Interlaboratory comparison of two homemade pencil type ionization chambers

Computed tomography (CT) is a diagnostic exam responsible for the highest dose values received by the patients during the procedure. Over the years, this kind of equipment has been improved to ensure that the patients do not receive unnecessary doses. For this reason it is important to keep a quality control program for the CT equipment. To perform the dosimetry in CT beams, the instrument used is usually a pencil type ionization chamber with a sensitive volume length of 10 cm. However, this kind of detector is available with different sensitive volume lengths. The aim of this study was to compare the response of two homemade pencil type ionization chambers with sensitive volume lengths of 10 cm and 30 cm in the laboratories of Instituto de Pesquisas Energéticas e Nucleares (IPEN, Brazil) and National Physical Laboratory (NPL, UK). The characterization tests were performed, and the results obtained are within the international recommended limits. The only difference observed in the response of the two chambers in both laboratories is the fact that the ionization current obtained in all the tests at the IPEN is higher than at the NPL, because of the beam characteristics.