Error detection sensitivity test using complex errors on three patient-specific VMAT QA systems

Abstract

The purpose of this study was to investigate error detection sensitivity for three patient-specific volumetric modulated arc therapy (VMAT) quality assurance (QA) systems (Delta4, EPID-based dosimetry, and log file) with three possible scenarios. Ten patient-specific VMAT QA were randomly selected to test their error detection sensitivities. Artificial complex errors were introduced to the original plans then the QA tests were repeated. These errors were simulated into three possible scenarios: uncertainty, miss-calibration, and worst-case scenario. For uncertainty scenario, the random errors (σ) of multi-leaf collimators (MLC) at ± 2.0 mm and gantry angle at ± 2.0 degree were introduced. The systematic errors of +2MU, and the random errors of MLC and gantry angle at ± 2.0 mm and ± 2.0 degree were applied as a miss-calibration scenario. For worst case scenario, errors were integrated between systematic and random variation of MLC and gantry angle at 2±0.5 mm and 2±0.5 degree, respectively. The dosimetric agreements between QA tests on original versus artificial error plans were determined to investigate error detection sensitivity used gamma analysis with 3%, 3 mm criteria. EPID-based dosimetry showed the most sensitive QA tool to detect three possible scenarios. Log file was the second best method, whereas Delta4 was the worst method to detect three possible scenario errors.