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Quality Assurance and Quality Control Flashcards

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  1. The gamma (γ) index used in IMRT patient-specific QA combines which two criteria?

    Answer: Dose difference and distance-to-agreement

    The gamma index simultaneously evaluates dose difference (DD) and distance-to-agreement (DTA) to provide a single pass/fail metric for IMRT QA comparisons.

  2. AAPM TG-119 was developed primarily to establish:

    Answer: Commissioning benchmarks and test cases for IMRT planning and delivery

    TG-119 provides IMRT commissioning test cases with known dose distributions to help institutions benchmark their IMRT planning and delivery systems.

  3. Which AAPM report provides QA guidelines specifically for CT simulators used in radiation therapy?

    Answer: TG-66

    AAPM TG-66 addresses the quality assurance of CT simulators and establishes acceptance testing and periodic QA procedures for these devices.

  4. An EPID (Electronic Portal Imaging Device) is most commonly used in linac QA for:

    Answer: Patient position verification and transit dosimetry

    EPIDs are primarily used for patient setup verification via portal imaging and for transit dosimetry to detect delivery errors during or after treatment.

  5. What is the recommended passing criteria (gamma pass rate) for patient-specific IMRT QA according to AAPM TG-218?

    Answer: 95% of points with γ(3%/3mm) ≤1

    TG-218 recommends a universal tolerance of ≥95% passing rate using 3%/3 mm criteria with a 10% dose threshold for IMRT patient-specific QA.

  6. Machine-Specific Reference Fields (MSRF) are used in small-field dosimetry primarily because:

    Answer: Standard 10×10 cm² fields cannot be produced by some small-field devices like CyberKnife or MRI-linacs

    Some specialized machines (CyberKnife, Gamma Knife, MRI-linacs) cannot produce a 10×10 cm² reference field, so an MSRF of the largest available field is used as the reference instead.

  7. Which detector type is generally preferred for small-field dosimetry (fields < 3×3 cm²) due to its small sensitive volume and minimal perturbation?

    Answer: Diode or diamond detector

    Diode and diamond detectors have very small sensitive volumes (~1 mm³), making them well-suited for small-field dosimetry where volume-averaging effects with large chambers cause errors.