S1862
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
single irradiation, whose magnitude deserves attention. Although these doses are deposited under UHDR conditions, they still need investigation, as it remains unclear whether they produce the same protective effect, and their long-term biological consequences remain unknown.For this reason, this work presents a preliminary evaluation of peripheral dose in virtual treatments using a UHDR accelerator and Monte Carlo simulation. Material/Methods: A SIT electronFlash accelerator has been characterized at 9MeV for circular applicators ranging from 10 to 120 mm using a PTW MP3-P water phantom and a flashDiamond detector. Monte Carlo simulations were performed with GAMOS/Geant4, to study the out-of- field dose distributions generated during 9 MeV electron irradiations. The simulations included a detailed model of the LINAC for different applicators, a voxelized anthropomorphic phantom based on the ICRP-110 standard and all inside of a bunker, without the treatment couch.Two virtual treatment cases were simulated: one located in the right leg, 10 cm above the knee, and another in the right chest wall of the lung, below the axilla, each with a prescribed dose of 15 Gy.Monte Carlo simulations were performed until they achieved an uncertainty below 3% for voxels receiving at least 1 mGy and less than 0.5 % for 10 mGy.
Conclusion: This work successfully developed VektraMC, a Monte Carlo model of the small-head Vektra Electronic Brachytherapy system. X-ray spectra were generated for all available tube potentials. These results will be validated with measurements in 2026, forming the foundation for incorporating the Monte Carlo dosimetry model into the Vektra treatment planning system. References: [1] D. Bartowski. Vektra physics overview. 2025.[2] D. Badali, G. Plateau, C. Ellenor, C-Y. Ku, P. Vatahov, J. Esterline, B. Wilfley, C. Mitchell, K. Fishman,and T. Funk. Characterization of an x-ray source with a partitioned diamond tungsten target for electronic brachytherapy with 3d beam directionality. Physics in Medicine and Biology, 2019.[3] C.M. Poole, I. Cornelius, J.V. Trapp, and C.M. Langto. A cad interface for geant4. Australas Phys Eng Sci Med, 2012. Keywords: electronic brachytherapy, Monte Carlo An approach to the assessment of peripheral dose in ultra-high dose rate electron treatments by Monte Carlo simulations Itsaso Pérez-Ilzarbe 1 , Juan Ignacio Lagares 2 , Pedro Arce 2 , Francisco Sánchez-Doblado 3 , Marta Ibañez- Moragues 2 , Miguel Ángel Morcillo 2 1 Faculty of Sciences, Universidad de Alcalá, Alcalá de Henares, Spain. 2 Technology, CIEMAT, Madrid, Spain. 3 Faculty of Medicine, Universidad de Sevilla, Madrid, Spain Purpose/Objective: Ultra-High Dose Rate (UHDR) treatments, aimed at achieving the FLASH effect, appear to require a single irradiation delivering a therapeutic-level dose in one fraction. This also implies higher peripheral doses in a Digital Poster 1948
Results: Analysis of the mean absorbed dose in the simulated treatment showed that skin and other organs near the treatment field can receive doses of several grays
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