Retrospective Cohort of Patients Treated for Paraaortic and Paracaval Recurrence With Intraoperative Radiation Therapy

Abstract

Intraoperative electron radiation therapy (IOERT) may improve local control when combined with resection +/- external beam RT when there is concern regarding surgical margins (R1 or R2 disease). IOERT allows for delivery of additional radiation while minimizing dose to normal tissue as they can be physically removed from the RT field. While there is a strong body of literature on the use of IOERT in the pelvis, much less is known for treatment of paraaortic and paracaval tumors, where R0 surgical resection is difficult because of vascular or soft tissue involvement. We examined outcomes after surgery and IOERT for treatment of paraaortic and paracaval recurrences.We conducted a retrospective analysis of patients treated with IOERT to the paraaortic or paracaval region for nodal cancer recurrence between 2008 and 2020 at a single academic institution. Patients selected for IOERT in a multidisciplinary setting had isolated paracaval or paraaortic recurrence, and were deemed good candidates to undergo aggressive surgery with IOERT with curative intent. Overall survival (OS) and progression free survival (PFS) were calculated using Kaplan-Meier statistics with R statistical computing software.Twenty-six patients received IOERT to the paraaortic or paracaval region. Median follow up was 6.5 months (range 0-96). Primary cancer types included 19 colorectal, 2 appendiceal, 2 endometrial, 2 cervical, and 1 ovarian. Twelve patients (46%) had pre-operative EBRT to the paraaortic/paracaval area and 7 additional patients had EBRT to another site prior to IOERT (73% total prior RT). Two patients had multi-site IOERT. IOERT was delivered with 6-12 MeV electrons with 10-20 Gy per treatment (Table 1). One patient was treated to 2 sites and another to 3 sites. Of the 15 patients with known post-IOERT recurrences, 5 had isolated in-field local recurrences (LR), 7 had distant recurrences, and 3 had both local and distant recurrences. Two of the eight LR were in patients treated to multiple sites with IOERT with the LR in the pelvis (not included in paraaortic recurrence). Local control of paraaortic region at 1 year was improved when surgery had negative margins (83%) versus close margins (25%) or positive margins (0%) (Chi-squared P = 0.01). Crude local control in the paraaortic region with IOERT was 77%; it was 93% with negative margins and 58% with close or positive margins. The median OS of the entire cohort was 9 months, with 1 year OS of 64.6% (std error 11.0%), median PFS 4 months, and 1-year PFS of 32.6% (std error 11.6%). Of the 17 patients with colorectal cancer, 1 year OS was 70.2% (std error 12.8%) and 1-year PFS was 17.6% (std error 11.1%).IOERT to the paraaortic or paracaval region for cancer recurrence may contribute to local control for patients at high risk of local recurrence after surgery alone, although survival outcomes remain poor due to distant failures.