ESTRO 2025 - Abstract Book

S3559

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

ESTRO 2025

Conclusion: Robust optimization may provide satisfactory CTV coverage and tissue sparing but may be overly conservative when an OAR is near the target or lack robustness if the uncertainty set is too limited. Probabilistic optimization, using user-defined probability levels to control under- and overdosage, showed more tissue sparing for the same CTV coverage, a reduction in dose variability and improved dose conformity.

Keywords: Uncertainty, Polynomial Chaos, Value-at-Risk

References: [1] Jan Unkelbach et al 2018 Phys. Med. Biol. 63 22TR02

[2] Tilly D, Holm Å, Grusell E, Ahnesjö A. Probabilistic optimization of dose coverage in radiotherapy. Phys Imaging Radiat Oncol. 2019 Apr 13;10:1-6. doi: 10.1016/j.phro.2019.03.005. PMID: 33458260; PMCID: PMC7807558. [3] Silvia Fabiano et al 2022 Phys. Med. Biol. 67 185006 [4] Perkó Z, van der Voort SR, van de Water S, Hartman CM, Hoogeman M, Lathouwers D. Fast and accurate sensitivity analysis of IMPT treatment plans using Polynomial Chaos Expansion. Phys Med Biol. 2016 Jun 21;61(12):4646-64. doi: 10.1088/0031-9155/61/12/4646. Epub 2016 May 26. PMID: 27227661.

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Digital Poster Validation of Pencil Beam Scanning Proton Therapy Beam model for the small field stereotactic treatments. Kantaram Popat Darekar 1,2 , Umesh Bharat Gayake 1,2 , Lalit Chaudhari 2 , Subhajit Panda 2 , Siddhartha Laskar 2,3 , Sanjay D Dhole 4 , Bhushankumar J Patil 1 1 Department of Physics, Abasaheb Garware College, Pune, India. 2 Department of Radiation Oncology, Advanced Centre for Treatment, Research, and Education in Cancer, Tata Memorial Centre, Homi Bhabha National Institute, Navi Mumbai, India. 3 Department of Radiation Oncology, Tata Memorial Hospital, Tata Memorial Centre, Homi Bhabha National Institute, Mumbai, India. 4 Department of Physics, Savitribai Phule Pune University, Pune, India Purpose/Objective: Validating the beam data model is an essential step in commissioning radiation therapy delivery systems. The growing use of stereotactic techniques drives the increasing adoption of small fields in clinical practice. Clinical commissioning guidelines, such as AAPM TG 185, recommend beam data validation for rectilinear fields as small as 2 cm. In pencil beam scanning (PBS) proton therapy, dose delivery to small stereotactic targets is associated with significant uncertainties due to the inherent characteristics of the pencil beam. Therefore, validating the beam data model for small target delivery in homogeneous and inhomogeneous media is critical. This study aims to validate the clinical beam data model for PBS proton therapy in small target treatments within a homogeneous medium. Material/Methods: A beam data model was created in the Raystation Treatment Planning System (TPS) (v12A, RaySearch Laboratories, Stockholm, Sweden) for the IBA Proteus Plus PBS Proton Therapy delivery system. Beam data, including spot size, output, and range, were measured, and the beam model was generated as per TPS recommendations. Beam model validation plans were generated using the Monte Carlo algorithm. A total of 19 plans, with target sizes ranging from 0.5 to 2.5 cm (in 0.5 cm increments), modulation up to 5 cm, and depths up to 14 cm, were created, including scenarios with and without a range shifter. Measurements were performed in a water medium for longitudinal SOBP, inline and crossline lateral profiles, and output at the cube center using an IBA CC01 chamber and RAZOR diode. TPS-calculated and RFA-measured results were compared for modulation (M95), range accuracy (R90, R80), distal dose falloff (DDF), field size, and penumbra later for longitudinal and lateral profiles.