3438 - Long-Term Outcomes of Intraoperative Electron Radiotherapy (IOERT) in Locally Advanced and Recurrent Colorectal Cancer: A Single-Institution Experience

02:30pm - 03:45pm PT

Hall F

Screen: 3

POSTER

Presenter(s)

Abdullah Alswilem, MBBS - King Saud University Medical City, Riyadh, Riyadh

K. K. Hassan^1,2, A. M. Alswilem¹, S. Aljabab¹, Y. M. Alayed¹, and A. A. Alsuhaibani¹; ¹Oncology Center, Medical City, King Saud University, Riyadh, Saudi Arabia, Riyadh, Saudi Arabia, ²Kasr Al-Ainy Center of Clinical Oncology (NEMROCK), Cairo University, Cairo, Egypt, Cairo, Egypt

Purpose/Objective(s):

Intraoperative electron radiotherapy (IOERT) is a dose-escalation technique used to enhance local control (LC) in locally advanced (LA) and recurrent colorectal cancer (CRC), particularly in cases with suspected close or positive margins. Despite potential benefits, IOERT remains controversial due to mixed oncological outcomes and toxicity concerns. This study evaluates the long-term efficacy and safety of IOERT based on our institutional experience.

Materials/Methods:

Between 2017 and 2022, 39 patients with LA or recurrent CRC received IOERT as part of a curative multimodal approach. All had high-risk features, including T4b tumors (83%) with a median tumor diameter of 8.2 cm, elevated carcinoembryonic antigen (CEA >5 ng/mL) (46%), mucinous histology (33%), and limited metastases (28%). IOERT was given to the operative bed, commonly at the posterior or lateral pelvic wall; doses ranged from 10 to 15 Gray prescribed to the 90% isodose line, usually in a single-field application. The median cone size and treatment depth were 6 & 3 cm, respectively. A beveled angle between 15 to 30 degree was needed in 75% of cases. Systemic treatment and EBRT were commenced preceding or following IOERT as recommended by multidisciplinary team.

The primary endpoint was local control (LC). Secondary endpoints included time to distant metastases (TTDM), overall survival (OS), and treatment-related toxicity. Kaplan-Meier and Cox proportional hazards analyses were used for survival assessment.

Results:

The median patient age was 53 years. Pelvic exenteration and cytoreductive surgery were performed in 59% of cases. Although no gross residual disease was observed, 28% had positive resection margins.

Postoperative complications occurred in 74%, including urological injuries or stenosis (38%), wound-related complication (28%), and postoperative mortality (9%). No IOERT-related neuropathic symptoms were reported.

At a median follow-up of 72 months, the median time to local recurrence (LR) was not reached. The 2-year and 5-year LR rates were 27.9% and 35.6%, respectively. Local control was significantly better in non-recurrent than recurrent cases (5-year LC: 82% vs. 43%, P = 0.02). Positive margins did not significantly increase LR risk (P = 0.8), and mucinous histology showed a trend toward higher LR risk (P = 0.5).

Median TTDM was 33 months, favoring LA over recurrent cases (not reached vs. 33 months, P = 0.15). Median OS was 66 months, with 5-year OS rates of 75% (LA) and 58% (recurrent cases) (P = 0.1). High-grade tumors were associated with significantly worse OS (P = 0.004).

Conclusion:

These findings suggest IOERT improves LC in non-recurrent colorectal cancer and may mitigate the impact of positive margins. However, its role in recurrent disease remains uncertain. Further randomized trials are needed to compare IOERT-based and non-IOERT regimens to better define their oncological benefits and toxicity.