SU‐E‐T‐630: Feasibility Study of Volumetric Modulated Arc Therapy with Constant Dose Rate for Endometrial Cancer

Abstract

Purpose: To investigate the feasibility, efficiency, and delivery accuracy of volumetric modulated arc therapy with constant dose rate (VMAT‐CDR) for whole pelvic radiotherapy of endometrial cancer. Methods: The nine‐field intensity‐modulated radiotherapy (IMRT), volumetric modulated arc therapy with variable dose rate (VMAT‐VDR), and VMAT‐CDR plans were created for 9 patients with endometrial cancer undergoing whole pelvic radiotherapy. The dose distribution of planning target volume (PTV), organs at risk (OARs) and normal tissue (NT) were compared. The monitor units (MUs) and treatment delivery time were also evaluated. For each VMAT‐CDR plan, a dry run was performed to assess the dosimetric accuracy with MatriXX from IBA. Results: Compared with IMRT, the VMAT‐CDR plans delivered a slightly greater V20 of bowel, bladder, pelvis bone and normal tissue, but significantly decreased the dose to the high dose region of rectum and pelvis bone. The monitor units decreased from 1105 with IMRT to 628 with VMAT‐CDR. The delivery time also decreased from 9.5 min to 3.2 min. Very similar dose distribution was found in the VMAT‐VDR and VMAT‐CDR plans. The average gamma pass rate was 95.6% at the 3%/3 mm criteria with MatriXX pre‐treatment verification for nine patients. Conclusion: Volumetric modulated arc therapy with constant dose rate can achieve comparable plan quality with significant shorter delivery time and smaller number of MUs compared with IMRT for endometrial cancer patients undergoing whole pelvic radiotherapy. It can be accurately delivered and be an alternative to IMRT on the linear accelerator without variable dose rate capability. This work is supported by the grant project: National Natural Science Foundation of China (No. 81071237).