ESTRO 2025 - Abstract Book

S3473

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

ESTRO 2025

Material/Methods: For each patient, the proposed novel pBAO solves a total-beam-space BAO problem[1], in which a candidate set of 72 equiangular beams is optimised using a cost-function that includes penalties for the targets and most important OARs, and a term to sparsify the beam space. For generation of the optimal N-beam plan, the N highest weighted beams with at least 180/N degree spacing are selected. The optimal robust N-beam plan is then generated using fully-automated wish-list driven multi-criteria plan generation[2] as implemented in SISS-MCO[3]. For validation in 10 oropharynx patients, the OARs considered in the total-beam-space BAO problem were related to NTCPs for xerostomia and dysphagia in accordance with the Dutch National Protocol for Model-Based Selection[4]. Previously, superiority of SISS-MCO over manual planning was demonstrated[5]. SISS-MCO plans are by design Pareto-optimal for spot intensities. For validation of pBAO , 4- and 6-beam pBAO plans were compared to plans generated for our clinically applied 4- and 6-field beam-angle templates. Similar to generation of pBAO plans (above), SISS-MCO was also used for automated generation of the template plans, avoiding planning bias. To ease analyses, all generated plans were normalised to the clinically requested target coverage. Results: Solving the total-beam-space problem took on average 52 min. pBAO plans were dosimetrically superior to 4-field and 6-field clinical template plans. Figure 1 shows lower doses in NTCP-related OARs with comparable target coverage as in corresponding clinical template plans. For 4- and 6-field plans, improvements in NTCPG2_xerotomia + NTCPG2_dysphygia were 3.0 (range: 1.1-5.8, p=0.002) and 2.4 (range: 0.0-5.0, p=0.004) %-point compared to corresponding clinical templates. For G3, these improvements were 1.2 (range: 0.3-2.8, p=0.01) and 0.8 (range: -0.1 2.1, p=0.004) %-point. Figure 2 shows for an example patient the 4-field and 6-field pBAO angles, the clinical templates, and the corresponding dose distributions.