ESTRO 2024 - Abstract Book

S3314

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

2239

Poster Discussion

Monte Carlo calculations of beam quality correction factors for monoenergetic carbon-ion beams

Jessica Stolzenberg 1 , Pascal Saße 1 , Kilian Baumann 2,3,4 , Björn Poppe 1 , Hui Khee Looe 1

1 University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University, Oldenburg, Germany. 2 University Hospital Gießen-Marburg, Department for Radiotherapy, Marburg, Germany. 3 University of Applied Sciences, Institute of Medical Physics and Radiation Protection, Gießen, Germany. 4 Marburg Ion-Beam Therapy Center, MIT, Marburg, Germany

Purpose/Objective:

Heavy ions such as carbon-ions are considered to possess higher clinical potential in radiation therapy compared to photon beams regarding their higher biological effectiveness and distinct Bragg-peak towards the end of their range. For the reference-dosimetry of carbon-ion beams, the beam quality correction factor ( k Q ) is still associated with uncertainties of approximately 3% [1]. Compared to this, the uncertainty of k Q for photon beams is below 1% [2]. The higher uncertainty of the k Q factor for carbon-ion beams is a result of scarce data in the literature. As in the case of therapeutic photon beams, more comprehensive Monte Carlo studies can help to close this gap. Therefore, the goal of this study is to calculate k Q factors for ionization chambers using Monte-Carlo simulations. To ensure good comparability, the simulation conditions have been designed in accordance with the experimental studies conducted previously (Holm [3] and Blättermann [1]), where the k Q factors have been determined directly using calorimetry measurements as the reference. The Monte Carlo software package GATE (version 9.3)/Geant4 (version 11.1.2) was used in this study. Firstly, the differences between the eight available ready-to-use nuclear physics lists in modeling the nuclear interactions for the application of carbon-ion beams have been investigated. For all investigated lists, the ElectromagneticOption4 has been used that best represents electromagnetic physics models and parameters [4]. For this purpose, depth dose distributions were simulated using all physics lists for a monoenergetic carbon-ion beam with an initial energy of 429 MeV/u. Additionally, the influence of four selected physics lists on the k Q factors for a cylindrical air-filled ionization chamber (Type 30013, PTW Freiburg) was studied. In the second step, the k Q factors have been simulated for the PTW 30013 chamber and the Roos parallel-plate chamber (34001, PTW Freiburg) using one selected physics list. In these simulations, two initial beam energies of 278.29 MeV/u and 429 MeV/u have been investigated. Additionally, the individual perturbation factors p Q,i for the PTW 30013 with the initial beam energy of 278.29 MeV/u have been simulated. For all simulations, the reference point of the ionization chambers was placed at a measurement depth of 5cm in water. Material/Methods:

Results: