A study to establish reasonable action limits for patient specific IMRT QA

Abstract

An effective patient quality assurance (QA) program for intensity modulated radiation therapy (IMRT) requires accurate and realistic plan acceptance criteria, i.e. action limits. The results of a routine patient QA program for IMRT plans, based on dose measurements performed with a commercially available 2D diode array, have been analyzed for 747 fluence maps. The fluence maps have been calculated by means of three different treatment planning systems (TPS) commercially available (ADAC, CMS, ECLIPSE) and delivered using 6 MV X-ray beams produced by linear accelerators. The agreement between the measured and calculated fluence maps was evaluated in terms of percent dose error (PDE) and percent of passing points (PPP), in order to establish reasonably achievable and clinically acceptable limits for the dose deviations. The analysis was conducted for each TPS (365 fluence maps ADAC, 220 Eclipse, 162 CMS) used in the study, for multiple treatment sites (prostate, pelvis, head and neck, spine, rectum, anus, lung, brain), at the optimum normalization point for a 3mm distance to agreement (DTA) and 3% dose error (%DE) criteria. The treatment site dependency of PPP and PDE was investigated. The results show that at the 3mm/3% criteria a 95% PPP and 3% PDE can be achieved for prostate treatments and a 90% PPP and 5% PDE is attainable for any treatment site.