Intraoperative electron radiotherapy (IOERT) in colorectal cancer: Updated systematic review of techniques, oncological outcomes and complications

Background: Intra-operative electron radiotherapy (IOERT) directly delivers a large fraction of radiation to at-risk margins during surgery. However, the precise benefit of IOERT in patients with locally advanced and locally recurrent colorectal cancer (LACC/LRCC) is unclear. This study aimed to provide an updated summary of the current evidence available regarding IOERT as part of multi-modality treatment of LACC and LRCC. Method: This systematic review update was prospectively registered on PROSPERO (CRD42023438184). An electronic literature search was carried out using Ovid (MEDLINE), EMBASE, Web of Science, and the Cochrane Library databases for studies from July 2011 to April 2024. The inclusion criteria were adult patients who received IOERT as part of multi-modal treatment for LACC or LRCC. The primary outcome was overall survival (OS), disease free survival (DFS) and local control (LC) at 5 years. Secondary outcomes included post-operative complications. Results: 16 new studies were identified since the previous analysis, and included (study population 1912 patients) of which two were prospective. High heterogeneity prevented meta-analysis of outcomes except for 5-year OS which suggested a non-significant benefit favouring IOERT. Significant methodological concerns were identified making interpretations challenging, however patients with LACC or LRCC with an R1 resection margin showed a favourable 5-year OS (40 % and 18 % respectively) when compared to current evidence. Conclusion: Although limited by a lack of appropriately conducted randomised evidence, IOERT-containing multi-modality treatment may improve oncological outcomes in LACC and LRCC patients with R1 resections.