ESTRO 2025 - Abstract Book

S3561

Physics - Optimisation, algorithms and applications for ion beam treatment planning

ESTRO 2025

1.5%), focusing on minimum tumor coverage and maximum dose to gastrointestinal (GI) structures. Inter-fraction robustness was analyzed by recalculating dose distributions on control CTs acquired during the treatment course.

Results: SHArc plans can achieve comparable or improved dose conformity and enhanced LETd distribution compared to the clinical standard at HIT, 3 while preserving maximum dose in the organs at risk. The maximal LETd boost was limited by the GTV size, with a range from about 50 to 90 keV/μm for the largest and smallest tumor. The MU-Based EL method provided more robust target coverage, while the Central EL method allowed greater LETd escalation, with the highest LETd in the tumor center. As shown in Figure 1, inter-fraction robustness challenges were observed due to anatomical variations, particularly air filling in the GI tract, resulting in high-dose regions and reduced tumor coverage. Nevertheless, the MU-Based EL method exhibited smaller fluctuations in dose distribution compared to the Central EL.

Conclusion: Achieving an optimal balance between dose conformity, LETd modulation, and plan robustness remains challenging. Future research will focus on improving robustness to inter-fraction anatomical variations through advanced planning strategies, thereby enhancing the clinical applicability of SHArc in carbon ion therapy.

Keywords: Pancreatic cancer, LETd-boosting, Arc therapy

References: 1 Mein S, Tessonnier T, Kopp B, Harrabi S, Abdollahi A, Debus J, et al. Spot-Scanning Hadron Arc (SHArc) Therapy: A Study With Light and Heavy Ions. Adv Radiat Oncol 2021;6. 2 Mein S, Tessonnier T, Kopp B, Schemers C, Debus J, Abdollahi A, et al. Biological Dose Optimization for Particle Arc Therapy Using Helium and Carbon Ions. Int J Radiat Oncol Biol Phys 2021. 3 Liermann J, Naumann P, Hommertgen A, et al. Carbon ion radiotherapy as definitive treatment in non-metastasized pancreatic cancer: Study protocol of the prospective phase II PACK-study. BMC Cancer. 2020;20(1):1-7. doi:10.1186/s12885-020-07434-8