The effects of radiation on neovascularization in a rat model

It is thought that radiation treatment inhibits neovascularization of recipient and/or graft tissues, and this may account in part for abnormalities in wound healing associated with radiation therapy. We have examined this hypothesis using a model that measures the neovascularization of an implanted foreign material. Expanded polytetrafluoroethylene (PTFE) sheets were implanted adjacent to both superficial epigastric vascular pedicles of 63 rats distributed into 7 groups (n = 7) that differed with respect to dose and timing of irradiation. Zero to 10 daily fractions of electron-beam radiation (300 cGy each) were delivered to the implant in the right groin, while the implant in the left groin served as a nonirradiated internal control. Unirradiated animals showed equal neovascularization of both implants. Rats that were irradiated twice (single fractions at 0 and 24 hours after implantation) did not show a significant decrease in the neovascularization of the irradiated implant compared with the contralateral control implant. In contrast, the implants that were irradiated three times (single fractions at 0, 24, and 48 hours after implantation) demonstrated significantly diminished ( > 25 percent, p < 0.05) neovascularization beyond day 7, whereas implants irradiated only at 48 hours after implantation did not. Interestingly, neovascularization of the implants irradiated with 10 fractions (3000 cGy) was not significantly decreased compared with irradiation with three fractions (900 cGy). Irradiation delivered before implantation (900 cGy) inhibited neovascularization significantly less than the same dose administered after implantation. The results of this study suggest that a subclinical cumulative dose of 900 cGy is the threshold for impaired tissue revascularization provided that treatment is delivered immediately after implantation over a 48-hour interval.