Optimizationand Performance Assessment of a Low-Dose Alanine Electron Paramagnetic Resonance Dosimetry Procedure for Potential Application in Electron Beam FLASH Radiotherapy

Alanine Electron Paramagnetic Resonance (EPR) is an established reference and transfer dosimetry method in high-dose applications, valued for its high accuracy and long-term stability. However, it exhibits increased uncertainties for doses below 10 Gy, where the Signal-to-Noise Ratio (SNR) is reduced. This work presents the optimization and performance assessment of an alanine EPR measurement procedure for quantitative dose measurements below 10 Gy using a traceable 60Co reference irradiation source under conventional irradiation conditions. The effects of pellet position within the resonant cavity, number of pellets measured simultaneously, microwave power, modulation amplitude, and acquisition time were systematically investigated. The optimized procedure used a two-pellet configuration positioned at a cavity holder control screw length of 9 mm, a microwave power of 1.8 mW, and a modulation amplitude of 0.4 mT. The total spectral acquisition time was 20 min, made of 120 s sweep time and 10 accumulated scans for a magnetic field sweep width of 2 mT. Although consistent spectral resolution was achieved at 1 Gy, exploratory measurements from 1 to 10 Gy showed an uncertainty of 15.88% (k = 2), providing a coverage probability of approximately 95%. This did not support the establishment of a reliable quantitative calibration. As such, a practical calibration range of 4–10 Gy was then established using dose points at 4, 5, 6, 8, and 10 Gy and verified at 4.5, 7.0, and 9.0 Gy, with absolute percentage dose differences ranging from 0.00 to 4.44%. A repeatability test assessed at 7 Gy gave a relative standard deviation of 0.77%, indicating consistent EPR response under repeated measurements for the optimized procedure. The uncertainty of measurements in the range of 4–10 Gy was determined to be 5.40%, with a coverage factor of k = 2. These findings demonstrate the performance of the optimized low-dose alanine EPR procedure over a practical range of 4–10 Gy. This supports further investigation of alanine EPR as a potential independent dosimetry method for electron beam FLASH RT studies.