ESTRO 2025 - Abstract Book

S2675

Physics - Detectors, dose measurement and phantoms

ESTRO 2025

Conclusion This study has partially characterized the two instruments for pre-treatment dosimetry in stereotactic radiotherapy. Although both demonstrate good performance in sensitivity and reproducibility, it was found that, especially in intensity-modulated treatments, dosimetric accuracy can be influenced by operational variables, such as treatment geometry.

Keywords: SRS MapCHECK, Portal Dosimetry, Г test

References Ahmed, S., Zhang, G., Moros, E. G., & Feygelman, V. (2019). Comprehensive evaluation of the high-resolution diode array for SRS dosimetry. Journal of applied clinical medical physics , 20 (10), 13–23. https://doi.org/10.1002/acm2.12696

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Digital Poster Determination of beam quality correction factors for alanine dosimeters in monoenergetic and modulated 12C-ion beams Pascal Saße 1 , Jessica Stolzenberg 2,3 , Kilian Baumann 2,3,4 , Ralf-Peter Kapsch 5 , Hugo Palmans 6,7 , Björn Poppe 1 , Hui Khee Looe 1 1 University Clinic for Medical Radiation Physics, Carl von Ossietzky University, Oldenburg, Germany. 2 Department of Radiotherapy, University Hospital Gießen-Marburg, Marburg, Germany. 3 Institute of Medical Physics and Radiation Protection, University of Applied Sciences, Gießen, Germany. 4 Medical Physics, Marburg Ion-Beam Therapy Center, Marburg, Germany. 5 Ionizing Radiation, Physikalisch-Technische Bundesanstalt, Braunschweig, Germany. 6 Acoustics and Ionising Radiation Division, National Physical Laboratory, Teddington, United Kingdom. 7 Medical Physics, MedAustron Ion Therapy Center, Wiene Neustadt, Austria Purpose/Objective The uncertainty of dosimetry with air-filled ionization chambers in light ion beams, such as 12 C-ion, remains higher than conventional photon beams, mainly attributed to the higher uncertainty associated with the beam quality correction factor k Q,Q0 . Calibrated alanine dosimeters have also been frequently used in particle beams as promising alternatives to ionization chambers. To account for their LET-dependent response, this work aims to derive the k Q,Q0 for alanine dosimeters in clinical monoenergetic and modulated 12 C-ion beams.

Material/Methods The k Q,Q0 for alanine dosimeter can be expressed as:

where Q 0 is the calibration beam quality. The dose-weighted average of the relative effectiveness was computed from the spectral fluence of all ions. Alanine response data for different projectiles was provided by [1]. Simulations were performed using GATE v9.3 and Geant4 v11.2.2. were obtained at 5 cm depth for two monoenergetic 278 and 429 MeV/u 12 C-ion beams and a modulated beam (see Figure 1). For the latter, in every 1 cm within the SOBP was scored additionally. The alanine collision-stopping powers were obtained using SRIM [2]. Water-to-alanine stopping power ratios were calculated from the simulated and the respective stopping powers. The dose weighed stopping power ratios for 60 Co was taken from [3]. Measurements were performed for the two monoenergetic beams. For each measurement, five alanine pellets were placed in a solid phantom at a water-equivalent depth of 5 cm within a corresponding holder. Each pellet was