ESTRO 2024 - Abstract Book

S4701

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

ESTR0 2024

3) Takakusagi Y, Katoh H, Kano K, Anno W, Tsuchida K, Mizoguchi N, Serizawa I, Yoshida D, Kamada T. Preliminary result of carbon-ion radiotherapy using the spot scanning method for prostate cancer. Radiat Oncol. 2020 May 27;15(1):127.

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Multiple anatomical scenarios in plan optimization for particle therapy of gynaecological tumors.

Alessandro Vai 1 , Silvia Molinelli 1 , Amelia Barcellini 1,2 , Giuseppe Magro 1 , Alfredo Mirandola 1 , Stefania Russo 1 , Viviana Vitolo 1 , Jessica Franzetti 1 , Ester Orlandi 1 , Mario Ciocca 1 1 National Center for Oncological Hadrontherapy (CNAO), Radiotherapy Department, Pavia, Italy. 2 University of Pavia, Internal Medicine and Medical Therapy, Pavia, Italy

Purpose/Objective:

Improved dose conformity provided by particle therapy with respect to photons is more vulnerable to range and anatomical variations. Clinical treatment planning systems permit therefore the inclusion of possible scenarios of uncertainties into a robust optimization algorithm [1]. Nevertheless, including additional CTs [2] or virtual imaging [3] could not be taken as a rule to mitigate the impact of unpredicted anatomical variations for all tumours and anatomical districts. In this work, we investigated whether multiple-CT optimization for gynaecological particle therapy planning might improve plan robustness to anatomical changes during the treatment course thus reducing the need for plan adaptation.

Material/Methods:

Five consecutive gynaecological patients with vulvar adenoid cystic carcinoma (ACC) who received mixed pencil-beam scanning (PBS) carbon-ion (C-ion) and protons beams were included in this study. We administered radiotherapy within a bimodal approach, consisting of i) a first phase of C-ion irradiation (CIRT) as an early boost to areas of macroscopic tumour and a second phase of proton beam radiotherapy (PBT) on areas with an increased risk of recurrence in case of unresectable disease; ii) PBT followed by CIRT on the surgical bed in case of adjuvant treatment on positive margins. The prescription dose was 54 Gy(RBE) with PBT and 24 Gy(RBE) with CIRT. Each patient had a planning CT (p-CT) and at least two re-evaluative CTs (rv-CT1, rv-CT2) acquired during the treatment course. In parallel with clinical plans prepared on p-CT with standard uncertainties parameters (5mm + 3.5%), we optimized robust PBT and CIRT plans (rob_plan) including rv-CT1 in the optimization for a total of ten plans (5 CIRT and 5 protons). Plans were optimized with 3 to 5 horizontal and vertical beam ports (depending on target dimensions) with Raystation TPS (v.11b). For gynaecological patients target coverage and anorectal dose max constraint (D1<43 Gy(RBE) and 20 Gy(RBE) for protons and CIRT plans respectively) were defined as robust in the optimization algorithm. Differences between plan recalculation on re-CT2 and nominal plan dose values were estimated for the target (D99, D95 and D1) and anorectal D1 and compared between the two approaches (Wilcoxon signed rank, α = 0.05).