MSOR03 Presentation Time: 8:10 AM

Purpose

Despite advances in surgical techniques and multimodality therapy for anal canal and rectal cancers, local recurrence and unresectable disease remain a significant challenge, often associated with poor quality of life. It is not clear how best to address this entity in the absence of large prospective randomized trials. The aim of this study was to retrospectively evaluate the outcomes and toxicities of pelvic low dose rate brachytherapy (LDR) combined with surgical resection in patients with unresectable and locally recurrent anorectal cancers.

Materials and Methods

Following IRB approval, patients with biopsy-proven anorectal cancers who underwent LDR during surgery for unresectable or locally recurrent anorectal cancers from 2004 to 2022 were included. Patients who had LDR for recurrent gynecological or genitourinary cancers were excluded. For all patients, the intent of surgery was complete resection of all visible disease. This was followed by LDR, either in the surgical bed for recurrent cancers or the site of microscopically positive margins for the unresectable patients. Following LDR mesh fixation with sutures, an omental flap was draped over the site of LDR to prevent seed migration and to minimize dose to organs at risk. Toxicity grading was done using the Common Terminology Criteria for Adverse Events (CTCAE) Version 5.

Results

Out of 29 eligible patients, 20 underwent Iodine-125 LDR, and 9 received Cesium-131 LDR with an average of 73.8 sources used per patient. The primary site was colorectal in 79.3% and anal canal in 20.7%. 27 (93.1%) of the patients had pelvic only disease at the time of LDR and surgery. 21 (72.4%) patients had at least 1 surgery prior to the implant prior to the implant, whereas 8 (27.6%) patients had no surgery prior to the implant. Brachytherapy was offered at recurrence in 23 patients (79.3%) and in 6 (20.7%) patients who were considered unresectable initially. In those with recurrences, 20 (87.0%) had LDR offered during their first recurrence and the rest were offered LDR at subsequent recurrences. Chemotherapy was offered at first recurrence in 21 (91.3%) patients. No Grade 4 or 5 toxicities were reported. The most common adverse event seen was neuralgia in 12 (41.4%) patients with 2 of those developing Grade 3 neuralgia. The rate of Grade 2 gastrointestinal fistula was 5 (17.2%) and Grade 2 urinary fistula was 3 (10.3%). All of the patients who developed fistulas were diverted at the time of surgery and LDR or before, and did not require additional invasive interventions. The 12 month and 24 month local progression free survival were 55.4% (95% CI: 34.9-71.8) and 41.7% (95% CI: 22.3 - 60.1), respectively. The 12 month and 24 month progression free survival were 38.4% (95% CI: 20.7-55.9) and 25.6% (95% CI: 10.9-43.3), respectively. The 12 month and 24 month overall survival rates were 88.7% (95% CI: 69.0-96.2) and 70.6% (95% CI: 47.7-84.9), respectively.

Conclusions

LDR in combination with resection of all macroscopic disease in unresectable or locally recurrent anorectal cancers is a viable treatment option. Toxicities are acceptable, with no Grade 4 or 5 adverse events in this cohort. Fistulas were managed expectantly as the patients who developed fistulas were already diverted. Furthermore, it is not clear if the fistulas developed as an adverse event of LDR or were due to local tumor progression. Progression free survival and overall survival at 12 and 24 months align with prior retrospective reports. Our study is subject to the limitations of being a retrospective study with a small sample size. However, the findings are encouraging and warrant further prospective studies to guide the management of these heterogenous and often challenging cases.