Results of a remote audit program of reference and non-reference dosimetry of photon beams using alanine detectors

Abstract

Background and purpose: Remote beam output audits (BOAs) are important for verifying the calibration of the audited beam. However, BOAs (Level I audit) provide limited independent validation of the commissioned beam model in the treatment planning system (TPS). With Level II audits, the beam commissioning data is checked more thoroughly. This study presents the results of a remote audit program of reference and non-reference dosimetry, utilising alanine dosimetry. A particularity was to use the calculations of the TPS as reference values corrected by the daily output. The goal was to verify the beam commissioning data in the TPS, including the calibration. Materials and methods: The audit consisted of five irradiations with a 10 x 10 cm2 field and a small field test with field sizes up to 2 x 2 cm2. Watertight sealed alanine detectors, along with a 3D-printed holder featuring three slots at depths of 8 cm, 10 cm, and 20 cm, were used. The results of 224 beams audited were included in this study. Results: The difference between the measured and predicted doses was within +/- 5 % for all beams except one. No clear trend was observed in the results for uniform and FFF beams. The uncertainty in the alanine readout was 1 % (k =1). The results maintained their accuracy, while a slight improvement was observed in the small field test. Conclusions: All audit results were satisfactory. There is a slightly positive trend in the audit results over the years, suggesting that the accuracy of radiotherapy calculations is consistently maintained.