Synchronous Bilateral Chest Wall and Regional Nodal Irradiation: Dosimetric Comparison of Spot-Scanning Proton Arc Therapy Versus Intensity Modulated Proton Therapy

Document Type

Conference Proceeding

Publication Date

12-2025

Publication Title

International Journal of Particle Therapy

Abstract

Background and Aims: To investigate the feasibility and normal tissue sparing of Spot-scanning Proton Arc (SPArc) therapy for patients receiving synchronous bilateral chest wall and regional nodal treatment. Methods: Fifteen patients with loco-regionally advanced breast cancer who underwent a CT-based simulation for radiation planning were selected. Seven patients had bilateral intact breasts, and eight patients had undergone bilateral total mastectomies (five of whom had reconstruction with either permanent implants or tissue expanders, and three had no reconstruction). Clinical target volumes for the breast or chest wall and the axillary levels I-III, supraclavicular, posterior cervical, and internal mammary nodal regions were contoured per the RADCOMP Breast Cancer Atlas. Near-surface skin rind volumes were defined as the volume bound by the breast/chest wall from the skin surface to 3 mm depth. For each patient, the SPArc and IMPT plans were generated with a prescription dose of 50 Gy in 25 fractions, with the goal of 95% prescription dose coverage of 95% of target volumes. Near-surface dose optimization was applied for both plans. Dosimetric parameters of target volume and organ-at risks, including the skin rind, were evaluated. Paired t-tests were used for the statistical analysis of normally distributed parameters; otherwise, the Wilcoxon rank-sum tests were employed. Results: With comparable target coverage, SPArc significantly reduced the dose to the lungs, the heart and the left anterior descending artery, compared to IMPT. Notably, SPArc reduced the mean left lung dose by 50.6% (452.93 cGy ± 94.78 cGy vs. 918.20 cGy ± 192.53 cGy, p < 0.001) and the mean right lung dose by 40% (492.13 cGy ± 91.47 cGy vs. 816.68 cGy ± 296.12 cGy, p < 0.001). SPArc significantly decreased the average skin rind dose by an average of 4.16 Gy (40.8 cGy ± 2.6 Gy vs. 44.9 cGy ± 2.1 Gy, p < 0.001). Conclusions: SPArc demonstrates dosimetric superiority over IMPT in synchronous bilateral chest wall and regional nodal irradiation, achieving significant sparing of organs at risk, notably the lung and near-surface region

Volume

17

Issue

Suppl

First Page

101128

Last Page

101128

Comments

63rd Annual PTCOG (Particle Therapy Cooperative Group) Conference, June 2-7, 2025, Buenos Aires, Argentina

DOI

10.1016/j.ijpt.2025.101128

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