A Retrospective Review on Stereotactic Radiosurgery Cases Planned with Dynamic Conformal Arcs Versus Volumetric Modulated Arc Therapy

Abstract

This study aimed to acquire an average value of plan quality metrics by retrospectively analyzing past stereotactic radiosurgery (SRS) treatment plans. The study was also designed to compare the plan quality metrics between single-target Dynamic Conformal Arc (DCA) and multi-target Volumetric Modulated Arc Therapy (VMAT) plans. A total of 253 LINAC-based SRS plans treated in 2017 at our institution were reviewed. A total of 605 lesions were included in these plans as treatment targets. 156 plans were generated with a DCA technique treating single target in each plan, and 97 plans used a VMAT technique to treat multiple targets simultaneously in a single plan. The prescription dose was normalized to 20Gy for all plans for this analysis. Two plan quality metrics, tumor Conformity Index (CI) and normal tissue volume receiving more than 12Gy (V12Gy), were calculated for each target. The results were stratified based on target size and compared between different techniques. For multi-targets VMAT plans, the distance of a target to the nearest other target and the number of targets being treated in the same plan were calculated for each target to evaluate their impact on V12Gy. For the subgroups of target volume < 0.2cc, 0.2-0.5cc, 0.5-1.0cc, 1.0-2.0cc, and 2.0-4.0cc, the mean (±SD) CI were 2.1 (±0.3), 1.9 (±0.2), 1.8 (±0.3), 1.6 (±0.2), and 1.6 (±0.1), respectively, in DCA plans and 1.8 (±0.4), 1.5 (±0.2), 1.4 (±0.2), 1.3 (±0.2), and 1.3 (±0.1), respectively, in VMAT plans. The mean V12Gy were 1.2cc, 1.9cc, 3.5cc, 5.2cc, and 7.4cc, respectively, in DCA plans and 1.3cc, 2.2cc, 3.2cc, 4.7cc, and 7.8cc, respectively, in VMAT plans. The V12Gy for a target in VMAT plan did not show apparent dependence on the distance between targets or the total number of targets in single VMAT plan. The average performance level of CI and V12Gy were established based on previous cases and can be used as benchmark for future SRS planning. The multi-target VMAT plans produced consistently lower CI and kept the normal tissue 12Gy per target comparable to DCA plans.