Radiation Protection

What is a stochastic effect?

• probability of occurrence increases with increasing absorbed dose, but severity of result doesn’t depend on size of dose

• ex: cancer

What is a non-stochastic effect?

• increases in severity with increasing absorbed dose in affected individuals

• ex: erythema

What does radiation protection assume about dose to risk relationships?

• that they are linear no threshold

• radiation has potential to cause harm at any dose level

What is the dose equivalent formula?

• effective dose equivalent = dose x quality factor

What is the tolerance dose for hematopoietic syndrome?

• 2-3 Gy to whole body

• months of survival

What is the tolerance dose for gastrointestinal syndrome?

• 5-12 Gy to whole body

• 1 week survival

What is the tolerance dose for CNS syndrome?

• more than 12 Gy to whole body

• 1 day of survival

what is the effective dose equivalent for background radiation in the US?

• 3mSv/year (300mrem/year)

What is the annual occupational exposure limit (stochastic effects)?

• effect dose-equivalent limit: 50 mSv or 5 rem

What is the annual occupational exposure limit to the lens of the eye (non stochastic)?

• 150 mSv

• 15 rem

What is the annual occupational exposure limit to the extremities?

• 500 mSv

• 50 rem

What is the annual occupational cumulative exposure limit?

• 10 mSv x age in years

• 1 rem x age in years

What are the annual public exposure limits for continuous or frequent exposure?

• 1 mSv or 0.1 rem

What is the annual public exposure limit for infrequent exposure?

• 5 mSv

• 0.5 rem

What are the education and training annual exposure limits?

• effective dose equivalent: 1mSv or 0.1 rem

• dose-equivalent limit for lens, skin, extremities: 50 mSv or 5 rem

what are the embryo-fetus exposure limits?

• total: 5mSv or 0.5 rem

• monthly: 0.5 mSv or 0.05 rem

• negligible:0.01

what is the LD 50/60?

• dose to which 50% of those exposed would die within 60 days

• 3-4 Gy to whole body

what information do film badges tell us about the beam?

• beam quality

• we can estimate penetration ability of the radiation

what does a pocket dosimeter do?

provides a quicker exposure measurement than a film badge

What does the NRC (nuclear regulatory commission) control?

• the use of reactor-produced materials

• agreement states follow their rules (states don’t have to be agreement)

What are NRC rules?

• ALARA

• RSO

• Radiation saftey committee

• written directive verifying patient, rx, and source for brachy procedures

what is a medical event?

• wrong patient

• total dose delivered differs from prescribed dose by 20% or more

• fractionated differs by 50% or more

What are the dose limits in a controlled area?

• only radiation workers can access

• <0.1 mSv/week

What are the dose limits in a non-controlled area?

• <0.02 mSv/week

What is the workload factor?

• weekly dose delivered at 1m from the source

What is the use factor?

• fraction of operating time that radiation is pointed toward a barrier

what is the occupancy factor?

• fraction of operating time during which an area is occupied by an individual

what is the shielding formula?

• workload x use factor x occupancy / d²

when does neutron contamination need to be considered?

• for accelerators operating at 10MV or more

why is lead a bad neutron shield?

• would produce more neutrons in high energy MV beams

• borated polyethlene (plastic) is best

what needs more shielding, IMRT or 3D plans?

• IMRT bc more leakage bc more MUs