ESTRO 2025 - Abstract Book

S2637

Physics - Detectors, dose measurement and phantoms

ESTRO 2025

Purpose/Objective: For specific entities, carbon-ion beams are preferred over conventional photon beams due to their inverse dose profile and higher radiobiological effectiveness [1]. Due to scarce data, the current uncertainty of the beam quality correction factor k Q for carbon-ion beams remains large at 2.4% [2]. A recent study derived k Q in carbon-ion beams using Monte Carlo simulations and showed a deviation to measured k Q exceeding the simulation uncertainty of 1.7% [3,4]. In this work, Monte Carlo calculations of k Q were performed using GATE/Geant4 and FLUKA. These values were validated for monoenergetic carbon-ion beams using cross-calibration measurements at a synchrotron-based facility. Material/Methods: The Monte Carlo software package GATE (version 9.3) /Geant4 (version 11.1.2), as well as FLUKA (version 2021.2.9) were used in this study to calculate k Q for two plane-parallel (PTW 34001 and PTW 34045) as well as two farmer-type (PTW 30013 and IBA FC65-G) ionization chambers. Cross-calibration measurements have been performed at a synchrotron-based facility using the same chambers for monoenergetic carbon-ion beams with initial beam energies of 278 MeV/u and 430 MeV/u with a field size of 6x6 cm 2 at a depth of 5 cm. The values of the PTW 30013 chamber were used as the reference for the calculation of k Q ratios. All measurements were corrected for saturation and polarity effects. Results: The simulated and measured k Q ratios from this study for all investigated chambers agree within 1.4% as presented in Figure 1. The results also agree with those derived from literature [3,4], with a maximum deviation of 0.8%, except for PTW34001 chamber, which had a deviation of 1.8% for the initial beam energy of 429 MeV/u. Nevertheless, considering the measurement and simulation uncertainty, this observed difference cannot be considered statistically significant.

Figure 1: Simulated and measured k Q ratios against the k Q of a PTW 30013 chamber for three chambers, using monoenergetic carbon-ion beams of 278 MeV/u and 429 MeV/u, compared with the results from [3,4].

Conclusion: The results demonstrated consistency between the simulated and measured k Q ratios. Both the used Monte Carlo codes show a maximum discrepancy of 0.8%. The larger discrepancy between our results and the literature for the PTW 34001 chamber at 429 MeV/u deserves further investigations.