RESUMO
Objective To investigate the impact of four different collimator angle optimization techniques on the planning target volume (PTV) and organ at risk (OAR) during intensity-modulated radiotherapy (IMRT) for gastric cancer.Methods Ten patients with gastric cancer undergoing IMRT in Zhongnan Hospital of Wuhan University from 2015 to 2016 years were recruited in this study.All IMRT plans were designed by conventional five fields (330°,10°,45°,90°and 180°).In the Eclipse treatment planning system,four different collimator angle optimization techniques with consistent planning optimization parameters were employed to design the IMRT plan.Collimator angle optimization techniques included the following aspects.The collimator angle was set at 0 degree (CL0),collimator angle was set at 90 degree (CL90),Eclipse automatic collimator angle optimization (CLA) was adopted and collimator angle was set as the angle when the distance between X-Jaws and PTV (CLx) was the shortest.The dosimetric parameters mainly included the conformal index (CI) of PTV,the homogeneity index (HI),the mean dose (Mean),and the dosage of OAR.The treatment time (Time),monitor unit (MU),control point (CP),split field (SF) and conformal distance (Fx) were also considered.Results Regarding CL0 as the control,the CI,HI and Mean did not significantly differ among four collimator angle optimization techniques (all P＞0.05),whereas CLx could significantly increase the average dose of PTV in the target area (P＜0.05);CLx optimization reduced the liver (V30 reduction by 1.54％),left kidney (V12 decrease by 1.46％),right kidney and other OARs,whereas it slightly increased the maximum dose of the small intestine and spinal cord (＜1％).CLgo and CLA optimization elevated the dose of OAR in gastric cancer.Among four different collimator angle optimization techniques,CLx optimization reduced the MU (25.02％),CP (26.03％),Fx (20.27％) and SF (by 1.3separate fields on average) and treatment time (10.03％).CLgo and CLA optimization could decrease the MU,CP,Fx and SF.CL90 optimization had certain advantages in shortening the treatment time,whereas CLA optimization could prolong the treatment time by 5.04％.Conclusions During IMRT for gastric cancer,CL90,CLA and CLx collimator angle optimization techniques can obtain comparable dosimetry distribution to CL0 optimization technique,which can reduce the MU,decrease the radiation leakage,shorten the treatment time and improve treatment efficiency.
RESUMO
Objective To preliminarily verify the feasibility of utilizing TG119 report to commission the volumetric modulated arc therapy (VMAT) plans.Methods Based on the test cases mentioned in TG119 report,7-/9-field intensity-modulated radiation therapy (IMRT) and dual-arc VMAT plans were devised by using two types of beam energy (6 MV and 10 MV) in the Eclipse TPS system according to the requirement of this report.All the plans were verified using 0.125cc semiflex thimble ionization chamber,MatriXX and Delta 4,respectively.The final results were statistically compared with the results measured by multiple institutions in the TG119 report.Results The resuhs of both IMRT and VMAT plans met the requirement of the TG119 report.The discrepancy of point dose in the high/low dose region of VMAT plans using different photon beams was ranged from-2.55％ to 2.55％,and ± 1.85％ for the IMRT plans.The percentage of γ passing points (±3％/3 mm) for the IMRT plans using 6 MV and 10 MV photon beams was 99.38％ and 99.53％,99.32％ and 99.46％ for the VMAT plans.The γ passing rate of the compound field exceeded 98％.Conclusions The VMAT plans with 6 MV and 10 MV photon beams meet the requirement of the TG119 report.TG119 report provides certain guidance for establishing a benchmark for dosimetry verification of the VMAT plans.
