Application of the correction factor for radiation quality Kq in dosimetry with pencil-type ionization chambers using a tandem system

Abstract

The pencil-type ionization chamber widely used in computed tomography (CT) dosimetry, is a measuring instrument that has a cylindrical shape and provides uniform response independent of the angle of incidence of ionizing radiation. Calibration and measurements performed with the pencil-type ionization chamber are done in terms of Kerma product in air-length (Pk,l) and values are given in Gy.cm. To obtain the values of (Pk,l) during clinical measurements, the readings performed with the ionization chamber are multiplied by the calibration coefficient (Nk,l) and the correction factor C for quality (Kq) which are given in Calibration certificates of the chambers. The application of the correction factor for radiation quality Kq is done as a function of the effective energy of the beam that is determined by the Half Value layer (HVL) calculation. In order to estimate the HVL values in this work, a Tandem system made up of cylindrical aluminum and PMMA absorber layers was used as a low cost and easy to apply method. From the Tandem curve, it was possible to construct the calibration curve and obtain the appropriate Kq to the beam of the computed tomography equipment studied.