Outcomes of Squamous Cell Carcinoma Anal Canal treated with IMRT-VMAT-based Concurrent Chemoradiation: a Single Institutional Experience

Introduction: Chemoradiation is the standard of care in locally advanced carcinoma of the anal canal. However, the irregular surface and elective inguinal treatment poses a challenge for radiation planning and treatment with associated significant toxicity. In this retrospective study, we analysed the outcome of patients treated with intensity-modulated radiation therapy (IMRT) at our centre from 2012 to 2019.

Methods and materials: Records of patients treated with IMRT at our centre from 2012 to 2019 were reviewed. Patients with non-squamous histology and previous irradiation were excluded. Thus, 25 patients were found suitable for the study.

Results: Twenty-five patients with squamous cell carcinoma of the anal canal were treated at our centre from 2012 to 2019 using IMRT based chemoradiation. RTOG guidelines were followed for contouring and Varian Eclipse version 13(Palo Alto, California) was used for planning. Clinical response could be assessed in 20 patients and dosimetric data of all patients was available for review. The target volumes coverage goals as per ICRU 83 were achieved in all patients. The organ at risk constraints for bladder and femoral heads as per LATE-QUANTEC were achieved in most patients; however, the constraints for the rectum, testis and bowel bag were not achieved in the majority of the patients. The median duration of treatment break was 7 days. Mitomycin C and 5-FU or capecitabine were given concurrently with radiation. Eighteen patients (72%) received 2 cycles of chemotherapy, three (12%) received 1 cycle of chemotherapy while 4(16%) patients did not receive any chemotherapy. Median follow-up was 7.5 months. At median follow-up, 15(75%) patients were disease-free and asymptomatic, 2(10%) had residual disease and 3(15%) had progressive disease. Toxicity was assessed using CTCAE Version 5.0. Grade III skin toxicity was reported in 9(36%) of the patients and Grade III gastrointestinal toxicity was reported in 1 (4%) of the patients, no other grades III-IV toxicity was reported. Overall, the disease control was comparable to previous 3D-CRT studies but with much less toxicity.

Conclusion: IMRT-based chemoradiation should be the standard of care in locally advanced carcinoma of the anal canal.