Characterization of a commercial PIN diode for radiotherapy photon beam dosimetry

Abstract

The dosimetric characterization of a commercial diode (BPW-34) was performed using a True Beam accelerator (Varian), with flattening filter (FF) photon beams of 6 and 15 MV and flattening filter free (FFF) of 6 MVFFF. The main performance characteristics, namely dose response, energy and dose rate dependence, field output factor, and percentage depth dose profile (PDD), were compared with those available in the literature and, whenever possible, benchmarked against the Varian Eclipse treatment planning system (TPS) predictions. Regardless of the energy, the results showed that the dose response curves are linear (R2 = 1) with nonlinearity parameters less than 0.1% and 0.3% of repeatability. Furthermore, the average dose rate effect (0.7%) is almost negligible within the range of 20–600 MU/min (6 MV, 15 MV) and 400–1400 MU/min (6 MVFFF). Despite these good results, the charge sensitivity measurements evidenced that the diode response depends slightly on the energy, being within 5% for 6 MV–15 MV. It is important to underline that all these results adhere to the standard radiotherapy dosimetry protocols. Moreover, the general output field factor measurements and the percentage depth dose profiles, which are in excellent agreement with the Eclipse TPS calculations, also demonstrated that the diode BPW-34 is a low-budget alternative radiotherapy photon beam dosimeter.