Dosimetric Characterization and Workflow Optimization of the FLASH-SARRP for Reliable Preclinical Radiobiological Studies

Abstract

Objective: The reliable use of preclinical small-animal irradiators requires dosimetric characterization and quality assurance (QA) protocols. This study aimed to characterize the FLASH-SARRP, a dual-tube small-animal X-ray irradiator capable of ultra-high dose-rate (UHDR) delivery, as well as to establish and validate a practical QA workflow that improves dose reproducibility for preclinical FLASH experiments. Approach: A combined dosimetric approach using Gafchromic films for spatial dose assessment and a plastic scintillating fiber for real-time temporal monitoring, was used to evaluate beam characteristics. Custom 3D-printed spacers were designed to ensure reproducible experimental configurations. The temporal pulse structure of the two X-ray tubes and their synchronization during simultaneous irradiation were investigated using scintillating fiber measurements. Based on the findings of the two dosimeters, a QA workflow was implemented and validated, which uses a cross-calibration between the Gafchromic film and the scintillating fiber in the experimental setup, followed by pre-irradiation verification with the fiber to compensate for day-to-day output variations. Main results: Simultaneous irradiation of both X-ray tubes achieved dose-rates of approximately 80 Gy/s inside a homogeneous irradiation field suitable for small-animal studies. Temporal measurements revealed an average delay of 10 ms in between the two X-ray tubes, resulting in temporal dose-rate heterogeneity throughout the delivery of the dose. Additionally, a substantial inter-session variability of approximately 11% was found, whereas the intra-session variability was relatively low around ~4%. Implementation of the proposed QA workflow reduced the inter-session variability to around 5%, approaching the intrinsic intra-session variability of the machine. Significance: This work highlights the importance of temporal dosimetry for preclinical FLASH studies, as a measurable desynchronization between the two X-ray tubes was identified, generating temporal dose-rate heterogeneity that would not be detected by integrated dose measurements alone. The proposed QA framework improves reproducibility and provides a practical approach for reliable preclinical investigations.