ESTRO 2025 - Abstract Book

S2930

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

ESTRO 2025

PENELOPE, in contrast, provided more consistent estimates at low energies. These differences emphasize the importance of choosing the appropriate Monte Carlo code based on the energy range and study objectives.

Keywords: Simulations, Monte Carlo, Cell survival

References: [1] V.A. Semenenko, R.D. Stewart. Fast MC simulation of DNA damage by electrons and ions. Phys Med Biol , 51(7):1693, 2006. [2] R.D. Stewart, V.K. Yu, A.G. Georgakilas et al. Effects of radiation quality on clustered DNA lesions. Radiat Res , 176(5):587–602, 2011. [3] W. Wang, C. Li, R. Qiu et al. Modelling cellular survival after DNA DSBs. Sci Rep , 8(1):16202, 2018. [4] S.M. Sebastián et al. MC of cell survival in proton SOBP. Phys Med Biol , 68(19):195024, 2023. [5] C.M. De Lara et al. Yield of DNA DSBs in hamster V79 cells with ultrasoft X-rays. Radiat Res , 155(3):440–448, 2001.

[6] C. Ahdida et al. New capabilities of FLUKA code. Front Phys , 9:788253, 2022. [8] Data Bank. PENELOPE: MC simulation of electron and photon transport, 2015.

4341

Digital Poster Method for in vivo dosimetry in head and neck treatments Antonio De Donato, Francesca Greco, Maria Antonietta Gambacorta, Nicola Dinapoli, Mariangela Massaccesi, Matteo Galetto, Vincenzo Frascino, Stefania Teodoli, Gerardina Stimato, Marco De Spirito Dipartimento Diagnostica per Immagini e Radioterapia Oncologica, Policlinico Universitario Agostino Gemelli, Roma, Italy Purpose/Objective: This study evaluates the accuracy and reliability of In Vivo Dosimetry (IVD) as a tool for monitoring the dose delivered in head and neck radiotherapy. The research uses an IVD system (SunCHECK, SunNuclear) based on an EPID (Electronic Portal Imaging Device). The measured dose is compared with the reference calculated dose using Gamma Index analysis. The goal is to define a Gamma Index analysis criterion that provides clinicians with an accurate method to determine the personalized timing for treatment replanning based on anatomical changes. Material/Methods: The IVD system, using the a-Si 1200 EPID and forward-projection dosimetry, measures 2D dose distributions to detect anatomical changes during head and neck treatments. Patients are immobilized with thermoplastic masks, and setups are verified daily via Image Guided Radiotherapy IGRT. The software calculates the expected dose and compares it to the measured dose using Gamma Index analysis (Distance to Agreement (DTA): 7 mm, D%: 3%, pass rate: >95%). To assess dosimetric variations, MIM Maestro® generates a synthetic CT from CBCT, transferring clinical ROIs via image registration. This synthetic CT enables recalculating 3D doses using Eclipse™ TPS, verifying PTV coverage (95%) and OAR dose limits. Results are correlated with 2D IVD evaluations for treatment adjustments. Results: Nineteen patients were divided into three groups. For the first group, the in vivo dosimetry system showed Gamma passing rate values above 97% (98.6% ±0.7%) for all treatment fractions. In the second group, some fractions had values below 97%, but no replanning was done. The third group required replanning. In the second group, Gamma passing rates dropped below 94% after the thirtieth fraction, starting from 99.2% for the first fraction and decreasing to 91.3% for the thirty-fifth. In the replanning group, values decreased until the nineteenth fraction (99.5% to 93.4%) but recovered to 98.5% after replanning. Target coverage remained stable for the first group, while it decreased for the second and third groups as measured and calculated dose differences increased.