Assessment of FLASH Radiation Doses Using Polycrystalline Alanine Powder as a Passive Dosimeter

FLASH radiation therapy is a promising modality that delivers radiation at ultra-high dose rates, potentially minimizing normal tissue toxicity while maintaining tumor control. However, conventional dosimetry tools often fail at ultra-high dose rates, necessitating alternative solutions. Alanine dosimetry, a passive technique known for its dose-rate independence and tissue equivalence, presents a compelling option. While other studies have used alanine pellets, this study investigates the applicability of alanine powder dosimeters in FLASH radiation therapy. Thirteen dosimeters were irradiated with doses from 10 to 100 Gy using a 137 Cs source. Six samples were used to construct dose-response calibration curves, while the remaining seven were used for validation. Peak-to-peak amplitudes of the electron paramagnetic resonance signal were normalized using internal standards and sample density. Dose estimates based on density-normalized calibration were within ±4.2% of expected values, demonstrating strong linearity (R 2 > 0.99) and clinical viability. While post-processing time remains a limiting factor, this work affirms the potential of alanine powder as a reliable tool for FLASH dosimetry, especially for high-dose, dose-rate-independent measurements.