Direct determination offor Farmer-type ionization chambers in a clinical scanned carbon-ion beam using water calorimetry.

Within two studies,factors for two Farmer-type ionization chambers have been experimentally determined by means of water calorimetry in the entrance channel (EC) of a monoenergetic carbon-ion beam (Osinga-Blättermann20172033-54) and for a passively modulated spread-out Bragg peak (SOBP) (Holm2021145012). Both studies were performed at the Heidelberg Ion Beam Therapy Center (HIT) using the PTB portable water calorimeter but applying different initial beam energies of 429 MeV ufor the EC and 278 MeV ufor the SOBP as well as different scanning patterns of the irradiated field. Comparing their results revealed differences between the experimentalfactors of up to 1.9% between the EC and the SOBP. To further investigate this unexpected difference, we performed additionaldeterminations for the EC of an 278 MeV umonoenergetic carbon-ion beam and reevaluated the original data of Osinga-Blättermann(20172033-54). This new experimental data indicated no difference between thefactors for the EC and the SOBP and the reevaluation led to a substantial reduction of the originally publishedfactors for the EC of the 429 MeV ubeam (Osinga-Blättermann2017.2033-54). Finally, no significant difference between the data for the EC and the data for the SOBP can be found within the standard measurement uncertainty of experimentalfactors of 0.8%. The results presented here are intended to correct and replace thedata published by Osinga-Blättermann(2017.2033-54) and in Osinga-Blättermann and Krauss (2018015009).