A cross-validation study of Ge-doped silica optical fibres and TLD-100 systems for high energy photon dosimetry audit under non-reference conditions

Abstract

This study compares the practicality of Ge-doped silica optical fibres as a potential remote dosimeter for radiotherapy postal dosimetry audit in non-reference conditions with a commercial thermoluminescence dosimeter (TLD-100). The optical fibre system consists of two types of fibres: cylindrical (CF) and flat fibres (FF). The dosimetric characteristics of the systems were investigated and compared, with particular attention to dose linearity, energy dependence, reproducibility, and fading. Measurements of absorbed doses of CF, FF, and TLD-100 were made, along with uncertainty budgets. A preliminary test was performed under non-reference conditions to evaluate the variations in absorbed doses measured with CF and FF versus TLD-100. For both 6 MV and 10 MV photon beams, CF, FF, and TLD-100 show a linear dose-response from 1 Gy to 3 Gy with a coefficient of determination (R2) greater than 0.99, minimal energy dependence, and good reproducibility with less than 3% deviation. The highest fading rates were 37.6%, 63.4%, and 14.2% for CF, FF, and TLD-100, respectively, at day 106 after irradiation. For irradiation with a photon beam of 6 MV, the combined relative standard uncertainty of absorbed dose determined from CF, FF, and TLD-100 measurements was estimated to be 4.3%, 5.56%, and 0.74%, respectively. Preliminary absorbed dose measurement tests under non-reference conditions showed that the mean ratios of Ge-doped silica optical fibres to TLD-100 for on-axis dose, wedge transmission, and output factor were 1.014, 0.991, and 1.013, respectively. The Ge-doped silica optical fibre systems have dosimetric performance commensurate with the TLD-100 and can be used as a potential remote dosimeter for mailed dosimetry audits if appropriate correction factors are applied to the absorbed dose measurements.