SU‐E‐T‐459: Measurement of Gated Rapidarc Accuracy

Abstract

Purpose: Recently, Kyung Hee university hospital at Gangdong installed the Varian 21iX linac which has the volumetric imrt (RapidArc) option and a real‐time position management (RPM) system. One of advantage of rapidarc is a short treatment time comparing with other treatments. Thus, the rapidarc treatment with the RPM system for the lung and liver cases, can reduce the treatment time comparing with the intensity modulation radiotherapy (IMRT) and 3 dimensional radiotherapy (3DRT) with gating system. Therefore, we estimate the accuracy of the gated rapidarc treatment. Methods: 10 patients data are used for this study. Each patient was planned by rapidarc technique using varian ECLISPE v8.6 planning machine. For the patient Quality Assurence (QA), a MATRIXX detector and IˈM RT software are used. At bottom and top of MATRIXX detector, 5×30×30cm̂3 of solid water phantoms are install for build up. A MATRIXX detector is fixed but the infrared reflecting box is periodically moved to provide the gating signal to the RPM system. Each patients dosimetric distribution is measured and the treatment summary which is provided by linac operating system is recoded to estimate the accuracy of the gated rapidarc treatment. Results: The dosimetric comparison between the measurement and the treatment plan is matched well for the 10 patients. With 3% of delta dose and 3mm of delta distance, more than 98% of area gives the gamma value as less than 1. Conclusions: We found that the patient dose measurement is matched well with the RTP planˈs dose distribution for the gated rapidarc treatment cases in the mechanical point of view. This study shows the gated rapidarcˈs dose reproducibility during the patient QA but this result has a limitation for the dose confirming for the real patients which has more soft and flexible body than the solid phantom.