Impact of Combining Advanced Dynamic Collimator Arc Therapy with Flattening Filter-Free Beams on Plan Quality and Delivery Efficiency In Postmastectomy Radiotherapy
Abstract
Purpose
RapidArc Dynamic (RAD) in Eclipse, version 18.1 integrates dynamic collimator rotation with static angle modulated ports (STAMPs) into arc to improve plan quality and treatment time. Flattening filter–free (FFF) beams further reduce beam-on time through higher dose rates. This study evaluated the dosimetric impact and delivery efficiency of combining RAD with FFF beams in postmastectomy radiotherapy (PMRT).
Methods
Twenty-four PMRT patients (12 left- and 12 right-sided) were retrospectively analyzed. Two RAD plans were generated with Eclipse, version 18.1 for TrueBeam using 6 MV (RAD_6X) and 6 MV FFF beams (RAD_6F). RAD plans used a single half arc starting at 60° contralaterally to the midline, with dynamic collimator rotation optimized between three STAMPs. STAMP angles were fixed at 300°, 350°, and 120° for left-sided cases, and symmetrically mirrored for right-sided cases. These were compared against a conventional 4-split arcs VMAT plan using a 6 MV beam (VMAT_6X). All plans prescribed 50 Gy in 25 fractions using virtual bolus technique and were normalized to PTV D50%. PTV D2%/D95%, mean dose to heart, contralateral breast, and lungs, and beam-on time were analyzed using Bonferroni corrected paired t-tests.
Results
While PTV D2% showed no significant differences, RAD plans showed significantly relative increases in PTV D95% over VMAT_6X (1.0%/1.3% for RAD_6X/RAD_6F, p<0.001). Mean dose reductions (RAD_6X/RAD_6F) relative to VMAT_6X were 11.0%/12.4% for heart, 17.3%/19.8% for contralateral breast, and 10.4%/11.6% for lungs (all p<0.001). RAD_6F improved target coverage and OAR-sparing significantly more than RAD_6X. RAD_6F reduced beam-on time by 41.7% relative to VMAT_6X, significantly outperforming the 13.7% reduction observed with RAD_6X (both p<0.001).
Conclusion
Combining RAD with FFF beams improved target coverage and OAR-sparing while reducing beam-on time significantly more than conventional multi-arc VMAT, making RAD a highly efficient and effective solution for PMRT with the potential to enhance clinical throughput and reduce toxicities.