ARRT Radiation Safety 2 — Questions and Answers
Question 1: Which radiation weighting factor (wR) applies to X-rays used in CT imaging?
- 1 (Correct answer)
- 2
- 5
- 20
Correct answer: 1
X-rays and gamma rays have a radiation weighting factor of 1, meaning 1 Gy equals 1 Sv.
Question 2: What is the primary purpose of the CT dose index (CTDI)?
- To measure patient absorbed dose in a single organ
- To characterize radiation output of a CT scanner independent of patient size (Correct answer)
- To calculate the effective dose to the technologist
- To determine scatter radiation levels in the control room
Correct answer: To characterize radiation output of a CT scanner independent of patient size
CTDI characterizes the radiation output of a CT scanner and allows standardized comparison between scanners and protocols.
Question 3: A patient weighing 300 lbs is scanned using a standard adult protocol. How should the technologist respond?
- Use pediatric technique factors
- Reduce mAs by 50% regardless of image quality
- Apply size-specific dose estimates (SSDE) and adjust technique for body habitus (Correct answer)
- Increase kVp to 140 and decrease mAs proportionally
Correct answer: Apply size-specific dose estimates (SSDE) and adjust technique for body habitus
SSDE accounts for patient size and provides a more accurate dose estimate; technique should be adjusted to match body habitus while maintaining diagnostic quality.
Question 4: Which of the following best describes the ALARA principle in CT imaging?
- Use the lowest dose that produces any visible image
- Keep radiation exposure as low as reasonably achievable while maintaining diagnostic image quality (Correct answer)
- Always use the minimum protocol mAs regardless of indication
- Limit CT exams to one per patient per year
Correct answer: Keep radiation exposure as low as reasonably achievable while maintaining diagnostic image quality
ALARA means optimizing dose to the lowest level that still yields diagnostically acceptable images for the clinical indication.
Question 5: The dose length product (DLP) is calculated by multiplying CTDI_vol by which parameter?
- Pitch factor
- Scan length (cm) (Correct answer)
- Rotation time
- Number of detector rows
Correct answer: Scan length (cm)
DLP = CTDI_vol × scan length (cm), providing a single value that reflects the total radiation energy deposited during the scan.
Question 6: Which type of shielding is most effective for reducing scattered X-ray radiation outside a CT suite?
- Aluminum sheeting
- Lead-lined walls or concrete barriers (Correct answer)
- Acrylic barriers
- Wooden partitions with lead paint
Correct answer: Lead-lined walls or concrete barriers
Lead-lined walls and concrete barriers are the standard structural shielding materials used to attenuate scattered radiation from CT suites.
Question 7: A CT technologist is concerned about cumulative occupational dose. Which dosimeter provides the most accurate record of whole-body exposure?
- Finger ring TLD
- Pocket ionization chamber
- Optically stimulated luminescence (OSL) badge worn at collar level (Correct answer)
- Electronic personal dosimeter worn at waist
Correct answer: Optically stimulated luminescence (OSL) badge worn at collar level
An OSL badge worn at the collar (outside any lead apron) is the standard for whole-body occupational dose monitoring and provides accurate cumulative records.
ARRT Radiation Safety 2
Which radiation weighting factor (wR) applies to X-rays used in CT imaging?