Poster — Wed Eve—29: Validation of VMAT Delivery Using a Commercial 2D Diode Array
Volumetric modulated arc therapy (VMAT) is a new modality that combines IMRT with rotational delivery. RapidArc (Varian Medical Systems) incorporates the capability to vary dose rate, gantry speed and dynamic multileaf collimators to optimize dose and delivery efficiency. While new systems are being developed for VMAT verification, diode arrays are efficient and convenient tools for beam‐wise verification of IMRTdelivery, and also have been employed in composite rotational delivery verification. Mapcheck2 (Sun Nuclear Corporation) is a new diode array with 1527 detectors. In this study, we investigate the use of Mapchekc2 in the MapPhan solid water phantom to validate VMAT delivery. 5 VMAT plans were generated in Eclipse using the RapidArc optimizer. All plans were delivered several times to verify consistency of delivery and measurement. Gamma analysis was used to verify the results compared to calculated dose distributions. The system was found to be sensitive to small changes in position or orientation. RapidArc beam delivery has been verified to correspond well with calculated dose distributions. Gamma values were below 1 in greater than 90% of measured points for all treatment plans. Delivery was found to be insensitive to initial dose rate. The MapPhan, with Mapcheck2 2D array in solidwater is a convenient way to verify VMAT plans. MapPhan results showed that RapidArc delivery is stable and reproducible.