Author: Gueorgui Gueorguiev, Katia Sergieva, Filip Simeonov, Tsvetelina Todorova, Bozhidar Vladimirov 👨🔬
Affiliation: National Centre of Radiobiology and Radiation Protection, Queen Giovanna University Hospital 🌍
Purpose: Dosimetry audit is an essential tool enhancing confidence in the accuracy of treatment delivery and in prevention of radiation treatment incidents. Current work depicts how novel nationwide remote dosimetry audit (RDA) system in radiotherapy, utilizing radiophotoluminescent dosimeters (RPLD), was commissioned and validated in Bulgaria.
Methods: Two hundred and seventy dosimeters were positioned in custom made PMMA phantom and irradiated with Co-60, then read and analyzed. An integral aspect of the RDA methodology using RPLD was the determination of factors applied to the RPLD reading in order to calculate the absorbed dose. Those factors corrected for dosimeter sensitivity, non-linearity dose response, energy, signal fading, and dosimeter holder. Applying the correction factors and Gy/count calibration coefficient to the RPLD counts gave the absorbed dose. Subsequently, the RDA methodology was successfully validated by dose comparison with ion chamber measurements and by participation in IAEA blind test. This validation was followed by a pilot RDA study in three Bulgarian radiotherapy centers using different linac clinical energies.
Results: After establishment of the RDA methodology, it was found that the combined type A and B uncertainty was 3% at k=1. Subsequently, the methodology was validated by RPLD dose comparison with ion chamber measurements on a single linac with 6MV, 10MV, 6FFF and 10FFF. The highest deviation between RPLD and ion chamber measured dose was observed with 10FFF and was found to be -1.1%. This difference was 0.2% for 6MV, 0.5% for 10MV and -0.9% for 6FFF. The pilot study results showed difference between dosimeter irradiated and dosimeter measured dose ranging from -1.48% to 2.04%.
Conclusion: The results showed that the proposed methodology for RPLD calibration is viable for implementing novel remote dosimetry audits in Bulgarian radiotherapy centers.