Incorporation of geometrical information on structure position to gamma analysis results for portal dosimetry based IMRT prostate verification

Abstract

Introduction Gamma analysis became a standard tool to evaluate the agreement between planned and delivered fluence/dose distribution. The importance of points out of tolerance limit is always the same, because the analysis does not include any information on position of relevant structures for the current Beam’s eye view (BEV). We have suggested the method for incorporation this into the gamma analysis result. Purpose The aim of this work was to create the application in Matlab software that would use the corrective matrix to be applied to the result matrix of gamma analysis from portal dosimetry with EPID for each new prostate IMRT patient to warn about unacceptable results in the most critical areas. Materials and methods The results of gamma analysis for 30 prostate patients were analyzed. Patients were treated with 5 fields sliding window IMRT on Clinac DHX. Gamma map has been matched with BEV projection of PTV, rectum, and bladder for current patient. The sum matrix of BEV over all patients for each gantry angle was created to show the most frequent BEV localization of current structure. The weighting matrix was created to be applied to the gamma analysis results of prostate IMRT increasing the importance of unsatisfactory results at areas where projections of organs are most probable. Results and conclusion The weighting matrix is the result of optimization process which took into account frequent position of BEVs and frequent position of pixels out of tolerance within gamma analysis. Disclosure Authors have no potential conflict of interest to disclose.