Dosimetric performance of the new PTW 31022 PinPoint 3D ionization chamber in high energy photon beams

Abstract

This paper is an investigation of the dosimetric performances of the new PTW T31022 PinPoint 3D which supersedes T31016. Measurements have been performed in small and large fields conditions, with (WFF) and without flattening filter (FFF) for two energies. The study includes characterization of ion collection efficiency (Jaffé plots), polarity effect and measurements of beam profiles, depth dose curves and output factors associated to small field correction factors. The T31022 Jaffé plots were found to be more linear than those of the T31016 and the use of the two-voltage technique was validated. The use of the chamber in small fields (≤1 × 1 cm2) leads to an underestimation of output factors but presents lower field output correction factors than its predecessor. The chamber was found to present a field size dependence of the polarity correction factor (<1%). This polarity effect is particular notable when measuring a depth dose curve of a 40 × 40 cm2 field and 6WFF photon beams.