A prospective case series assessing the Imperial College London intraoperative radiotherapy protocol for advanced rectal cancer: an IDEAL phase 2a study.

AIM: Intraoperative radiotherapy (IORT) decreases local recurrence rates for advanced rectal cancer. Nevertheless, utilization of IORT is limited due to the associated logistical and financial challenges. The aim of this study is to describe the development and delivery of a novel IORT protocol for advanced rectal cancer that overcomes these difficulties in the context of the early phase of an IDEAL 2a study. The primary outcome measure was the ability to deliver IORT using this novel protocol with IORT-related toxicity as the secondary outcome measure.

METHOD: Consecutive patients with advanced rectal cancer expected to have involved (R1) resection margins were enrolled. After resection, 12 Gy low-energy photon IORT was delivered using the Axxent device with a custom-designed elliptical spherical balloon applicator.

RESULTS: Six patients with a median age of 47 years (range 33-88 years; five women) were enrolled between 2018 and 2019. The indication was advanced cancer in four patients and atypical invasive pelvic side wall lymph nodes in two. IORT was successfully delivered in all cases. No toxicity was encountered. Three advanced cancer patients had R1 resection and one had complete resection (R0); resection margin status could not be established for the two lymph node cases. Five patients were alive at 3.4 (2.9-4.1) year follow-up. None of the R1 cases recurred.

CONCLUSION: This is the first study to describe a novel IORT protocol using low-energy photon IORT for advanced rectal cancer. IORT could be delivered in all cases and no IORT-related toxicity was encountered. Available oncological outcome data are encouraging, but further studies will be necessary to determine the oncological effectiveness of this protocol.