SU-E-T-435: Comparison in Dose Distributions Between 2D-Arrays for Pre-Treatment IMRT QA

Purpose: In recent years, many 2D‐arrays have been developed as dose verification. Therefore, the comparison in the dose accuracy between the 2D‐arrays is important especially for complex intensity modulated radiation therapy(IMRT). In this study, we compared dosimetric properties between various 2D‐arrays and also evaluated the accuracy of absolute dose and dose profile measurements for clinical IMRT fields. Methods: In this study, the following detectors were used to check the dose accuracy: MapCHECK (Sun Nuclear, Melbourne, FL), EPID (Varian MedicalSystems, Palo Alto, CA), EPID‐based dosimetry (EPIDose, Sun Nuclear, Melbourne, FL), COMPASS (IBA Dosimetry, Germany) and EDR2 film (Eastman Kodak, Rochester, NY), Exradin A‐14SL ion chamber (0.016 cc, Standard Imaging, Middleton, WI). First the dosimetric properties of the 2D‐arrays were compared with dose linearity, dose rate, and output factor for 6 and 15 MV photon beams. Next the accuracy of the absolute dose and dose profile was evaluated for 21 clinical IMRT fields. Results: All detector responses for the dose linear were within 1%, and for the dose rates agreed within a standard deviation of ±1.2%. Except for EPID, the output factors were insignificant deviation. This is because EPID is the fluence measurement. In almost 2D‐arrays, the point dose agreed with treatment planningsystem (TPS) in less than 3% in the clinical fields. As for EPID, the accuracy that is equal to other detectors is obtained by some correction factors. Pass rates of each detector for TPS were more than 95% in the gamma analysis (criteria: 3 mm/3%). EPIDose is in a good agreement with TPS. This is because EPIDose has high resolution. Conclusions: All 2D arrays used in this study showed almost the same accuracy for clinical IMRT fields. EPIDose has better resolution than other 2D arrays and thus is expected for dose distributions with a small field.