Skin graft survival after external beam irradiation

Difficulties with skin graft ulceration after radiation therapy for cancer have led many to question the suitability of this method of soft-tissue cov erage and its cost-effectiveness. The objective of this study was, therefor e, to assess skin-graft integrity subjected to postoperative external beam irradiation in a rat model. The model consisted of a rectangular full-thick ness skin graft raised and reapplied to its original bed on the dorsum of e ach rat. Five groups of adult male Sprague-Dawley rats (n = 8 per group) we re established. Group A was the control group and was not given postoperati ve irradiation. Groups B, C, D, and E received postoperative unfractionated cobalt(60) irradiation 4 weeks after gr grafting for a total dose of 15, 2 0, 25, or 30 Gv, respectively. Weekly skin-graft evaluation was performed f or the 4 weeks after irradiation (8 weeks after surgery) by measuring areas of graft loss using computerized planimetry. After the animals were killed, histologic samples were obtained from normal unirradiated skin and from both intact and ulcerated skin-graft sites. Gra ft loss after irradiation of 20 Cv was similar to that of the unirradiated controls. Occurring as early as 1 week after treatment, a two-fold increase in graft ulceration was observed with doses of greater than or equal to 25 Gy (P = 0.0007). Only partial healing of ulcerations was noted by thr four th week after treatment. Histologic changes associated with the irradiation of skin grafts using doses of 25 Gy or higher included hyaline degeneratio n, fibrinoid necrosis, telangiectasia, and edema. Granulation tissue predom inated as a mechanism of healing in areas of graft ulceration. The intensit y of inflammatory cell infiltrate did not correlate with radiation dose. Th e authors concluded that postoperative, unfractionated irradiation can indu ce skin-graft loss at doses of 25 cv or higher. Fractionated irradiation or longer intervals between grafting and irradiation may increase skin-graft tolerance: however, further studies al-e warranted.