(Sunday, 7/14/2019)
Room: ePoster Forums
Purpose: The aim of this study was to generate a local confidence limit (CL) for IMR and VMAT techniques for Varian IX linear accelerator using the AAPM TG119 protocol.
Methods: We used TG119 cases to create plans for IMRT and VMAT in Eclipse Treatment Planning System for Varian IX using 6MV and 10MV photons. Verification plans were created in a planning slab phantom, 2D Matrix dosimetry system (I’mRT MatriXX) with multicube phantom and a volumetric phantom (Delta4). Radiation absorbtion doses to high dose points in the PTV region and low dose points in avoidance structures were measured with a 0.125cc semiflex thimble ionization chamber (PTW).The local confidence limits with the bench mark set by TG119 were obtained for point, planar and spatial measurements for IMRT and VMAT with different energies.
Results: In this study, the CLs for the high dose regions of IMRT with 6MV and 10MV were 0.025 and 0.014 respectively. For VMAT, they were 0.032 and 0.018. The counterpart CL was 0.045 in TG119. And in OARs region, the CLs of IMRT with 6MV and 10MV beam were 0.022 and 0.019 respectively with the counterpart CL indicated by TG 119 was 0.047. For VMAT with 6MV and 10MV photon beams, the CLs were measured 0.030 and 0.027 with Delta4 respectively. The CLs of the maximum Gamma Passing for all values were 2.0 in 6MV VMAT plan, which however recommended in TG119 was 12.4. The data presented here showed all the CLs in our clinic are well fit the TG119 report.
Conclusion: All these local CLs reached the goals mentioned in AAPM TG-119, which indicated that the local clinic had commissioned IMRT and VMAT techniques with adequate accuracy. Prior to the clinical application practice, The study allows us to better understand the basic capabilities of VMAT technology.
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