Per-beam, planar IMRT QA passing rates do not predict clinically relevant patient dose errors.

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Quality Assurance

Background:

• Intensity-Modulated Radiation Therapy (IMRT) is a sophisticated radiotherapy technique.
• IMRT Quality Assurance (QA) is crucial for ensuring accurate dose delivery.
• Conventional IMRT QA often relies on planar dose metrics like Gamma passing rates.

Purpose of the Study:

• To determine the statistical correlation between per-beam, planar IMRT QA passing rates and anatomy-based dose errors.
• To assess the predictive power of the Gamma passing rate per beam for per-patient IMRT QA.
• To evaluate the clinical relevance of common IMRT QA performance metrics.

Main Methods:

• Ninety-six unique data sets were generated using 24 clinical head and neck IMRT plans.
• Four types of dose errors were induced in IMRT plans delivered by Varian linear accelerators.
• Error-free plans served as simulated measurements for comparison with error-induced plans.

Main Results:

• Weak to moderate correlations (Pearson's r: -0.295 to 0.653) were found between Gamma passing rates and clinical dose metrics.
• High Gamma passing rates sometimes corresponded to significant anatomy-based dose errors (false negatives).
• Low Gamma passing rates did not consistently indicate large dose errors (false positives).

Conclusions:

• Conventional IMRT QA metrics, such as Gamma passing rates, exhibit a lack of correlation with actual dose errors in critical anatomic regions.
• Current acceptance criteria and action levels for IMRT QA may have insufficient or unproven predictive power for per-patient accuracy.
• The findings suggest a need for more robust and clinically relevant IMRT QA methods to ensure treatment efficacy and patient safety.