Determination of the sensitive volume of the PTW N23361 ionization chamber by micro-computed tomography

The determination of the sensitive volume of ionization chambers is essential to ensure the best possible accuracy in dosimetric procedures, especially in the context of radiotherapy and radiation protection. This work presents a geometric analysis of the ionization chamber manufactured by PTW, model N23361, whose nominal volume is 30 cm³ as declared by the manufacturer. The three-dimensional reconstruction was performed using images obtained through micro-computed tomography (micro-CT) with the Baker Hughes GE Phoenix V|tome|x M300 system, enabling detailed internal visualization and precise segmentation of the sensitive cavity, with the complete exclusion of the central electrode. The determined volume was 30.7 cm³, revealing a difference of +0.7 cm³ (+2.3%) in relation to the value provided by the manufacturer. The use of micro-CT proved to be an effective metrological tool for the non-destructive evaluation of ionizing radiation measurement devices, allowing for more accurate analyses than conventional methods. This study is part of a broader initiative aimed at implementing a primary air-kerma standard at the Department of Radiological Sciences (DCR).