Efficacy and tolerance of high-dose-rate brachytherapy boost after external radiotherapy in the treatment of squamous cell carcinoma of the anal canal.

Purpose: The aim of this study was to evaluate the efficacy and toxicity of high-dose-rate brachytherapy (HDR-BT) boost in anal squamous cell carcinoma (ASCC). Material and methods: This was a monocentric retrospective study involving patients treated by external irradiation (+/- chemotherapy), with HDR-BT boost, for a localized ASCC. Clinical evaluation was performed every six months. Oncological results were analyzed with: local relapse-free survival (LRFS), colostomy-free survival (CFS), metastatic-free survival (MFS), disease-free survival (DFS), and overall survival (OS). Acute and late toxicities were collected (CTCV4.0) and LENT/SOMA score was performed. Results: From May 2005 to January 2018, 46 patients (pts) were analyzed. The median follow-up was 61 months (10-145 months), the median age was 65 years (34-84 years), with a sex ratio M/F = 0.24. The TNM classification was as follows: T1 - 13 pts (21.7%), T2 - 34 pts (73.9%), T3 - 2 pts (4.3%), N+ - 6 pts (13.1%). External beam radiotherapy (EBRT) delivered a median dose of 45 Gy (36-50.4 Gy) in 25 fractions, and HDR-BT 12 Gy (10-18 Gy) in 3 fractions. The median overall treatment time (OTT) was 58 days (41-101 days), with a median EBRT/brachytherapy interval of 17 days (4-60 days). Oncological findings showed 5-year rates of LRFS 81.2%, MFS 88.7%, DFS 70%, and OS 90%. All abdominoperineal amputations were performed in case of local relapse (4 pts, 8.7%), leading to a 5-year CFS of 79.5%. Acute urinary toxicities were frequent (G1 41.3%, G2 4.3%). The acute digestive toxicities were: G1 71.7%, G2 6.5%, and G3 2.2%. The late urinary toxicities were: G1 4.3%, G2 2.2%, and G3 2.2%. Late digestive toxicities were: G1 56.5%, G2 8.7%, G3 2.2%, and G4 2.2%. Conclusions: In ASCC management, HDR-BT boost appears to be a treatment with a long-term acceptable toxicity profile, shorter than EBRT boost, with a reduction of side effects.