Intra-operative Radiation Therapy for Colorectal or Anal Cancer at Risk for Margin-Positive Resection: Initial Results of a Single-Institution Registry.

Purpose: Pelvic recurrence of rectal or anal cancers is associated with considerable morbidity and mortality. We report our initial experience with an aggressive intra-operative radiotherapy (IORT) program.

Methods: Patients with locally advanced or recurrent rectal or anal cancers considered to have a high likelihood of R1 or R2 resection after multi-disciplinary review underwent surgical excision and IORT using a high-dose-rate afterloader (Ir-192) and HAM applicator. Endpoints included local or distant recurrence, and acute and late toxicity graded using the American College of Surgeons (ACS) NSQIP and the LENT-SOMA scale.

Results: Twenty-one patients, largely with prior history of both pelvic external beam radiotherapy (EBRT, median 50.4 Gy) and surgical resection, underwent excision with IORT (median dose 12.5 Gy, range 10-15). Median follow-up was 20 months. Twelve (57%) patients had failure at the IORT site. Freedom from failure (FFF) within the IORT field was associated with resection status (FFF at 1 year 75% for R0 vs 15% for R1/2, p = 0.0065) but not re-irradiation EBRT or IORT dose (p > 0.05). Twelve, 5, and 13 patients experienced local, regional, and distant failure, respectively; 3 (14%) patients were disease-free at last follow-up. The most frequent acute toxicity was sepsis/abscess (24%). One patient (5%) required a ureteral stent; no patients developed neuropathy attributable to IORT.

Conclusions: In patients treated with excision and IORT for locally recurrent cancer, R0 resection is a critical determinant of local control. For patients with R1/2 resection, poor disease-free outcomes warrant consideration of a different treatment strategy.