Fall 2012 - Radiology - Test 1 - Rad Safety

Front 1

define radiation including the different categories of radiation

Back 1

radiation
- energy emitted and transferred through space

ionizing rad
- rad capable of displacing e- from atoms or molecules thereby producing ion pairs
- creates a free e- running around and a + charged atom

non-ionizing
- light, ultrasound, radio, MRI, cell phone

particulate
- forms of rad that have mass assoc with them
- e-, neutrons

non-particulate
- forms that have no mass assoc with them
- medical xrays (photons)

Front 2

what measurements are commonly used to monitor radiation exposure

Back 2

radiation exposure
- measure amt of ionization produced IN AIR by xrays and gamma rays
- unit = roentgen
- not applicable to particulate radiation (a particles, b particles, or neutrons)

radiation absorbed dose
- energy deposited by ionizing radiation IN MATTER
- SI unit - gray (1 Gy = 1 joule of energy per kig of tiss that is absorbing it)


radiation absorbed dose equivalent
- takes into consideration the variations in biologic damage caused by diff types of radiation
- rad dose equiv (Sv) = absorbed dose (gy) x weighting factor (wr)
- wr for xrays = 1
- wr for alpha particles = 20

Front 3

____ is the critical target for cellular injury by ionizing rad

Back 3

DNA

Front 4

contrast radiation exposure vs radiation absorbed dose vs radiation dose equivalent

Back 4

Front 5

Deterministic (non-stochastic) effects

vs

Stochastic effects

Back 5

Deterministic
- A dose threshold exists below which there is no effect
- Severity proportional to dose above threshold
- E.g.: cataracts, erythema, fibrosis, hematopoietic damage

Stochastic Effects
- Random effects
- Probability of effect proportional to dose
- Severity of effect not proportional to dose
- Think of skin cancer, you don’t know that at x hrs in the sun you will get cancer (it could occur at hr 1 or never, but the more exposure there is, the more likely you are to get a mutation) and the severity of the dz isn’t dependent on the number of hrs in the sun (it is depd on the type of mutation)
- examples: cancer induction, genetic mutation
- Implication is that there is no absolutely safe dose of radiation
- Basis of ALARA approach

Front 6

what is the major concern in a medical practice, acute or chronic radiation injury

Back 6

chronic

Front 7

regulations of max permissible dose levels are designed to limit (deterministic or stochastic) effects

Back 7

deterministic

can't design prev prog for stochastic effects b/c they are random/ not predictable

Front 8

MPD
for occupational worker vs general public

lifetime max accumulated dose for occupational worker

Back 8

occupational worker
- annual limit = 5000 mrem/yr
- aka 5 rem, 50 mSv

gen public
- 500 mRem/yr
- 10% of occupational dose

Lifetime MAD
- MAD = age in yrs x 1 rem

Front 9

occupational workers and preg

Back 9

preg declaration - voluntary

instution/ employer is required to maintain radiation exposure to fetus at < 500 mrem during gestation

fetal exposure must be reported (fetus gets dosimeter)

Front 10

radiation effects in utero

Back 10

depd on dose, dose rate, stage of fetal development at time of exposure

pre-implantation
- day 0-9
- time b/w fertilization and attachment of embryo to uterine wall
- MOST SENSITIVE TO LETHAL EFFECTS OF RADIATION
- embryo dies or repairs damage (all or nothing)

organogenesis
- 10 d - 6 wk
- congenital malformations/ most severe intrauterine growth retardation
- if death does occur, it is usually neonatal

fetal growth stage
- 6 wk - term
- growth of previously formed organs
- PEAK SENSITIVITY 8-15 WKS
- radiation induced prenatal death and congenital abn is negligible
- usually CNS signs (behav probs, decreased IQ, perm growth retard, childhood cancers)

Front 11

what is ALARA

Back 11

as low as reasonably achievable

recognizes that benefits of using radiation justify some reasonable personnel exposure

radiation exposure to personnel should and can be limited to the min necessary to achieve benefits of radiation use

time
- minimize time of exp to rad

distance
- max dist from rad source
- inverse sq law (double dist = decrease exposure by factor of 4)

shielding
- personnel protection
- lead apron 0.25 - 1 mm
- lead gloves - 0.25 mm
- lead thyroid - 0.5 mm
- LEAD SHIELDING ONLY PROTECTS AGAINST SCATTER RADIATION
- beam filtration (attaches to collimator in primary beam, removes low energy photons that have no dx value)
- beam limiting devices (collimation)

record keeping
- TN state law req that log kept of persons holding an animal or cassette during exp (includes date, name of procedure, name of person)
- helpful if worker receives high dosimetry report