KEY POINTS
- The study included approximately 61 C57BL/6J mice assigned to untreated control, FLASH or conventional whole-brain irradiation cohorts, with individual experimental groups containing only two to six animals.
- Single fractions of 10, 15 or 20 Gy were delivered using 9 MeV electrons. FLASH used 1 Gy per pulse at an average dose rate of 240 Gy/s, compared with 0.1 Gy/s for conventional irradiation.
- Corneas were analysed four and 40 days after treatment using second-harmonic-generation microscopy. Outcomes included corneal thickness, forward-to-backward signal ratios and Fourier-based measures of collagen organization.
- Control corneal thickness was 36.5 ± 0.6 μm. Conventional irradiation increased thickness by 4.4%, 7.7% and 9.3% at day four and 9.9%, 10.7% and 21.6% at day 40 after 10, 15 and 20 Gy, respectively.
- FLASH produced smaller thickness increases at 10 and 15 Gy: −0.9% and 1.0% acutely and 5.8% and 3.8% chronically. The difference from conventional irradiation was significant at 15 Gy at day four (p = 0.0006) and day 40 (p = 0.0047).
- At 20 Gy, FLASH provided little protection against corneal thickening: increases were 8.5% versus 9.3% acutely and 18.1% versus 21.6% chronically with FLASH and conventional irradiation.
- Conventional irradiation produced lower forward-to-backward ratios and greater disruption of collagen lamellae. FLASH measurements remained closer to controls, although these structural analyses pooled all three dose levels and did not establish a dose-specific effect.
CLINICAL TAKEAWAY
The findings extend the experimental FLASH normal-tissue effect to corneal extracellular-matrix injury and suggest that protection may have a dose threshold. Translation remains remote: this was a single-fraction mouse experiment with very small groups, no visual-function assessment, no fractionated whole-brain regimen and no tumour model demonstrating preserved efficacy.