Study On The Optimal Threshold Of Gamma Passing Rate Based On Three-dimensional Dose Verification Under Different QA Tools

Gamma analysis as a common method for judging whether radiotherapy plan can be passed at present,However,the common thresholds of gamma passing rate does not necessarily make an accurate assessment of whether or not the radiotherapy plan is passed.Therefore,this study is based on the Delta 4 and EDose three-dimensional dose verification system to found the optimal gamma passing rate thresholds for different measurement methods(global and local)and different measurement benchmarks(3%/3mm,2%/2mm).A retrospective randomized selection of 15 IMRT plans of lung and esophageal cancer and 15 VMAT plans of nasopharyngeal carcinoma(NPC)and rectal cancers in Xiang Ya hospital from 2016-2017,the gamma analysis and DVH evaluation using by Delta 4 and Edose respectively.If the plans' absolute percentage dose errors of all specific dosimetry indices on the DVH is less than 5%,it is regarded as a clinically acceptable plan,otherwise it is considered as a clinically unacceptable plan.According to this standard,all the plans were classified and combined with gamma passing rate to found the optimal gamma passing rate threshold by used the ROC curve.Finally,the sensitivity and specificity were used to quantitatively compare the common thresholds and the optimal thresholds to identify false negative and false positive.Rectal cancer VMAT plans the optimal thresholds of 98.75% and 88.95% under the 3%/3mm and 2%/2mm measurement benchmarks by used global measurement method.The optimal thresholds under the same measurement benchmarks was 98.15% and 82.55% in the local measurement method.NPC VMAT plans the optimal thresholds of 99.35% and 95.40% under the 3%/3mm and 2%/2mm measurement benchmarks by used global measurement method.The optimal thresholds under the same measurement benchmarks was 98.25% and 94.05% in the local measurement method.Lung cancer IMRT plans the optimal thresholds of 97.37% and 88.39% under the 3%/3mm and 2%/2mm measurement benchmarks by used global measurement method.Esophageal cancer IMRT plans the optimal thresholds of 98.08% and 89.38%under the 3%/3mm and 2%/2mm measurement benchmarks by used global measurement method.The sensitivity of the optimal thresholds at the 3%/3mm benchmark is very good compared to the commonly thresholds.Using the 2%/2mm benchmark,the optimal thresholds was closer to the sensitivity and specificity and the two were more balanced compared to the 3%/3 mm benchmark.The application of this method can not only improve the clinical significance of patient specific quality assurance,but also provide the basis for the selection of gamma passing rate thresholds in plans verification for other hospitals and institutions,and provide a reference for the future exploration of more scientific and effective new measurement methods.