CORRELATION OF LOCAL FAILURE WITH MEASURES OF DOSE INSUFFICIENCY IN THE HIGH-DOSE SINGLE-FRACTION TREATMENT OF BONY METASTASES

Purpose: In the setting of high-dose single-fraction image-guided radiotherapy of spine metastases, the delivered dose is hypothesized to be a significant factor in local control. We investigated the dependence of local control on measures of dose insufficiency. Methods and Materials: The minimum doses received by the hottest 100%, 98%, and 95% (D-min, D-98, and D-95) of the gross target volume (GTV) were computed for 91 consecutively treated lesions observed in 79 patients. Prescribed doses of 18-24 Gy were delivered in a single fraction. The spinal cord and cauda equina were constrained to a maximum dose of 12-14 Gy and 16 Gy, respectively. A rank-sum test was used to assess the differences between radiographic local failure and local control. Results: With a median follow-up of 18 months, seven local failures have occurred. The distributions of GTV D-min, D-98, and D-95 for treatments resulting in local failure were found to be statistically different from the corresponding distributions of the patient group as a whole. Taking no account of histology,p values calculated for D-min, D-98, and D-95 were 0.004, 0.012, and 0.031, respectively. No correlations between local failure and target volume or between local failure and anatomic location were found. Conclusions: The results indicate that D-min, D-98, and D-95 may be important risk factors for local failure. No local failures in any histology were observed when D-min was >15 Gy, suggesting that this metric may be an important predictor of local control. (C) 2010 Elsevier Inc.