CAMRT Radiation Protection and Safety Questions and Answers 2 — Questions and Answers
Question 1: According to CNSC regulations, what is the annual effective dose limit for radiation workers?
- 10 mSv
- 20 mSv
- 50 mSv (Correct answer)
- 100 mSv
Correct answer: 50 mSv
The annual limit is 50 mSv with a 5-year cumulative limit of 100 mSv.
Lens of eye: 150 mSv/year. Extremities: 500 mSv/year. General public: 1 mSv/year. ALARA requires doses well below these limits.
Question 2: What is the inverse square law in radiation protection?
- Intensity doubles when distance halves
- Intensity decreases with the square of distance; doubling distance reduces exposure to one-quarter (Correct answer)
- Intensity decreases linearly with distance
- Only applies to radioactive sources
Correct answer: Intensity decreases with the square of distance; doubling distance reduces exposure to one-quarter
Doubling the distance reduces exposure to 25%.
Standing 2m vs 1m away reduces exposure to 25%. Operators must stand at least 2m from portable X-ray tubes. This is the cornerstone of practical radiation protection.
Question 3: A dosimeter was left on a sunlit windowsill over the weekend. What should the technologist do?
- Continue using it
- Report to the RSO, request replacement, note the incident for dose records (Correct answer)
- Discard without reporting
- Reset to zero
Correct answer: Report to the RSO, request replacement, note the incident for dose records
The incident must be reported so dose records can be annotated and a replacement issued.
The RSO will annotate the record and may estimate actual dose from comparison data. Never tamper with dosimeters. Readings are submitted to the National Dose Registry.
Question 4: What shielding material is most common for diagnostic X-ray protection?
- Concrete
- Lead, due to its high atomic number and density (Correct answer)
- Steel
- Copper
Correct answer: Lead, due to its high atomic number and density
Lead (Z=82) provides strong photoelectric absorption of diagnostic-energy photons.
0.5 mm lead attenuates 95-99% of scatter radiation. Lead garments must be inspected annually. Composite alternatives with barium, bismuth, or tungsten offer lighter weight.
Question 5: What is the purpose of the 10-day and 28-day rules for female patients?
- Specify maximum pregnancy dose
- Guide timing of non-urgent pelvic imaging to minimize irradiating an early pregnancy (Correct answer)
- Specify waiting periods before conception
- Define waiting periods between exams
Correct answer: Guide timing of non-urgent pelvic imaging to minimize irradiating an early pregnancy
These rules guide scheduling when pregnancy is least likely.
The 28-day rule considers pregnancy unlikely within 28 days of the last menstrual period. Rules apply only to non-urgent exams. Emergencies take priority.
Question 6: Which biological effects of radiation are most relevant in diagnostic imaging?
- Only deterministic effects
- Stochastic effects (cancer and hereditary) are primary, as diagnostic doses are below deterministic thresholds (Correct answer)
- Neither type at diagnostic levels
- Only acute radiation syndrome
Correct answer: Stochastic effects (cancer and hereditary) are primary, as diagnostic doses are below deterministic thresholds
Stochastic effects have no threshold, making any dose carry some probability of effect.
Stochastic effects increase in probability with dose. Deterministic effects have thresholds of hundreds of mGy, generally not reached in diagnostic imaging.
CAMRT Radiation Protection and Safety Questions and Answers 2
According to CNSC regulations, what is the annual effective dose limit for radiation workers?