No association between excessive wound complications and preoperative high-dose, hypofractionated, image-guided radiation therapy for spine metastasis
Authors: Keam Jennifer , Bilsky Mark H. , Laufer Ilya , Shi Weiji , Zhang Zhigang , Tam Moses , Zatcky Joan , Lovelock Dale M. , Yamada Yoshiya 
Published: February 2014

Object
Radiation therapy is known to impair wound healing. Higher dose per fraction is believed to increase this risk. This study sought to quantify rates of wound complication in patients receiving preoperative conventionally fractionated radiotherapy (XRT) or high-dose hypofractionated image-guided radiation therapy (IGRT) for spinal metastasis, and to identify predictors of wound complication.

Methods
The records of 165 consecutive patients who underwent spine surgery for metastasis at Memorial Sloan–Kettering Cancer Center between 1999 and 2010, with a history of prior radiation therapy, were reviewed. Patients with primary spine tumors, 2 courses of prior radiation therapy to the surgical site, total dose < 9 Gy, or radiation therapy adjacent to or partially overlapping the surgical site, were excluded. One hundred thirty patients received XRT (≤ 3 Gy/fraction) and 35 received IGRT (> 3 Gy/fraction). The total dose prescribed to the 100% isodose line to treat the planning target volume was 18–30 Gy in 1–5 fractions. Clinical factors evaluated included age, Karnofsky Performance Scale score, body mass index, presence of diabetes, smoking, ambulatory status, prior surgery at same spinal site, preoperative laboratory results (hemoglobin, lymphocyte count, and albumin), perioperative chemotherapy or steroids, estimated blood loss, extent of stabilization hardware, time between radiation therapy and surgery, number of vertebral bodies irradiated, total radiation dose, and dose per fraction of radiation therapy. Wound complication was defined as poor healing, dehiscence, or infection. Potential predictors of wound complication were assessed by univariate analyses using competing-risk methods to adjust for risk of death.

Results
For XRT patients, median dose was 30 Gy (range 11.5–70 Gy) with 72% of them receiving 3 Gy × 10 fractions. For IGRT patients, 66% received 18–24 Gy × 1 fraction and 23% received 6 Gy × 5 fractions. Groups differed only by the mean number of vertebral bodies treated (4.6 XRT and 1.8 IGRT, p < 0.0001). Wound complications occurred at a median of 0.95 months (range 0.4–3.9 months). A total of 22 wound events occurred in the XRT group and 2 in the IGRT group. The 6-month cumulative incidence of wound complications for XRT was 17% and for IGRT was 6%. There was no significant difference in wound complications between groups (IGRT vs XRT: hazard ratio 0.31, 95% CI 0.08–1.3; p = 0.11). Higher dose per fraction appeared to be associated with a lower risk of wound complication (hazard ratio 0.27, 95% CI 0.06–1.15; p = 0.08), which trended toward significance. Univariate analyses did not reveal any significant predictors of wound complications.

Conclusions
Patients who underwent XRT or IGRT did not have significantly different rates of postoperative wound complications. This finding may be explained by the treatment of fewer vertebral bodies in IGRT patients, or by the low overall number of total events. With a wound complication rate of 6%, preoperative IGRT, a highly conformal treatment, resulted in a very low rate of surgical wound complication.