ESTRO 2025 - Abstract Book

S2748

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2025

1028

Digital Poster The GammaPod reduces organ-at-risk dose and creates more conformal plans compared to VMAT when delivering accelerated partial breast irradiation Elizabeth M Nichols, Naru Lamichhane, Mariana Guerrero, Sarah McAvoy, Baoshe Zhang, Jessica Richardson, Stewart J Becker Radiation Oncology, University of Maryland School of Medicine, Baltimore, USA Purpose/Objective: The GammaPod (Xcision Medical Systems, Columbia MD)(1-3) is a novel breast only radiosurgery device that delivers radiation in the prone position with 25 Co-60 sources that rotate around the breast compared to the body. The breast is immobilized with a system of cups that utilizes a vacuum to pull the breast away from the chest wall and to hold the breast rigid to minimize motion during treatment and between imaging and treatment. As with any new modality there are questions on how it compares to current methods. In the is study we present a 5 fraction APBI dosimetric comparison between the GammaPod and the most common method of partial breast irradiation, VMAT Material/Methods: Patients who had undergone GammaPod as a single fraction boost (on protocol) to their adjuvant whole breast were selected for this study. These patients had both a CT with the GammaPod cup and a standard prone CT scan without the cup. The use of both CT allows for the plans to be created exactly how they would be treated in the clinic. Both CTs were contoured and planned using with the standard APBI margins for each technique, 10mm GTV to CTV margin for both and 3mm and 5mm CTV to PTV margins for the GammaPod and VMAT cases, respectively. The plans were normalized to cover 95% of the PTV with 30 Gy in 5 fractions. OAR doses for the whole breast and heart were analyzed as well as the conformality (CI) and homogeneity indices (HI). Both the GammaPod and VMAT plans were performed by an expert planner in each technique.

Results:

Compared to the VMAT plans, GammaPod led to reduced OAR doses for max heart dose (5.3 ± 2.7 vs 9.1 ± 3.7 Gy), whole breast V15Gy (26.6 ± 7.2 vs 40.3 ± 11.9 %), whole breast V30Gy (8.6 ± 3.1 vs 18.7 ± 6.9 %), and CI (1.11 ± 0.11 vs 2.17 ± 0.42). GammaPod and VMAT achieved the same hotspots (118% ± 5% vs 119.7% ± 2%) and HI (1.12 ± 0.05 vs 1.15 ± 0.02). Conclusion: The use of the GammaPod was associated with a more conformal dose distribution and lower OAR doses to the heart. It was also associated with less dose spillage to the normal whole breast which can lead to less fibrosis and improved cosmetic outcomes for patients.