SU-E-T-643: A Comparison of the DTA and Gamma Index Analysis for IMRT/VMAT Plans in Rectal Carcinoma

Abstract

Purpose: To investigate the variability of the global gamma index analysis for IMRT and VMAT plans in Rectal Carcinoma, assess the impact of criterion by 3mm/3% or 4mm/4% gamma index and DTA method. Methods: In ten patients, five‐field IMRT plans with fixed gantry positions were compared to two dual arcs VMAT plans, each of them was optimized with Oncentra4.3 planning system, and designed by experienced planners using appropriate similar optimization parameters and dose constraints with a number of iterations to meet the clinical acceptance criteria. Plans were normalized so that at least 95% of PTV would receive the prescription dose 50 Gray in 25 fractions. Measurements of the plan dose distribution were performed and analyzed with Delta4 detector array by 3mm/3% or 4mm/4% gamma index and DTA methods. Results: All plans passed in the dose verification, for gamma criterion, an average of 93.13% of the detector points passed the 3 mm/3% for VMAT plans while in IMRT verification it was 96% (p=0.017), the lowest pass‐rate were 90.2% for VMAT and 91.2% for IMRT; For 4 mm/4% gamma criterion, an average of 97.15% of the detector points passed of VMAT plans compared to 99.36% of IMRT plans (p=0.052), the lowest pass‐rate were 91.5% for VMAT and 97.8% for IMRT. For DTA criterion, an average of 88.35% of the detector points passed of VMAT plans compared to 93.53% of IMRT plans(p=0.002). Conclusion: For the gamma criterion, VMAT and IMRT techniques can both achieve good dose verification with Delta4 detector array. However for the DTA criterion, it showed significant difference. Different criterions resulted in different pass‐rate, further studies are needed to evaluate the methods to verify the dose distribution for VMAT/IMRT plans, so appropriate method can be chosen in clinic in the future.