Post-operative complications following dose adaptation of intra-operative electron beam radiation therapy in locally advanced or recurrent rectal cancer

Purpose:
The benefit of intra-operative radiotherapy (IORT) in the treatment of locally advanced rectal cancer (LARC) or locally recurrent rectal cancer (LRRC) lie in its ability to provide high-dose of radiation to limited at-risk volume, thereby eliminating microscopic disease and decreasing toxicity. A comparative study between high-dose-rate (HDR) brachytherapy, named intra-operative brachytherapy (IOBT), and intra-operative electron radiotherapy (IOERT) was performed showing favorable LRFS after IOBT, possibly due to a higher surface dose that is inherent in IOBT technique. The IOERT technique in Catharina Hospital Eindhoven was adapted to increase the surface dose, aiming to improve local control. Post-operative complications due to an increased radiation dose remain the matter of concern. This retrospective study was performed to compare complication rates before and after adapted IOERT dose.

Material and methods:
All patients undergoing surgery with IOERT for LARC or LRRC from September 2019 until July 2023, were considered. Patients selected until August 31, 2021 were included in control cohort (n = 108), and those chosen from September 1, 2021 onwards were included in intervention cohort (n = 92). Perioperative and (major) post-operative complications were classified retrospectively, during admission, at 30 days, and at 90 days.

Results:
In LARC patients, a decrease in post-operative complications was observed (p = 0.009). 19% of LARC patients experienced major post-operative surgical complications, i.e., Clavien-Dindo grade 3b-5, regardless of treatment group. No difference in major 90-day complications was noted (p = 0.142). In LRRC patients, the use of induction chemotherapy decreased from 78% to 29% (p < 0.001), which complicated comparison. However, no difference in major post-operative complications was observed at 30 days (p = 0.222) or 90 days (p = 0.977) after surgery.

Conclusions:
Increased surface dose of IOERT does not seem to lead to an increase in post-operative complications. Further research is needed to evaluate the efficacy of dose adaptation in IOERT to improve local oncological control rates. Routine evaluation of CTCAE scores in follow-up will help uncover possible long-term radiation-induced toxicity.