SU‐E‐T‐886: Exploration of SBRT Lung Treatment Using the First Non‐Commercial VMAT

Abstract

Purpose: The beamlet‐based IMRT‐SBRT has two widely‐recognized deficiencies: an elevated MU and a reduced MU‐to‐cGy coefficient. To address these issues, we developed our own version of VMAT. A thorough literature search indicates that this is the first non‐commercial VMAT in the United States. Our objectives are 1) to minimize MU; 2) to maximize delivery efficiency and 3) to provide IMRT‐SBRT‐comparable plans. Methods: All VMAT‐SBRT plans consisted of a single arc of 180 equally spaced beams. Our VMAT was designed to simultaneously optimize both MLC apertures and aperture MU weights. A novel feature of our VMAT planning system was the inclusion of a normal tissue objective (NTO) function into the total dose‐volume based quadratic objective function. Five VMAT‐SBRT plans were computed and compared with corresponding IMRT‐SBRT plans. Our VMAT‐SBRT plans were delivered in RapidArc mode on a RapidArc‐enabled Varian Trilogy machine. Results: We found that the mean MU for the VMAT‐SBRT plans was 2052±108, while that for the IMRT‐SBRT plans was 3790±63. The MU‐to‐cGy ratio was 1.15±0.06 for the VMAT‐SBRT plans, while the MU‐to‐cGy ratio was 2.11±0.04 for the IMRT‐SBRT plans. The mean delivery time for the IMRT‐SBRT plans was 6.32±1.06 min (600 MU/min), while that for the VMAT‐SBRT plans was only 1.25 min. The mean target dose homogeneity index HI for the IMRT‐SBRT plans was 0.0535±0.0001, while that for the VMAT‐SBRT plans was 0.0366±0.0028. The mean PTV dose conformity PIPTV for the VMAT‐SBRT plans was 1.421±0.0311, while that for the IMRT‐SBRT plans was 1.466 ±0.0028. Conclusions: Based on our preliminary results, we conclude that our own version of VMAT‐SBRT can significantly increase plan delivery efficiency, enhance energy use efficiency, and improve target dose homogeneity and conformity. It is a viable and safe substitute for IMRT‐SBRT.