulative annual whole body occupational exposure
age (yrs) x 1 rem
*** Limits for occupationally exposed to radiation
annual effective =
cumulative annual effective =
equivalen annual dose fo rskin, hands, feet =
equivalent annual dose for lens of eye =
pregnant =
50 mSv or 5 rem
10 mSv or 1 rem x age
500 mSv
150 mSv or 15 rem
5 mSv (.5 rem for the 9 mo of preggers)
limit for children less than 18
1 mSv (100 mrem) for annual exposure
limits for adult public
1/10- that of radiation workers
typical exposure rate at the xray beam entrance into pt with fluoroscopy
2R/min
limit is 10R/min (why 5 min bell)
an operator position 3 ft from the xray beam entrance area will receive ___ of the pts ESE
0.1%
standing one step further away from the pt can cut the physician’s exposure rate by a factor of 4
dose rates reduced by factor of 5 when physician stands on image recepotr side of table during a lateral projection
who is required to wear lead aprons?
everyone in room or w/i 2 m if using a mobile c-arm
