The lack of correlation between conventional IMRT QA performance metrics gamma passing rates and dose errors in DVHs values and the low sensitivity of 3%∕3 mm global gamma method show that the most common published acceptance criteria have disputable predictive power for per-patient IMRT QA.

The variability of %GP obtained confirmed the necessity to establish defined agreement criteria that could be universal and comparable between institutions. In particular, while the gamma passing rate does not depend on the choice of threshold, the choice of DDT strongly influences the gamma passing rate for local calculations. The difference between global and local %GP was statistically significant for prostate and other treatment sites when DDT was changed from 2 to 3 cGy.

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