Dose response of rat retinal microvessels to proton dose schedules used clinically: A pilot study

Purpose: This preclinical rat pilot study quantifies retinal microvessel, e ndothelial, and pericyte population changes produced by proton irradiation. Methods and Materials: The left eyes of rats were irradiated with single do ses of 8, 14, 20, and 28 Gy protons; right eyes, with two fractions, Animal s were euthanized, and eyes mere removed; elastase digests were prepared, a nd cell populations were counted in sample fields. Results were compared wi th unirradiated controls. Results: Progressive time- and dose-dependent endothelial cell loss occurre d following all schedules. Cell loss was significantly different from contr ol values (p < 0.001) following 28 Gy and following 20 Gy (p < 0.05) in a s ingle dose, Endothelial cell loss was the same for single- and split-dose s chedules. Progressive endothelial cell loss produced vessel collapse and ac ellular vessel strands, Endothelial cells were in the G(o) phase of the mit otic cycle. 28 Gy produced photoreceptor cell loss, Conclusion: The retinal digest is an elegant bioassay to quantify the micro vessel population response. Single- and split-dose schedules appear to yiel d similar outcomes, in terms of endothelial cell density, (C) 2000 Elsevier Science Inc.