ESTRO 2024 - Abstract Book

S4620

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

ESTR0 2024

[2] Zimmermann L, Knäusl B, Stock M, Lütgendorf-Caucig C, Georg D, Kuess P. An MRI sequence independent convolutional neural network for synthetic head CT generation in proton therapy. Z Med Phys. 2022 May;32(2):218 227. doi: 10.1016/j.zemedi.2021.10.003. Epub 2021 Dec 15. PMID: 34920940; PMCID: PMC9948837. [3] Maspero M, van den Berg CAT, Landry G, Belka C, Parodi K, Seevinck PR, Raaymakers BW, Kurz C. Feasibility of MR only proton dose calculations for prostate cancer radiotherapy using a commercial pseudo-CT generation method. Phys Med Biol. 2017 Nov 21;62(24):9159-9176. doi: 10.1088/1361-6560/aa9677. PMID: 29076458.

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Digital Poster

LETd vs dose-based proton plan: outcomes for brainstem and optical structures in craniopharyngioma

Alfredo Mirandola 1 , Giuseppe Magro 1 , Luca Trombetta 1 , Eleonora Rossi 1 , Francesca Colombo 2 , Jessica Franzetti 2 , Alberto Iannalfi 2 , Marco Rotondi 2 , Sabina Vennarini 3 , Ester Orlandi 4 , Mario Ciocca 5 1 CNAO Foundation, Medical Physics, Pavia, Italy. 2 CNAO Foundation, Radiotherapy Department, Pavia, Italy. 3 Fondazione IRCCS Istituto Nazionale dei Tumori, Paediatric Radiotherapy Unit, Milan, Italy. 4 CNAO Foundation, Head of Radiotherapy Department, Pavia, Italy. 5 CNAO Foundation, Head of Medical Physics, Pavia, Italy

Purpose/Objective:

To compare the dose-averaged linear energy transfer (LETd)-based proton plans to conventional dose-based proton plans in order to assess the brainstem and optical structures sparing while preserving the recommended clinical objectives for paediatric patients affected by craniopharyngioma.

Material/Methods:

Within a homogeneous cohort of paediatric patients with craniopharyngioma, we selected 15 cases with the target partially comprising both optical nerves and the optic chiasm, and/or near to the brainstem and optical nerves. Prescription dose (DRBE) was 54 Gy(RBE, relative biological effectiveness) delivered in 30 fractions. The following robustness parameters were adopted for plans optimisation: 2 mm setup errors, 3% range uncertainty (1). A dose constraint of D1% ≤ 54 Gy(RBE) was set for both the brainstem and the optic pathways. Due to the lesions' central symmetry and the above mentioned organs at risk (OARs) location, the typical beam arrangement used for these treatments included three orthogonal beam entrances—one from the left, one from the right, and one from the vertex. To minimize high LET deposition to the OARs, the clinically approved dose-based plans were optimised by using mitigation strategies, such as beam-related dose penalty weights and/or Bragg peaks dose deposition minimization at the edge of the critical structures. The same beam arrangement was used to optimize the LETd-based plans, but additional LETd-based objectives, recently integrated in the plan optimization module of RayStation (v2023B), were added to the cost function. Specifically, for each beam, the maximum LETd of particles depositing a DRBE greater than 15-20 Gy was reduced to the value of 4 KeV/µm for the brainstem and optical structures. The D1% ≤ 54 Gy(RBE) dose constraint for the optic structures and brainstem was examined in this investigation. D0.01cc was additionally evaluated for the latter OAR. Two variable RBE model models were then used (2, 3) to compute both the dose-based and LETd-based dose distributions.