Performance of different Strength of Aperture Shape Controller on VMAT technique for Head and Neck, Pelvis, and Breast Cancer using Halcyon Machine

Introduction: Before starting optimization using the Volumetric Modulated Arc Therapy (VMAT) technique, the choice of the convenient aperture shape controller can be one of the most important factors that affect the plan quality.Material and Methods: Three different clinical cases were selected: head and neck cancer, pelvic cancer (prostate, cervix, and endometrium), and breast cancer treated with the VMAT technique. By keeping the same conditions, plans were reoptimized by varying aperture shape controllers (OFF, VERY LOW, LOW, MODERATE, HIGH, VERY HIGH). For plans evaluation, the homogeneity index (HI), conformity index (CI), target coverage (D98% and V98%), dose max (DMAX) and near max (D2%), treatment time delivery (MUs), and gamma index passing rate were analyzed.Results: All the studied localizations treated with the VMAT technique met clinical objectives. The VERY LOW technique achieved the best dose conformity for all localizations. A slight improvement in terms of PTV coverage and max dose is obtained in a VERY LOW technique for pelvic cancer. For breast cancer, almost the same results were obtained. However, for head and neck treatments, better results were observed with the HIGH and VERY HIGH techniques, where coverage and maximum dose improved by up to 6%.Conclusion: Changing the Strength of Aperture Shape Controller in VMAT optimization can affect dose calculation, especially in concave volumes such as Head and Neck.