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.