ABR Quality Assurance and Quality Control 1 — Questions and Answers
Question 1: According to AAPM TG-142, what is the daily output constancy tolerance for a linear accelerator used for non-IMRT treatments?
- ±1%
- ±2% (Correct answer)
- ±3%
- ±5%
Correct answer: ±2%
TG-142 specifies a ±2% daily output constancy tolerance for conventional (non-IMRT) linac treatments.
Question 2: Which AAPM task group report provides the primary framework for absolute dose calibration of high-energy photon and electron beams in the United States?
- TG-51 (Correct answer)
- TG-142
- TG-119
- TG-218
Correct answer: TG-51
AAPM TG-51 is the standard protocol for absorbed-dose calibration of photon and electron beams using ionization chambers in a water phantom.
Question 3: The Winston-Lutz test is primarily used to verify which parameter of a linear accelerator?
- Beam flatness and symmetry
- Isocenter coincidence of radiation and mechanical axes (Correct answer)
- MLC leaf transmission
- Output linearity at low monitor units
Correct answer: Isocenter coincidence of radiation and mechanical axes
The Winston-Lutz test verifies that the radiation isocenter coincides with the mechanical isocenter by imaging a small ball bearing at multiple gantry, collimator, and couch angles.
Question 4: According to TG-142, what is the recommended tolerance for gantry angle accuracy on a linac?
- 0.1°
- 0.5° (Correct answer)
- 1.0°
- 2.0°
Correct answer: 0.5°
TG-142 recommends a ±0.5° tolerance for gantry angle accuracy under monthly QA testing.
Question 5: What is the standard source-to-surface distance (SSD) reference condition used for linac output calibration per TG-51?
- 80 cm SSD, 10×10 cm² field, dmax depth
- 100 cm SSD, 10×10 cm² field, 10 cm depth (Correct answer)
- 100 cm SSD, 10×10 cm² field, dmax depth
- 100 cm SAD, 10×10 cm² field, 5 cm depth
Correct answer: 100 cm SSD, 10×10 cm² field, 10 cm depth
TG-51 calibration is performed at 100 cm SSD, a 10×10 cm² field size, and a reference depth of 10 cm in a water phantom.
Question 6: Which QA procedure is specifically designed to test the end-to-end accuracy of a stereotactic radiosurgery (SRS) system?
- Winston-Lutz test
- End-to-End (E2E) test (Correct answer)
- Gamma knife Leksell frame check
- Output factor measurement
Correct answer: End-to-End (E2E) test
The End-to-End test simulates the full SRS workflow—imaging, planning, and delivery—to a phantom to verify the entire process achieves submillimeter accuracy.
Question 7: According to TG-142, what is the recommended monthly tolerance for beam flatness (non-IMRT) on a linear accelerator?
- ±0.5%
- ±1%
- ±2% (Correct answer)
- ±3%
Correct answer: ±2%
TG-142 specifies a ±2% monthly tolerance for beam flatness for conventional (non-IMRT) photon beams.
ABR Quality Assurance and Quality Control 1
According to AAPM TG-142, what is the daily output constancy tolerance for a linear accelerator used for non-IMRT treatments?