High-dose-rate vs. low-dose-rate interstitial brachytherapy boost for anal canal cancers

The purpose of this study was to analyze and compare clinical outcomes of low-dose-rate (LDR) and high-dose-rate (HDR) interstitial brachytherapy boost (ISBT) after EBRT or radio chemotherapy for the treatment of anal canal cancers.

One hundred patients with anal canal cancers were treated at our institution by ISBT [LDR (n = 50); HDR (n = 50)]. Chronic toxicity rates, local control, disease-free survival, overall survival, and colostomy-free survival of the two different dose-rate brachytherapy modalities were analyzed and compared.

With a median followup of 42.2 months (95% CI, [34.5-48.8]), 9 (9% [4.8-16.2%]) local recurrences were observed, 4 (8% [3.2-18.8%]) in LDR vs. 5 (10% [4.4-21.4%]) in HDR group (odds ratio [OR] = 1.28 [0.32-5.07], p = 0.73). The 5-year rate of local control for the entire population was 90% [81-95%], 93% [79-98%] vs. 86% [69-94%] for LDR and HDR, respectively (p = 0.38). The 5-year disease-free survival rate for all patients was 82% [71-90%], 88% [73-95%] vs. 72% [44-88%] for LDR and HDR, respectively (p = 0.21). The 5-year overall survival rate for global population was 94% [84-98%], with no significant differences between LDR (97% [79-100%]) and HDR (93% [80-98%]) (p = 0.27). The 5-year colostomy-free survival rate was 92% [83-96%], respectively, 95% [83-99%] vs. 86% [69-94%] for LDR and HDR (p = 0.21). Significant differences were found in terms of chronic toxicity rates, with 28 (56% [42.3-68.8%]) patients concerned in low-dose-rate brachytherapy vs. 17 (34% [22.4-47.9%]) in high-dose-rate brachytherapy (OR = 0.40 [0.18-0.91], p = 0.03).

Local recurrence rates were comparable between both groups; HDR brachytherapy seem to have a better toxicity profile. Our data confirmed the finding that HDR can be used to safely administer ISBT without increasing chronic toxicity.