A Pre-Clinical Study of in vivo Irai and Biological Response during Flash and Conventional Electron Irradiation
Abstract
Purpose
Ionizing radiation acoustic imaging (iRAI) is a noninvasive technique for monitoring radiation delivery. Although iRAI acquisition during irradiation has been demonstrated, its use to quantify spatial dose variations alongside biological measurements under FLASH irradiation remains limited. This study evaluates the feasibility of using in vivo iRAI to characterize dose variations at the fall-off region of Percent Depth Dose (PDD) profiles under ultra-high dose rate (UHDR) and conventional electron irradiation and correspond these measurements to biological response in the abdomen.
Methods
Experiments were performed using a Mobetron electron accelerator operating at 9 MeV in conventional and UHDR (61.4 Gy/s) modes. A total dose of 14.32 Gy was delivered to the abdominal region of C57BL/6 mice using a 3 cm cutout. In vivo iRAI signals were acquired on a per-pulse basis using a 1D linear ultrasound array (Philips P4-1). Twenty-four mice were studied across FLASH and conventional cohorts with control and irradiated groups. A 2 cm bolus positioned the irradiation and iRAI measurement region between depths of 2.0 and 3.5 cm (95–45% dose), subdivided for PDD comparison. Animals were weighed at 24 hours, 3.5 days, and 30 days post-irradiation. Liver tissue was stained with Masson’s trichrome and analyzed using QuPath to assess radiation-induced fibrosis.
Results
FLASH mice exhibited reduced weight loss compared with conventionally irradiated mice, which showed significant early weight loss and a 79% reduction in long-term weight gain. At Day 30, liver fibrosis in FLASH mice was reduced by 91.5% relative to conventional mice. iRAI signal amplitude correlated strongly with depth-dependent PDD values (R² = 0.95 for FLASH; R² = 0.82 for conventional).
Conclusion
In vivo iRAI can characterize dose variations at the distal fall-off region under FLASH and conventional electron irradiation. When analyzed alongside biological endpoints, iRAI improves spatial localization of radiation delivery relevant to FLASH studies.