2146 - Bilateral Breast Treatment in a Single Arc Using Novel Volumetric Modulated Arc Therapy with Static-Angle Modulated Ports (STAMPs)

Purpose/Objective(s): Bilateral breast cancer presents planning challenges due to complex and expansive target geometries, and proximity to critical structures (heart, lungs, LAD, esophagus). Volumetric modulated arc therapy/VMAT is a novel method that integrates dynamic arc delivery with static angle modulated ports (STAMPs) using fast, GPU-accelerated optimization. We evaluated its performance for bilateral breast treatment planning and delivery.

Materials/Methods: 10 bilateral breast cases were retrospectively planned in treatment planning system using conventional VMAT (5–6 partial arcs) and RAD (one arc with six STAMPs). Planning targets included both breasts/chest walls and comprehensive regional nodes. Paired analyses compared dosimetric endpoints for targets and organs at risk (OARs): lung V5Gy, V10Gy, V20Gy; heart Dmean and D5%; esophagus D0.03 cm³; as well as target coverage (V95%) and volume of breast getting 105% (V105%). Planning efficiency (assessed via screen recording) and delivery metrics (monitor units and total delivery time) were also compared for 3 representative cases.

Results: DVH analysis showed that 90% of RAD endpoints met or exceeded clinical goals versus 70% for VMAT. Target coverage (V95%) and breast V105% was nearly identical. RAD substantially reduced lung V5Gy by an average of 10.8% (range +0.9% to +16.3%), with modest improvements in V10Gy (2.4%) and V20Gy (0.7%), indicating robust sparing of low-dose lung regions. Mean heart dose and D5% was similar between techniques. RAD significantly improved esophagus sparing by lowering D0.03 cm³ by ~5.4 Gy (range +2.5 to +8.5 Gy). For delivery efficiency, RAD decreased total MU by ~30% and reduced total delivery time by ~62% (from 5.5-6.3 min with VMAT to 2.1-2.5 min with RAD). Planning efficiency also markedly improved, from 33–45 minutes with VMAT to 9–22 minutes with RAD.

Conclusion: RAD offers improved dosimetry and efficiency. With substantially reduced lower lung low-dose exposure, reduced esophageal high-dose regions, comparable target coverage and homogeneity, and significantly faster planning and delivery, RAD is a preferred technology to conventional VMAT for bilateral breast cancer treatment.