ESTRO 2025 - Abstract Book

S2706

Physics - Dose calculation algorithms

ESTRO 2025

Conclusion: The introduction of the ELM (Enhanced Leaf Model) in version 18 of the Acuros dose calculation algorithm represents a significant advancement in the accuracy of dosimetric calculations for the 6 MV beam generated by the Varian Clinac iX linear accelerator. Validation of the data through machine measurements, including profiles, PDDs, and diagonals, as well as the comparison of discrepancies between TPS results and measurements, confirms the effectiveness and robustness of this update. Additional tests on electron contamination, energy spectrum, backscatter factor, and mean radial energy demonstrate a notable improvement in beam modeling. These results validate the application of the ELM module in radiotherapy treatment planning and strengthen the reliability of calculations performed with this new configuration.

Keywords: dose calculation , enhanced leaf model , acurosXB

References: Testing of an enhanced leaf model for improved dose calculation in a commercial treatment planning system , DOI: 10.1002/mp.16019 Eclipse Photon and Electron Algorithms Reference for varian GuideP1053284-001-A Vieillevigne L, Khamphan C, Saez J, Hernandez V. On the need for tuning the dosimetric leaf gap for stereotactic treatment plans in the Eclipse treatment planning system. J Appl Clin Med Phys. 2019;20(7):68-77. https://doi.org/10.1002/acm2.12656

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Digital Poster Establishing an in vivo dosimetry for breast radiotherapy treatments using SunCHECK PerFRACTION João Gaspar 1 , Fábio Alves 1 , Ana Oliveira 1 , Liliana Conceição 1 , Filipa Carvalho 1 , Mary Araújo 1 , Fernanda Rocha 1 , Maria José Pereira 2 , Diana Sousa 2 , Ana Célia Louro 2 , Maria Pires 3 , Tiago Ventura 1 , Josefina Mateus 1 , Maria do Carmo Lopes 1 1 Física Médica, IPOC, Coimbra, Portugal. 2 Radioterapia, IPOC, Coimbra, Portugal. 3 Física, FCTUC, Coimbra, Portugal Purpose/Objective: A post-commissioning retrospective study was conducted to analyse SunCHECK TM PerFRACTION data and establish a clinical routine protocol for breast radiotherapy treatments. Material/Methods: The study included 2D-images from 250 breast cancer patients treated on a TrueBeam STX TM linac between November 2023 to September 2024. A total of 5151 2D-images were acquired using the MV Imager aS1200 during the first five fractions for each patient and processed in the SunCHECK TM PerFRACTION platform. Breast irradiations using 3DCRT, VMAT and Hybrid VMAT techniques included cases with or without lymph node regions, and with or without SIB. All images were assessed using global gamma analysis criteria of 5%/3mm and a 10% threshold, with a passing rate of over 90%. Fractions with failed images were subject to offline review (ECLIPSE TM v16.1) to provide an independent evaluation method to help identify the causes of failures. Results: A total of 28% of patients had at least one image in one or more fractions that did not meet the gamma criteria, representing 6% (325 images) of all analysed images. 253 of those failed images (78%) were classified as true positives, while 22% (72 images) as false positives. The true positives were registered for 50% (126 images) of the cases observed for 3DCRT breast irradiation, 46% (116 images) for VMAT node irradiation and 4% (11 images) for VMAT breast irradiation. The main identified failure causes were positioning and anatomy changes. The false positives cases were assigned to flat panel calibration limitations, treatment interruption and unknown factors.