ESTRO 2024 - Abstract Book

S4709

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

ESTR0 2024

References:

Bolsa ‐ Ferruz, Marta; Palmans, Hugo; Boersma, David; Stock, Markus; Grevillot, Loïc (2021): Monte Carlo computation of 3D distributions of stopping power ratios in light ion beam therapy using GATE ‐ RTion. In: Med. Phys. 48 (5), S. 2580– 2591. DOI: 10.1002/mp.14726.

Burigo, Lucas; Greilich, Steffen (2019): Impact of new ICRU90 key data on stopping-power ratios and beam quality correction factors for carbon ion beams. In: Phys. Med. Biol. 64 (19), S. 195005. DOI: 10.1088/1361-6560/ab376e.

2809

Digital Poster

Robust margin evaluation by probabilistic dose accumulation for IMPT thoracic wall patients

Tim C Franssen, Bojan Štrbac, Pieter R.A.J. Deseyne, Hans A Langendijk, Stefan Both, Dirk Wagenaar

UMCG, Radiotherapy, Groningen, Netherlands

Purpose/Objective:

In the Netherlands, a subset of breast cancer patients is eligible for proton irradiation through the model-based approach. Breast patients can qualify based on a reduction in either excess risk on an acute coronary event (ACE) or the occurrence of secondary tumours in the lungs or contralateral breast. This study will investigate if the current setup uncertainty can be reduced while maintaining adequate CTV coverage to further reduce dose to organs-at-risk (OAR).

Material/Methods:

A retrospective study was performed on 13 post-total mastectomy breast cancer patients who underwent Intensity Modulated Proton Therapy (IMPT) for 15 fractions x 2.67Gy (RBE) at our institute. A constant RBE of 1.1 was considered. Patients were selected for proton treatment according to the Dutch National breast cancer patients selection protocol [5]. The CTV consisted of thoracic wall and regional lymph nodes (axillary levels I through IV, the interpectoral and internal mammary nodes). The treatment plan consisted of 2 to 3 anterior fields robustly optimized for 5mm setup uncertainty and 3% range uncertainty. Each field was planned with 3 times layer repainting to mitigate the interplay effect. In addition to the initial treatment planning CT, each patient underwent a weekly verification CT to monitor potential changes in anatomy over the course of treatment. For the purpose of this study, robustly optimized plans for a setup uncertainty of 4mm, 3mm, 2mm and 1mm with 3% range uncertainty were generated using an in-house developed script, as described by Wagenaar et al. which uses dose-mimicking to ensure consistent treatment plan quality [6].

The robustness setup uncertainty was determined based on systematic and random errors. The systematic error consists of machine position error determined based on weekly machine QA (6D robotic table, mechanical