ESTRO 2025 - Abstract Book

S3527

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

ESTRO 2025

Conclusion: PAT combined with LET optimization has great potential for improving plan quality by reducing dose (D RBE=1.1 ) to visual OARs and cerebrum. Moreover, LET optimization as currently available can be an effective surrogate for directly optimizing variable RBE-weighted dose (D McN ).

Keywords: LET optimization, Proton Arc Therapy, Neuro

References: [1] McNamara AL, Schuemann J, Paganetti H. A phenomenological relative biological effectiveness (RBE) model for proton therapy based on all published in vitro cell survival data. Phys Med Biol. 2015 Nov 7;60(21):8399-416. doi: 10.1088/0031-9155/60/21/8399. [2] de Jong BA, Battinelli C, Free J, Wagenaar D, Engwall E, Janssens G, Langendijk JA, Korevaar EW, Both S. Spot scanning proton arc therapy reduces toxicity in oropharyngeal cancer patients. Med Phys. 2023 Mar;50(3):1305 1317. doi: 10.1002/mp.16098.

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Mini-Oral Towards a novel treatment platform for proton therapy of ocular tumors on a non-dedicated beam line Patrick Roisl 1 , Andreas Resch 1,2 , Alexander Ableitinger 1 , Antonio Carlino 1 , Andreia Maia Oliveira 1 , Dietmar Georg 2 , Roman Dunavölgyi 3 , Matthias Moll 4 , Carola Lütgendorf-Caucig 4 , Wolfgang Sauerwein 4 , Eugen Boris Hug 4 , Markus Stock 1,5 1 Medical Physics, MedAustron Ion Therapy Center, Wiener Neustadt, Austria. 2 Radiation Oncology, Medical University Vienna, Vienna, Austria. 3 Ophtalmology, Medical University Vienna, Vienna, Austria. 4 Radiation Oncology, MedAustron Ion Therapy Center, Wiener Neustadt, Austria. 5 General and Translational Oncology and Hematology, Karl Landsteiner University of Health Sciences, Krems, Austria Purpose/Objective: Proton therapy for ocular tumors is established for several decades. Its historic technological implementation with patients in seated position in dedicated, specific treatment rooms allows for high accuracy. Our novel image-based approach aims to achieve similar accuracy by utilizing a general-purpose proton treatment room, a vertical beam line, with the patient in supine position. Material/Methods: Several development initiatives were performed in parallel and can be categorized accordingly: Accelerator development including beamline design, eye tracking hard- and software, in-room clip-based image guidance and treatment planning. More specifically, a patient specific brass collimator holder was developed as accessory to the fixed vertical beam line nozzle to allow treatment in supine position. As the ideal target position requires patient specific gaze angles, CT-and MRI compatible gaze and tracking device was attached to the treatment couch and mask system. Finally, workflows for treatment preparation and treatment planning were developed to facilitate integration of high-resolution CT and MR imaging combined with further information by the ophthalmologist (e.g. fundoscopy and clip placement). Results: The synchrotron was dosimetrically commissioned reducing the nominal spill length of ten seconds to two seconds including existing range-shifter as scattering element and patient-specific collimator. Beam-on times for several tumor sizes reduced to 1-3 minutes for a fractional dose of 15 Gy RBE. Film measurements revealed excellent quality of the lateral penumbra (LP 80-20) of 0.7-2.0 mm at depths of 2.5-35 mm in water, underlining the stereotactic characteristics of dose delivery. The distal penumbra (DP 90-10) was 1.5 mm at depths of 25 mm. The existing MC dose algorithm and pencil beam scanning model are used showing excellent agreement of predicted vs