SU-E-J-140: Dual-Gated Radiotherapy with PTV Partition Technique: A Feasibility Study

Abstract

Purpose: Dual-gated radiotherapy is a promising method to reduce overall treatment time in which a dose is delivered at inhale and exhale phases. However, problems still remain associated with the phase shift and the target motion artifact. Dual-gated method deals with both phases — inhale and exhale, hence the delivered dose uncertainties due to the residual motion may be doubled. In order to account for these uncertainties, we applied PTV partition technique to dual-gated radiotherapy method. Methods: An IMRT plan for a lung cancer patient was optimized in Eclipse TPS at exhale phase. The PTV on the exhale CT was partitioned into three regions along the superior-inferior axis; head, mid, and tail region. The dose distribution on PTV was reformed as follows: a) no dose is given to the head region, b) a gradient dose (zero to the prescription dose) is given to the mid region, and c) a hundred percent of prescription dose is given to the tail region. The reformed exhale phase dose distribution and structures were deformed to the inhale phase CT using MIM software. Thereafter the dose distribution on PTV at inhale phase was reformed in order that complement of the prescription dose is given to each region. Results: The dose-volume histogram for PTV in the dual-gated plan with partitioned PTV was comparable to that in the conventional gating plan while the presented technique gives robustness to the residual motion. Conclusion: The proposed method using the PTV partition technique is promising to assess dose uncertainties due to the phase shift and the target motion artifact. Further assessment of the robustness to the residual motion by experiments using thorax phantom is warranted in this regard.