Investigation of alanine dosimeter for output measurement in radiotherapy: Results from multicenter in Thailand

Background: Alanine dosimeters are generally used in high-dose industrial applications (kGy). Later, research into employing alanine as a dosimeter in radiotherapy (1-20 Gy) has increased, since alanine may be an alternative transfer dosimeter for quality control, postal audit, and intercomparison between laboratories. However, several factors such as the dosimeter’s characteristic should be investigated while utilizing alanine in radiotherapy. In addition, the optimal electron paramagnetic resonance (EPR) reader should be configured to match the absorbed dose range. Objectives: This study aims to optimize the EPR setting parameters, study the characteristics of alanine dosimeters, and estimate the uncertainty of the 6MV-FFF linear accelerator in a dose ranging from 1 to 20 Gy. The output measurements from different facilities were also investigated. Materials and methods: The alanine dosimeters were irradiated with a 6MV-FFF beam using linear accelerator, Varian TrueBeam (Varian Medical Systems, Inc, CA, USA), 100 cm SSD, with a field size of 10x10 cm2 at 1 to 30 Gy. The EPR operation parameter has been optimized for these dose ranges. The characteristics of alanine dosimeters were then investigated, along with the estimation of uncertainty in using alanine. Finally, the alanine dosimeter proficiency was validated using 9 distinct linear accelerator machines. Results: The EPR parameters were found to be optimized at 1.589 mW of MP, 7.018 G of MA, and 40.96 ms of TC. The expanded uncertainty (k=2) was reported at 2.68% in the 1-20 Gy dose range. The alanine dosimeters’ characteristics were found to have good uniformity and reproducibility, low fading, and angle-and dose-independence. Although the investigation was performed in 9 different linear accelerator machines, the difference of delivered dose output was measured and reported with difference percentages within ±1%. Conclusion: This study reports the feasibility of using alanine dosimeters in radiotherapy. The important EPR parameter setting, and alanine dosimetry characteristics were investigated, whose results suggest that alanine can be used at a dose range of 1-30 Gy. This especially benefits the SRS treatment which uses a high dose per fraction, and this dosimeter can be an alternative transfer dosimeter. Nonetheless, various factors should be explored using an appropriate phantom prior to clinical application.