Performance Evaluation of a Transmission Reference Detector for Commissioning Beam Data in a Wedge Field

Abstract

The purpose of this study is to evaluate the performance of a “stealth chamber” as a novel reference detector for measuring the commissioning beam data for a wedge field. The stealth chamber is a transmission ionization chamber intended to be used as a reference chamber for relative dosimetry. The percentage depth doses (PDDs) and the dose profiles of 6-, 8-, and 10-MV photon beams of four wedge filters were measured using the stealth and the CC13 chambers as reference detectors. The PDD and the profile measurements were performed under various field sizes ranging from 4 × 4 cm2 to 20 × 20 cm2. For the evaluate of the performance of the stealth chamber in fields with a physical wedge, all measurement data obtained using the stealth chamber as a reference detector were compared with those measured using two CC13 chambers as both field and reference detectors. For the PDDs, the differences in dosimetric parameters such as the depth of maximum dose (dmax) and the PDD at 10 cm (D10) and 5 cm (D5) were analyzed for both reference detectors. In addition, the root-mean-square error (RMSE) was calculated to measure the agreement of the profiles at dmax and a 10 cm depth. The percentage differences in D10 and D5 between both detectors were less than 1% for all energies and fields with four wedges. Furthermore, the RMSEs of the profiles at dmax and 10-cm depth in both chambers were within 1% for all energies and fields except for the 60° wedge angle. This study found that the use of a stealth chamber to measure the commissioning beam data for a wedge field is feasible, although a relatively large difference in the PDD was observed in the build-up region. However, we recommend careful verification of the PDDs and dose profiles for large field size and wedge angle before clinical use.