2981 - Evaluation of RapidArc Dynamic for Regional Nodal Breast Irradiation

Purpose/Objective(s): Radiation therapy to the whole breast or chest wall with regional nodal irradiation is standard of care for patients with node-positive breast cancer. Treatment planning is complex due to proximity of nodal target volumes to critical organs at risk (OARs), including the lungs, contralateral breast, and the heart, which can increase the risk of cardiopulmonary toxicity. RapidArc Dynamic (RAD) is a new treatment technique that integrates static IMRT beams (called Static Modulated Ports or STAMPs), a dynamic collimator, and volumetric modulated arc therapy (VMAT) into a single, hybrid delivery to leverage the strengths of both techniques. This study compares RAD with standard VMAT for regional nodal breast irradiation to evaluate dosimetric differences in target coverage and OAR sparing.

Materials/Methods: 26 treatment plans from 13 breast patients (8 left-sided, 5 right-sided) were compared. 9 patients received 4256 cGy in 16 fractions to the breast/chest wall and regional nodes; 4 patients received 4005 cGy and 3900 cGy in 15 fractions to the chest wall and nodal volumes, respectively. Deep inspiration breath hold (DIBH) was done for all left-sided patients and 3 right-sided patients. For each patient, one VMAT plan (3 partial arcs) and one RAD plan (1–2 partial arcs with 2–7 STAMPs) were generated using Eclipse v18.1 (AcurosXB dose algorithm, 0.2 cm grid). Plans were optimized to meet CCTG MA.39 constraints. Paired comparisons were performed for PTV coverage and OAR metrics per protocol requirements.

Results: RAD plans reduced mean contralateral lung and contralateral breast dose compared with VMAT. Mean heart dose was reduced by 93 cGy in left-sided and 58 cGy in right-sided cases while maintaining equivalent PTV coverage per protocol requirements, as shown in Table 1.

Conclusion: The RAD technique consistently generated dosimetrically superior plans compared to standard VMAT, reducing dose to the contralateral OARs and the heart, which reduces the risk of cardiac toxicity. This technique warrants further investigation to explore its potential for additional advancements and broader clinical applications.