Characterization of three solid state dosimetry systems for use in high energy photon dosimetry audits in radiotherapy. (November 2017) - Wesolowska, Paulina Elzbieta
Abstract: The IAEA Dosimetry Laboratory (DOL) aims to improve the accuracy of clinical dosimetry in hospitals world-wide by providing independent remote audits for high energy photon beams. A thermoluminescent dosimetry (TLD) system has been used by the DOL to provide audit services for over 47 years. Two additional systems: an optically stimulated luminescent dosimetry (OSLD) system and a radiophoto luminescent dosimetry (RPLD) system underwent a commissioning process. The systems' parameters, reading methodology and the dosimetric characteristics were investigated and compared. The read-out procedure for each system was established and optimized. Dosimetric characteristics such as reproducibility, signal fading with time after irradiation, signal per dose dependence and energy response were investigated. Additional tests to check signal depletion per readout and individual sensitivities of dosimeters were performed for RPLDs and OSLDs and also reading position dependence for the RPLD system was checked. The reproducibility of 4 readings of one dosimeter is 0.48% for TLDs, 0.16% for OSLDs and 0.15% for RPLDs. The fading effect after 100 days was 4% for TLD, 2% for OSLD and 0.4% for RPLD. Energy response of TLDs and RPLDs is comparable, higher corrections were found for OSLDs. The RPLD dose-response is sub-linear whereas TLD and OSLD response is supra-linear at the dose range under study (1–4 Gy). The TLD reading procedure is destructive but OSLDs and RPLDs can be read repeatedly and the signal depletion per reading is 0.036% for OSLDs and 0.017% for RPLDs. The sensitivity correction factors for RPLDs and OSLDs were determined with the standard deviation in response of 1000 dosimeters of 2.2% for OSLD and 0.9% for RPLD. The combined standard uncertainties (k = 1) are 1.60% for TLDs, 1.46% for OSLDs and 1.51% for RPLDs. All three systems can be successfully used for auditing purposes if corrections for all described effects are applied. Highlights: All three dosimetry systems are appropriate for use in large-scale remote audits. Each audit methodology requires independent commissioning process. All tested systems were found to have intrinsic advantages and disadvantages.