Intensification of local therapy with high-dose rate intraoperative radiation therapy (HDR-IORT) and extended resection for locally advanced and recurrent colorectal cancer.

Abstract

126 Background: This study reports our long-term experience with high dose rate intraoperative radiotherapy (HDR-IORT) in a single, quaternary institution. Methods: From 2004-2020, 138 consecutive patients with 141 total resections for locally advanced rectal cancer (LARC) (n=60, 43%) defined as T4Nx or T3N+ or locally recurrent rectal cancer (LRRC) (n=81, 57%) were retrospectively reviewed. The median age was 61 years (range 31-83) with 30 patients aged >70 years during surgery. Most patients had preoperative radiotherapy (RT) +/- concurrent chemotherapy (n=125). Thirty-two recurrent cancers received preoperative pelvic reirradiation to a median dose of 36 Gy (range 34.2 – 41.4). HDR-IORT was delivered using isotope iridium-192 in a remote afterloader, and a Freiburg applicator, after macroscopic resection of the tumour. A single 10 Gy fraction was delivered. Fifty-eight of 84 patients who underwent pelvic exenterations had >3 en bloc organs resected, and 96 patients underwent pelvic sidewall dissections. IORT sites included the primary tumour bed (33%), nodal regions (28%) and wider pelvic areas (70%). Resection margin status were R0 in 76 patients (54%) and R1 in 65 (46%). R1 resection was defined as positive (n=53) or close (n=12). R1 resection patients accounted for 61% of pelvic relapses. Results: With a median follow-up time of 4 years, 3-, 5-, and 7- year, overall survival (OS) rates were 75%, 48%, and 45%, respectively (84%,58%, 58% for LARC and 68%,39%, 35% for LRRC). Local progression-free survival (LPFS) of all patients were 88%, 85%, and 85%, respectively (97%, 93%, 93% for LARC and 80%, 80%, 80% for LRRC). On multivariable analysis, an R1 resection was associated with a trend toward poorer OS (p=0.05), while a trend towards worse LPFS (p=0.07) was noted for those without preoperative RT. The most common severe (grade ≥3) adverse events were postoperative abscess (n=25) and bowel obstruction (n=11). Overall, there were 49 (34%) grade 3-4 and no grade 5 adverse events. No intraoperative complications were attributed to IORT. The 30-day mortality rate was 0%. Conclusions: Favorable OS and LPFS can be achieved with intensive local therapy. As R1 resection may be associated with worse survival, optimisation of IORT, surgical resection, and systemic therapy are required. [Table: see text]