O-0014 - Intraoperative Radiotherapy Reduces Local Recurrence Rates in Patients with Locally Advanced Rectal Cancer with Microscopically Involved Circumferential Resection Margins

Abstract

Background: Local control is one of the main goals of the surgical treatment of rectal cancer. The most important predictive factor for local control is the circumferential resection margin (CRM). Unfortunately, CRM involvement still occur in 19-24% of the patients with locally advanced rectal cancer (LARC), despite using (chemo-) radiotherapy and total mesorectal excision (TME). In these patients, local recurrence rates may be reduced by administering intra-operative radiotherapy (IORT). One single dose of IORT is considered the biological equivalent of two to three times the dose given by conventional fractionation and this dose preceded by an external radiation dose should be sufficient to eradicate microscopic remnant. Furthermore, IORT may also be beneficial in patients with radical resections with a clear but narrow CRM (<2mm), because these patients also have a higher risk of local recurrences. This study evaluated the effect of IORT in patients with LARC after TME with a microscopic involved CRM or a clear but narrow CRM. Methods: Between 1996 and 2012, all surgically treated patients with LARC and a CRM less than 2 mm after (chemo-)radiotherapy followed by TME were analyzed. These patients were divided into a group with radical resections with a clear but narrow CRM (<2mm) and a group with a microscopic involved CRM. In these groups, the outcome of the patients who were treated with IORT was compared with the outcome of patients who were treated without IORT. Results: Ninety-five of the 409 surgically treated patients with LARC had a CRM less than 2mm after neoadjuvant (chemo-)radiotherapy based on final pathology report. Forty-three patients had a radical resection with a clear but narrow CRM and 48 patients had a microscopic involved CRM. Four patients were excluded from further analysis due to a macroscopic non radical resection. Of the patients with radical resections with a clear but narrow CRM, 21 patients were treated with IORT and 22 patients were treated without IORT. The baseline characteristics of the patients treated with and without IORT were similar. There was no difference in the cumulative 5-years local recurrence-free survival (70 vs. 79%, p = 0.63). Of the patients with a microscopic involved CRM, 31 patients were treated with IORT and 17 patients were treated without IORT. Baseline characteristic of the patients treated with and without IORT were similar, except that patients treated without IORT had more stage IV disease (52 vs. 13%, p = 0.01). In this group, there was a significant difference in the cumulative 5-years local recurrence-free survival in favor of the 31 patients treated with IORT compared with the 17 patients who were not treated with IORT (84 vs. 41% p = 0.01). Multivariable analysis confirmed that IORT was independently associated with a decreased local recurrence rate in these patients. Conclusion: IORT reduces local recurrence rates in patients with LARC with a microscopic involved CRM.