Single-fraction image-guided extracranial radiosurgery for recurrent and metastatic abdominal and pelvic cancers: short-term local control, metabolic response, and toxicity.

PURPOSE: Extracranial radiosurgery (ECRS) is a novel treatment for inoperable recurrent or metastatic abdominopelvic cancers. However, local control, metabolic response, and acute toxicity remain undefined. We therefore analyzed these endpoints in patients treated with single-fraction image-guided ECRS at Emory University.
METHODS: 20 patients with recurrent or metastatic inoperable abdominal or pelvic cancers (23 sites) were treated with single-fraction ECRS using a Varian linear accelerator between 08/2006 and 02/2008. Patients with pancreas, biliary and liver cancer were part of an IRB-approved ongoing dose-escalation trial. 14 patients had received prior abdominal or pelvic external beam radiation. In 13 patients pre-treatment PET/CT was used to delineate the target volume. Image-guidance was provided by implanted fiducial markers and on-board imaging in 13 patients, and with cone-beam CT in 1 patient. 8 Patients were treated with respiratory gating. The median single-fraction dose delivered was 18 Gy. Each patient was assessed at 1 week, 1 month, and 3 months after radiosurgery for toxicity, and at approximately 1 month and 3 months with PET/CT for metabolic tumor response. Partial response was defined as a reduction in size of > 10% on CT and a decrease in maximum SUV of > 15% on PET. Complete response was defined as complete resolution on CT, and a reduction of SUV to background levels on PET.
RESULTS: The median follow-up was 6.3 months (range 1.5-12.2 months). The overall response rate (the sum of complete responses and partial responses) by treated site was noted in 36% (1 month), 47% (3 months) and 48% (final). A complete response was achieved in 13% (3 sites). At last follow-up, local control (sum of response rate and stable disease) was 74%. The metabolic response rate by pet only(sum of partial and complete responders) was 85% on final analysis. 23% of pet avid sites achieved a complete response. Two pet avid treated sites (13%) did show evidence of progression at 3 months, but subsequent CT/FDG-PET scans showed a decrease in maximum SUV; no patients suffered progressive disease based on metabolic imaging at last follow-up. Grade 1-2 upper GI acute toxicity (nausea, vomiting, gastritis, and pain) was noted in 47% and 55% of patients at 1 week and 1 month, respectively. Correspondingly, acute lower GI toxicity (diarrhea, pain) was lower at 12% and 6%. Overall grade 1-2 GI toxicity was seen in 59% of patients at 1 week (pain and nausea being the most common) and 61% of patients at 1 month post stereotactic body radiotherapy (SBRT) (nausea being the most common).
CONCLUSIONS: Single-fraction image-guided ECRS for recurrent or metastatic abdominopelvic cancers is safe and effective in the short term. 3-month local control was very good , and was predicted by an early metabolic response as seen on PET/CT. Acute side effects were mild, with no patient experiencing grade 3 or greater toxicity. Dose escalation and long-term studies are warranted for this treatment approach.