Document Type : Original Paper
Faculty of Sciences, LPHE-M&S, Mohammed V University, Rabat
Hassan First University of Settat, High Institute of Health Sciences, Laboratory of Sciences and Health Technologies, Settat, Morocco
Private Hospital Casablanca-AKDITAL
Department of physics, University of Mohammed 1st, Oujda, Morocco
Departement of Physics, Laboratory of High Energy Physics, Modelling and Simulation, Faculty of Science, Mohammed V Agdal University, Rabat, Kingdom of Morocco
Background Before starting optimization for VMAT technique, the choice of the convenient strength aperture shape controller can be one of the most important factor that affect the plan quality. It is necessary to evaluate different optimization options for different localizations.
Materials and methods Three different clinical cases including Head and Neck, Pelvic (Prostate, Cervix and Endometrium) and Breast Cancer treated using VMAT technique were chosen. Treatment plans were generated with Eclipse TM treatment planning software (v16.1.0) using a 6X flattening filter free energy and 600 MU/min dose rate. By keeping the same conditions, plans were reoptimized by varying aperture shape controller (OFF, VERY LOW, LOW, MODERATE, HIGH, VERY HIGH). For plan evaluation, homogeneity index, conformity index, target coverage, dose max and near max and the treatment time delivery (HI, CI, D98%, DMAX, D2%, MUs and gamma index passing rate) were analyzed.
Results: All studied localizations treated by VMAT technique satisfied the clinical objectives. VERY LOW technique achieved the best dose conformity for all studied localizations. D98% for treating Pelvic was very closed for all optimization techniques, between 96,5% and 97% that was obtained for VERY LOW. This variations was similar for V98% that was between 95% and 96% for all optimization technique except in VERY HIGH that was under 95%. The lower maximum and near maximum dose also obtained in VERY LOW with 106,5% and 103,75% respectively. DMAX was between 110% and 110.5% for all techniques, and between 106% and 106.5% for D2% always with 0.5% lower in VERY LOW technique.
Conclusion The effect on changing strength aperture shape controller for optimization on VMAT dose calculation can be significant. The results disclosed that using HIGH and VERY HIGH technique for Head and Neck can improve the dose coverage, dose max and significantly reduced the treatment time compared to LOW technique.