DynamicARC Proton Therapy in Conjunction With LETd Optimization For Bilateral Breast Cancer: Assessing RBE-Weighted Doses To Targets and Critical Structures

Document Type

Conference Proceeding

Publication Date

12-2025

Publication Title

International Journal of Particle Therapy

Abstract

Background and Aims: Enhanced dose-averaged linear energy transfer (LETd) at the end of the proton beam range may increase toxicity risks. DynamicARC proton therapy has the potential to offer more conformal treatment plans with efficient delivery. This study evaluates DynamicARC’s feasibility for synchronous bilateral breast cancer (SBBC) planning and quantifies RBE-weighted doses for target volumes and OARs. Methods: An anonymized CT dataset of a bilateral breast cancer patient was utilized. The total clinical target volume included bilateral breasts, axillary nodes (AXN), internal mammary nodes (IMN), and supraclavicular nodes (SCVN). DynamicARC plans were generated with two partial arcs with a single isocenter delivering 50 Gy(RBE) in 25 fractions. The first optimization (non-LETOpt plan) used a constant RBE (cRBE) of 1.1 without LETd objectives, while the second (LETOpt plan) added LETd constraints. Robust optimization accounted for setup (±5 mm) and range (±3%) uncertainties. RBE-weighted dose distributions [D + (D × kLETd), where k=0.055 µm/keV](1) were calculated and compared to nominal doses of the corresponding plans (non-LETOpt and LETOpt). Results: Compared to nominal doses, RBE-weighted target coverage was comparable for breasts (D95 and D98: ±0.8%) but higher for AXN+SCVN (D95: up to 3.6% and 3.5%) and IMN (D90: 7.9% and 13.2%) in non-LETOpt and LETOpt plans, respectively. RBEweighted OAR doses were higher than corresponding nominal doses, except skin D1cc, reduced by 1% in LETOpt plan. Lung doses remained within acceptable limits (V20< 14%, V5< 42%, Dmean< 9 Gy(RBE)), as did esophagus Dmean (< 9Gy(RBE)) and heart metrics (Dmean< 1 Gy(RBE)). The skin RBE-weighted D0.03cc increased to 51.8 Gy(RBE) in the non-LETOpt plan but remained below the prescription dose in the LETOpt plan when compared to nominal doses. The ribs RBE-weighted D0.5cc increased by up to 8% in the non-LETOpt plan and 2% in the LETOpt plan, relative to their respective nominal doses. Conclusions: This study is the first to evaluate RBE-weighted dose distributions in DynamicARC proton therapy with LETd optimization for SBBC. LETd objectives improved the target coverage (AXN +SCVN and IMN) while maintaining acceptable OAR doses and reducing RBE-weighted doses to skin and ribs, potentially mitigating skin toxicities and rib fracture risks. Further research is needed to confirm these findings and their clinical relevance.

Volume

17

Issue

Suppl

First Page

100768

Last Page

100768

Comments

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

DOI

10.1016/j.ijpt.2025.100768

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