Feasibility study of glass dosimeter for postal dose intercomparison of high-energy proton therapy beams

Abstract

PurposeWe evaluated the glass dosimeter suitability as an external audit program in proton therapy beam. A feasibility test of the glass dosimeter postal dose intercomparison was performed for high-energy proton beam use in radiation oncology with the collaboration of five proton therapy centers (Shizuoka Cancer Center, University of Florida Proton Center, MD Anderson Cancer Center, Loma Linda University Medical Center, and University of Pennsylvania School of Medicine). Material and methodsThe dosimetric properties of a GD-301 glass dosimeter were investigated for its potential use for postal dosimetry. Measurements were performed in a water phantom using a stair-like holder specially designed for this study. The depth-dose distribution measured with the glass dosimeter was compared to those from GEANT4 Monte-Carlo simulation. The GEANT4 code was also used to simulate the influence of holder material in the absorbed dose by inserting the glass dosimeter in a water phantom within the stair-like holder. We investigated the methodology of the absorbed dose determination with the glass dosimeter system establishing the calibration factor and various correction factors (non-linearity, fading, energy, holder). The participating proton therapy centers were asked to irradiate the glass dosimeter to 2 Gy with similar setup and conditions. ResultsThe repeatability and dose rate dependence is within 1.2% and 1.5%, respectively. Depth-dose distributions in the pristine Bragg curve and the spread-out Bragg curve were estimated to be within 3%, compared with depth-dose measured with the ionization chamber. The difference in absorbed dose between the glass dosimeter and ionization chamber was within ±2% as a function of proton beam quality, residual ranges were between 2.1 and 9.0 cm. The influence of the holder material in absorbed doses of the proton beams is less than 1%. In the accuracy evaluation of the glass dosimeter system established in blind test, we obtained within 2.5% agreements with the ionization chamber dosimetry for the proton beam. In this feasibility study, the results on the proton beam output check are relatively good within ±6% for all participating centers. ConclusionWe believe that the glass dosimeter system has considerable potential to be used for a postal dose audit program in proton beam.