Radiation Safety

Question 1

What is dose equivalence?

Answer 1

A means of quantifying biological effect of radiation dose, measured in Sieverts. Dependent on type of radiation and in some calculations organ at risk.

Question 2

List 4 agencies involved in the regulation of radionuclides in BC

Answer 2

1. Canadian Nuclear Safety Commission (CNSC):

Question 3

Describe the role of the Canadian Nuclear Safety Commission in radiation safety

Answer 3

Gives licenses stating what isotopes and devices can be possessed, and where or how they are to be handled. Includes brachy sources and Class II equipment (capable of creating radioisotopes), like LinAc with energy >= 10MV

Question 4

Describe the role of Health Canada in Radiation Safety

Answer 4

Regulates the design, construction, and performance of radiological x-ray equipment

Question 5

Describe the role of Transport Canada in radiation safety

Answer 5

i) Works with CNSC to provide regulations for the safe transport of radioactive materials with specific activity >74kBq/kg
ii) Provides certificate of training for persons involved in shipping radioactive materials

Question 6

Describe the role of the BC CDC in radiation safety

Answer 6

Provides leadership and expertise on radiation protection matters which fall under provincial jurisdiction, like facility design, QA, and protection

Question 7

List the personal monitoring limits per CNSC for:
i) Nuclear Energy worker (1 yr and 5yr)
ii) Pregnant NEW
iii) Non-NEW

Answer 7

i) 50mSv/yr, to max of 100 mSv/5 yrs
ii) 4 mSv in balance of pregnancy (monitored q2wkly)
iii) 1 mSv/yr

Question 8

Define TLD and how it works

Answer 8

TLD - Thermoluminescent dosimeter (think heat causing light!);
Works as radiation interacts with material (usually LiF or CaF) in solid crystal structure. Radiation will cause ionization reactions, and free electrons become trapped in crystal lattice. When heated, crystal will vibrate and allow electrons to return to ground state, emitting characteristic light, which can be measured and equated to RT exposure.
If left too long, electrons will naturally return to ground state so have to repeat semi-frequently.

Question 9

What is the yearly dose limit to the hand for:
i) NEW
ii) non-NEW

Answer 9

i) 500 mSv/year
ii) 50 mSv/year

Question 10

List 3 philosophies of radiation protection

Answer 10

i) Justification: all uses of radiation should be justified to ensure net benefit outweighs risks
ii) Optimization (aka ALARA): Keep effective dose to persons as low as is reasonably achieveable, when accounting for social and economic factors
iii) Regulatory limits: If applying the above two, regulatory limits should not be a factor

Question 11

For the general public, list sources of radiation exposure in order of total amount contributed

Answer 11

1. Radon (55%)
2. Internal (11%)
3. Medical x-rays (11%)
4. Cosmic (8%)
5. Terrestrial (8%)
6. Nuclear Medicine (4%)
7. Consumer products (3%)

Question 12

Describe the radioactive process of radon

Answer 12

Radon (Rn) is a noble gas and natural decay product of uranium and radium (half life on order of billions of years). It is the second most common cause of lung cancer!
Most commonly found as Rn-222, with half life-3.8 days.
Odorless gas which is easily inhaled, so able to deposit dose within the human body while decaying.
Rn-222 undergoes alpha decay to Po-218, so is very potent at dose deposition within the lungs, too.
Multiple further decays before finally finishing as stable Pb-206

Question 13

List common medical scan in order of radiation exposure, from least to most

Answer 13

1. Bone density scan aka DEXA (0.0002-0.001 mSv depending on source)
2. Extremity x-ray (0.001mSv)
3. Dental Panorex (0.025 mSv)
4. CXR (0.05 mSv per view)
5. Mammography (1 mSv)
6. Low Dose Lung CT for screening (1.5 mSv)
7. Pelvis X-ray/Lumbar spine Xray (1.6 mSv)
8. Head CT (2 mSv)
9. Chest CT (7 mSv)
10. Abdomen CT (10 mSv)
11. Whole Body CT (15 mSv)
12. PET (22.7 mSv)

Question 14

What is average Canadian background radiation dose?

Answer 14

2-3 mSv/yr (closer to 1 in Vancouver and 4 in Winnipeg)

Question 15

List 5 ways to quantify risk

Answer 15

i) Background risk: Overall risk of “unexposed population”
ii) Excess absolute risk: Additional risk that RT adds to background
iii) Relative risk: Ratio of risk for exposed persons to risk for unexposed
iv) Excess relative risk: Relative risk - 1.0
v) Total lifetime risk: Relative risk x absolute lifetime background risk

Question 16

What are the two types of health risks associated with RT exposure:

Answer 16

i) Deterministic - dose-dependent risks with predicatable severity and thresholds (like acute tox)
ii) Stochastic - dose-independent, but probabilistic, without threshold (like second malignancy)

Question 17

What are the four phases of acute radiation syndrome

Answer 17

i) Prodromal period (within minutes to days from exposure, may last episodically for minutes to days)
ii) Latent period where patient appears healthy (not always present, a few hours to a few weeks)
iii) Period of manifest illness (depend on specific syndrome, last hours to months)
iv) Recovery (death within several months, or recovery over several weeks to two years)

Question 18

What are the classic symptoms of prodromal stage of acute radiation syndrome?

Answer 18

i) Nausea
ii) Vomiting
iii) anorexia
iv) diarrhea depending on dose
May be episodic

Question 19

List three classic acute radiation syndrome sub-syndromes

Answer 19

i) Bone marrow (hematopoietic) syndrome: Doses between 0.7 and 10 Gy - at higher doses leads to death through infection and hemorrhage
ii) GI syndrome: Doses greater than 10 Gy for full syndrome - Usually leads to death within 2 weeks (survival rare) due to above syndrome + dehydration and electrolyte imbalance
iii) CV + CNS syndrome: Doses above 50Gy. Usually leads to death within 3 days (recovery is NOT seen)

Question 20

List three organ specific deterministic effects

Answer 20

i) Cutaneous radiation syndrome (inflammation, erythema, desquamation, ulceration/necrosis)
ii) Cataracts (>2-3 Sv)
iii) Sterility: Temporary (0.15-3.5 Sv) or permanent (>3.5-6 Sv)
In general, more severe in cells with higher proliferation rate and lower degree of differentiation

Question 21

What is the LD50/60 defined as?

Answer 21

LD50/60 = dose necessary to kill 50% of exposed population at 60 days
Most estimates place LD50/60 at 2.5-5 Gy)

Question 22

List the deterministic RT effects per stage of embryonal development

Answer 22

i) Preimplantation phase (0-10 days post-conception): death
ii) Organogenesis phase (2-10 weeks): anencephaly, mental retardation, microcephaly (threshold 1-50 cSv)
iii) Fetal stage (8-38 weeks): mental retardation (above 100-700 mGy), microcephaly above 500 mSv

Question 23

List two types of stochastic RT effects, depending on cell line

Answer 23

i) Carcinogenesis in somatic cells –> seen after long latent periods of 2-40 years
ii) Mutagenesis in germ cells, seen in subsequent generations

Question 24

What dose is needed to double spontaneous mutation rate?

Answer 24

1 Sv

Question 25

What are 5 most common radiation induced malignancies, and which has shortest latency period?

Answer 25

Breast, thyroid, lung, leukemia, alimentary tract

Shortest is leukemia at ~10 years!

Question 26

List shielding requirements for a linac vault

Answer 26

a) Treatment unit shielding (primary collimator, beam stopper if room shielding poor)
b) Room shielding, usually made of concrete
i) Primary barrier (thickest) which will be wherever primary RT can strike
ii) Secondary barrier, outside primary and only shields against secondary rads (leakage, scatter)
iii) maze at room entrance to protect door from secondary radiation
iv) room door - usually also has shielding, dependent on maze

Question 27

What needs to be factored into shielding calculations?

Answer 27

i) Attenuation by chosen shielding material
ii) Inverse square effects
iii) Overall machine workload
iv) Use factors for various gantry angles
v) Occupancy of areas outside of vault

Question 28

How do we shield for neutrons produced with high energy linac beams?

Answer 28

i) Maze is most important!
ii) Also need proton-rich but low Z material like paraffin or hydrogen plastic on room door to attenuate neturons
iii) Door also needs high Z material, as above reaction will create gamma rays
iv) Concrete is fine everywhere else

Question 29

List three principles to minimize radiation exposure

Answer 29

i) Minimize TIME spent near source
ii) Maximize DISTANCE from source and avoid direct beam if collimated
iii) Place SHIELDING between yourself and source

Question 30

Any security precautions for RA material?

Answer 30

All RA material must be in a secure location, like a locked room

Question 31

What training or awareness is needed for staff?

Answer 31

i) Know purpose and location of emergency equipment
ii) Know emergency procedures
iii) Contact RSO once situation contained

Question 32

List 5 steps of basic emergency procedure

Answer 32

i) Press all emergency stop(s)
ii) Use a radiation detector when entering a room with a radiation source on or exposed
iii) Separate patient from radiation source
iv) clear room of patient and personnel, secure the room and post warning sign
v) Contact physics +/- RSO

Question 33

What signage is necessary for radiation safety?

Answer 33

i ) Warning signs on doors of all rooms with radiation sources
ii) Warning lights to indicate beam on/off
iii) Radiation warning signs posted outside room during live source brachy procedures
iv) Emergency contact information displayed at any location where radioactive material is stored

Question 34

List responsibilities of radiation safety officer

Answer 34

Per CNSC, broadly is to ensure all requirements are followed. Includes:
i) Ensuring the health and safety of personnel, the public, and environment
ii) Oversight of the daily aspects of the Radiation Protection Program
iii) Acting as the primary contact with the CNSC for licensing and compliance matters
iii) Identifying radiation safety problems
iv) Implenting corrective actions
v) Ensuring compliance with CNSC regulatory requirements
vi) Reporting regulatory non-compliances to the CNSC
vii) Holding the authority to stop any activity related to the operation of a class II facility that might result in non-compliance
viii) Developing procedures and policies related to radiation safety and training
ix) acting as the signing authority for CNSC licenses

Question 35

What organizations need to appoint an RSO

Answer 35

Any licensees under the CNSC who operate class II nuclear facilities of who service class II prescribed equipment