Radiation Safety

Question 1

Permissible dose rate in an uncontrolled area

Answer 1

0.02 mSv in any 1 hour

Question 2

Permissible dose rate in a controlled area

Answer 2

1 mSv/h

Question 3

Dose limits for radiation workers

Answer 3

Stochastic:

• Annual: 50 mSv
• Cumulative: 10 mSv x Age

Deterministic:

• Lens: 150 mSv/yr
• Skin & Extremities: 500 mSv/yr

Minor workers: 10% of adult limit

Pregnant worker: 5 mSv over duration of pregnancy

Question 4

Dose limits for members of the public

Answer 4

Stochastic:

• Continuous exposure: 1 mSv
• Infrequent exposure: 5 mSv

Deterministic:
- Lens & Extremities: 50 mSv/yr

Embryo/Fetus:
- Equivalent dose limit: 0.5 mSv in a month once
pregnancy is known

Question 5

Basis for radiation dose limits

Answer 5

NCRP 116:

1. To prevent deterministic effects by limiting doses to below threshold levels
2. To limit the risk of stochastic effects to a reasonable level considering societal needs and benefits

Question 6

Agency that determines how dose limit recommendations will be implemented in the US?

Answer 6

National Council on Radiation Protection (NCRP)

Question 7

Agencies that develop exposure limits based on available data on radiation risk

Answer 7

1. United Nations Safety Committee on the Effects of Atomic Radiation (UNSCEAR)
2. International Commission on Radiation Protection (ICRP)
3. National Research Council Committee on the Biological Effects of Ionizing Radiation (BEIR)

Question 8

Why are dose limits higher for radiation workers?

Answer 8

Because they have received special training, are aware of the associated risks, and have decided to accept them.

Question 9

Radiation exposure risk report reference

Answer 9

BEIR VII Report

Question 10

Radiation risk model used by BEIR

Answer 10

Linear no-threshold (LNT)

Question 11

Radiation weighting factors for:

1. Photons/Electrons
2. Neutrons
3. Protons
4. Alphas

Answer 11

Photons/Electrons: 1
Neutrons: 2-11 (energy dependent), 10 (unknown energy)
Protons: 10
Alphas: 20

Question 12

Amount of annual natural background radiation

Answer 12

3 mSv

Question 13

Amount of annual exposure to radiation from medical uses

Answer 13

3 mSv

Question 14

Three types of release criteria for patients implanted/injected with radionuclides

Answer 14

From NRC NUREG-1556:

1) If activity administered is less than:
I-125 < 9 mCi
Pd-103 < 40 mCi
Ir-192 < 2 mCi

2) If dose Rate @ 1m from patient is less than:
I-125 < 0.01 mSv/h
Pd-103 < 0.008 mSv/h
Ir-192 < 0.03 mSv/h

3) Patient-specific calculation ensures that no individual will receive more than 5 mSv

Question 15

When should a patient injected/implanted with RAM be given instructions on how to maintain acceptable dose limits for others?

Answer 15

If the dose rate @ 1 m from the patient exceeds levels stated in NRC NUREG-1556 (usually within 20% of release criteria)

Question 16

Which personnel should have radiation monitoring performed?

Answer 16

Radiation workers who have a reasonable possibility of exceeding 10% of the annual limit

Question 17

Where should personal dosimeters be worn?

Answer 17

On the trunk of the body above the waist and on extremities when handling RAM

Question 18

Reference for linac shielding

Answer 18

NCRP 151

Question 19

Linac shielding equations

Answer 19

Barrier transmission factor: B = P^2/WUT
No. of TVLs: n = -log(B)
Thickness: X = TVL1 + (n-1)TVLe

Question 20

Energy and Intensity of leakage vs. primary vs. scattered radiation

Answer 20

Energy: Leakage > Primary&raquo_space; Scatter
Intensity: Primary > Scatter&raquo_space; Leakage

Question 21

Limit for linac head leakage

Answer 21

0.1% of primary beam @ 1m from the head

Question 22

High radiation area

Answer 22

Area in which radiation levels may be > 1 mSv in 1 hour @ 30 cm from the source

Question 23

Very high radiation area

Answer 23

Area in which radiation levels may be in > 5 Gy in 1 hour

@ 1 m from the source