Patient delivery quality assurance for linac-based IMRT and helical tomotherapy using solid state detectors

The purpose of this study is to demonstrate how to perform and define appropriate action levels for the intensity-modulated radiation therapy (IMRT) delivery quality assurance (DQA) for both linear accelerator (linac) and helical tomotherapy (HT) plans using a 2D array diode detector. MapCHECK (Sun Nuclear, Melbourne, FL, USA) was used to perform the DQA measurements of patient plans at various sites: brain, head and neck, chest, abdomen, pelvis, spine, bone and others. The measured and planned doses were compared using gamma analysis with a total dose discrepancy of 3% or a gradient difference of 3 mm criteria. DQAs for 507 HT and 380 linac-based IMRT plans were performed, and the mean diode percentage passing rates for 3%/3 mm criteria were 93.8% and 95.1% respectively. For HT delivery, 4.6% and 9.5% of the plans had the passing rates below 80% and 85%, while for linac-based IMRT, 7.4% of the plans had the passing rates lower than 90%. Applying confidence limit with multiplier of 1, action levels for passing rates of 87% and 90% are recommended for HT and IMRT plans respectively. ► Quality assurance was performed for 7–9 fields IMRT and helical tomotherapy plans. ► Confidence limit with multiplier of 1 was used to define the results action levels. ► For helical tomotherapy plans, the overall action level is recommended to be 87%. ► For IMRT linac plans, the recommended overall action level is 90%.