ESTRO 2025 - Abstract Book

S3926

Radiobiology - Normal tissue radiobiology

ESTRO 2025

Material/Methods: Twelve healthy male new zealand white rabbits received a single 3000 cGy irradiation dose in bilateral eyeballs (Figure 1a). Intravitreal melatonin (100 mcg/kg = 300mcg/0.05 mL) was administered to the left eyes of six rabbits, and bevacizumab (1.25 mg/0.05 mL) to the left eyes of the remaining six, with sham injections given to the right eyes as controls (Figure 1b). Six weeks after irradiation, bilateral enucleation was performed for histopathological evaluation.

Results: Electron microscopy of retinal tissue revealed distinct morphological alterations across the groups. In the sham group, capillaries exhibited characteristic endothelial thinning, basal lamina thickening, and perivascular collagen deposition, accompanied by intracytoplasmic edema within the pericytes. Axonal myelin demonstrated swelling and lamellation, with notable axonal thinning, nuclear clumping, cytoplasmic vacuolization in ganglion cells, and edema in the outer retinal segments. Conversely, in the melatonin group, capillary pericytes and endothelial cells appeared preserved, with no evidence of perivascular collagen deposition. Axonal structure and myelin thickness remained largely normal, and ganglion cells were largely intact. In the bevacizumab group, pericyte numbers and endothelial integrity were maintained, although perivascular collagenization persisted. While axons were generally preserved, localized areas exhibited edema and myelin sheath separation. Figure 2 presents a detailed analysis of the grades of retinal myelinated axonal damage observed across the experimental groups. In the sham group, 27 of 29 axons (93%) exhibited grade 1 or higher damage. In contrast, in the melatonin group, 23 of 29 axons (79%) were classified