Open AccessWater calorimetry-based k Q factors for Farmer-type ionization chambers in the SOBP of a carbon-ion beam
Author(s) -
K. Holm,
Oliver Jäkel,
A. Krauss
Publication year - 2021
Publication title -
physics in medicine and biology/physics in medicine and biology
Language(s) - English
Resource type - Journals
eISSN - 1361-6560
pISSN - 0031-9155
DOI - 10.1088/1361-6560/ac0d0d
Subject(s) - sobp , ionization chamber , calorimeter (particle physics) , calibration , beam (structure) , dosimetry , bragg peak , ion , ionization , absorbed dose , materials science , photon , measurement uncertainty , atomic physics , nuclear physics , computational physics , irradiation , physics , optics , detector , nuclear medicine , medicine , quantum mechanics
The dosimetry of carbon-ion beams based on calibrated ionization chambers (ICs) still shows a significantly higher uncertainty compared to high-energy photon beams, a fact influenced mainly by the uncertainty of the correction factor for the beam quality k Q . Due to a lack of experimental data, k Q factors in carbon-ion beams used today are based on theoretical calculations whose standard uncertainty is three times higher than that of photon beams. To reduce their uncertainty, in this work, k Q factors for two ICs were determined experimentally by means of water calorimetry for the spread-out Bragg peak of a carbon-ion beam, these factors are presented here for the first time. To this end, the absorbed dose to water in the 12 C-SOBP is measured using the water calorimeter developed at Physikalisch-Technische Bundesanstalt, allowing a direct calibration of the ICs used (PTW 30013 and IBA FC65G) and thereby an experimental determination of the chamber-specific k Q factors. Based on a detailed characterization of the irradiation field, correction factors for several effects that influence calorimetric and ionometric measurements were determined. Their contribution to an overall uncertainty budget of the final k Q factors was determined, leading to a standard uncertainty for k Q of 0.69%, which means a reduction by a factor of three compared to the theoretically calculated values. The experimentally determined values were expressed in accordance with TRS-398 and DIN 6801-1 and compared to the values given there. A maximum deviation of 2.3% was found between the experiment and the literature.