ESTRO 2025 - Abstract Book

S2841

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2025

2902

Digital Poster Dosimetric evaluation of helical tomotherapy and non-coplanar dual arcs VMAT for hippocampal-avoidance prophylactic cranial irradiation (HA-PCI) Aïcha Traore-Diallo 1 , Agathe Vatonne 1 , Angela Botticella 1 , Luiza Souza 2 , Corinne Faivre-Finn 3 , Cécile Le Péchoux 1 , Antonin Levy 1,4 1 Radiation Oncology, Gustave Roussy, Villejuif, France. 2 EORTC HQ, EORTC, Brussels, Belgium. 3 3. The Christie NHS Foundation Trust, University of Manchester, Manchester, United Kingdom. 4 3. Faculté de Médecine, Université Paris Saclay, Le Kremlin-, France Purpose/Objective: HA-PCI has the potential to reduce neurotoxicity compared to conventional PCI, but its implementation in daily practice presents technically challenging. This study compares the dosimetry performance of two commonly used techniques for HA-PCI: Helical Tomotherapy (HT) and non-coplanar dual arcs volumetric-modulated arc therapy (VMAT). Material/Methods: HT and VMAT treatment plans were generated to deliver a dose of 25 Gy/10 fractions to the planning target volume (PTV_2500) for the same five patients undergoing HA-PCI. The hippocampi and other critical organs were delineated on brain MRI fused with CT planning images. A 5mm outward expansion of the hippocampi was created to form the planning organ at risk volume (PRV hippocampi). Dose constraints from the PRIMALung (EORTC-1901) trial [1] were applied: D98% ≥95% for PTV_2500, D98% <8.5 Gy, and D0.03cc <15.0 Gy for the hippocampi. Dosimetric parameters were assessed using Volo Ultra Planning with Accuray Precision® for HT and Raystation® for VMAT. VMAT treatments were delivered on an Elekta® linear accelerator equipped with Brainlab Exactrac® dynamic image guidance system. HT treatments were delivered on a TOMOTHERAPY® TomoHD™ SYSTEM. The Mann-Whitney test was used to compare quantitative variables. Results: Both techniques showed no significant differences in PTV_2500 coverage (D98%: 22.98 ± 0.38 Gy for HT vs. 22.62 ± 0.78 Gy for VMAT; p = 0.6) and hippocampi D98% (7.27 ± 0.08 Gy for HT vs. 7.17 ± 0.22 Gy for VMAT; p = 0.6). However, the PRV hippocampi D98% was significantly lower with VMAT (8.26 ± 0.12 Gy for HT vs. 7.59 ± 0.21 Gy for VMAT; p = 0.008). The maximum delivered dose (D0.03cc) to the hippocampi was also lower with VMAT (13.30 ± 0.10 Gy for HT vs. 13.18 ± 0.06 Gy for VMAT; p = 0.043). There was no significant difference in the PRV hippocampi D0.03cc (22.45 ± 1.14 Gy for HT vs. 22.72 ± 0.45 Gy for VMAT; p = 0.25) or optic nerves, chiasm, and lens D0.3cc. Conclusion: The dosimetric results favour VMAT, demonstrating lower hippocampi D0.03cc and PRV hippocampi D98% compared to HT. Additionally, VMAT potentially offers the advantage of a shorter treatment time. However, these findings require validation in a larger cohort for further validation to confirm their robustness and clinical significance.

Keywords: IMRT, VMAT, SCLC, hipocampal-sparing PCI

References: 1. Levy A, Berghmans T, Koller M, et al. PRIMALung (EORTC-1901): PRophylactic cerebral Irradiation (PCI) or active brain MAgnetic resonance imaging (MRI) surveillance in small-cell Lung cancer (SCLC) patients. Lung Cancer. 2024 Oct 24;198:107993