ESTRO 2024 - Abstract Book

S3408

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

The physical properties of 3D-printed boluses depend on filling density. To keep the difference between 3D prints and commercially available solutions below the measurement error (0,5%) filling of 80% and 100% density should be chosen. We found no clinically significant differences in elastic boluses depending on the degree of flexibility. Our study confirms the safety of using flexible boluses in radiation oncology.

Keywords: 3D boluses, filling density, materials

3225

Digital Poster

Commissioning of the Fricke solution dosimeter for particle therapy

Charlotte Breitenbach 1 , Larissa Derksen 2 , David Weishaar 2 , Robin Erdmann 2 , Klemes Zink 2,3,4 , Sebastian Adeberg 3,4 , Ulrike Theiss 3 , Kilian-Simon Baumann 2,3,4 1 Philipps-University of Marburg, Physics, Marburg, Germany. 2 University of Applied Science, Institute of Medical Physics and Radiation Protection, Giessen, Germany. 3 University Medical Center Giessen-Marburg, Department of Radiotherapy and Radiooncology, Marburg, Germany. 4 Marburg Ion-Beam Therapy Center, Medical physics, Marburg, Germany

Purpose/Objective:

In radiotherapy, accurate dose delivery and thus clinical dosimetry is of great importance. In addition to the widely used ionization chambers, chemical dosimeters such as the Fricke solution were used for photon dosimetry in the 1970s. To the best of our knowledge, the Fricke solution has not yet been used in particle therapy. In order to investigate the Fricke solution for particle therapy in more detail and to compare it with Monte Carlo simulations, the LET-dependence of the Fricke solution was investigated in this study.

Material/Methods:

The FRICKE solution is an aqueous sulfuric acid solution containing Fe(II)-ions. Under irradiation, irreversible oxidation of the ferrous ions to ferric ions occurs, changing the optical density of the solution in the UV range. The number of ferric ions created per 100 eV deposited energy is described by the G-value and is proportional to the dose. In this work, the dependence of the FRICKE solution's response on the LET is investigated. For this purpose, experiments were performed at Marburg Ion-Beam Therapy Center with carbon ions at energies of 430 MeV/u and 149 MeV/u. In addition, protons with energies of 80 MeV/u and 221 MeV/u and photons with 6 MV-X were investigated. The extinction of the irradiated solutions was read out with a photometer at 304 nm. From the slope of the linear response of the FRICKE solution the G-value was derived. Additionally, Monte Carlo simulations with the toolkit TOPAS-nBio based on the Monte Carlo code Geant4 were performed to calculate the G-value of Fe(III)-ions under the same conditions as employed in the experiments. Additionally, the response of the FRICKE solutions was calculated at two different depth of a modulated carbon ion beam: 1) at the entrance channel and 2) at the region of the spread-out Bragg peak.