Practice Test Geeks(CMD) Certified Medical Dosimetrist Practice Test
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Quality Assurance & Control Flashcards

7 cards from real CMD practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 Quality Assurance & Control flashcards as text

  1. Which TG-51 measurement condition requires the use of a plastic water phantom for electron beam calibration?

    Answer: When measuring beams with energy below 6 MeV where polarity correction is significant

    For low-energy electron beams (below ~6 MeV), polarity corrections become significant and the TG-51 protocol provides additional guidance for handling these measurements.

  2. A daily QA check reveals the radiation isocenter and mechanical isocenter are offset by 2.5 mm. According to TG-142, what action is appropriate?

    Answer: Suspend treatments and investigate immediately

    TG-142 specifies that the radiation isocenter coincidence with mechanical isocenter should be within 2 mm; a 2.5 mm offset exceeds tolerance and requires immediate investigation.

  3. What is the primary purpose of performing a Winston-Lutz test on a stereotactic radiosurgery system?

    Answer: Checking the coincidence of radiation and mechanical isocenters

    The Winston-Lutz test verifies that the radiation beam passes through the mechanical isocenter during gantry, collimator, and couch rotation, ensuring SRS geometric accuracy.

  4. During monthly QA, the output of a 6 MV beam measures 0.97 Gy for a prescribed 1.00 Gy delivery. What is the percentage deviation and is it within TG-142 monthly tolerance?

    Answer: 3% deviation; outside monthly tolerance of 2%

    A 3% deviation exceeds the TG-142 monthly output tolerance of 2% for photon beams, requiring investigation and potential recalibration.

  5. Which detector is most appropriate for measuring output factors in small radiation fields (less than 2×2 cm) used in SRS?

    Answer: Radiochromic film or small diode detector

    Small fields require detectors with high spatial resolution such as radiochromic film, small diodes, or diamond detectors because standard ionization chambers over-average dose in the steep gradient regions.

  6. In a photon beam depth-dose measurement, the depth of maximum dose (dmax) shifts proximally when which parameter changes?

    Answer: Beam energy decreases

    Lower energy photon beams have shallower dmax depths; as beam energy decreases, dmax shifts toward the surface.

  7. A physicist notices that EPID-based daily output checks consistently read 1.5% higher than the ion chamber measurement. What is the MOST likely cause?

    Answer: The EPID gain calibration has drifted

    EPID response can drift over time due to dark current changes, panel aging, or calibration drift, causing systematic offsets relative to absolute dosimetry.