Complication and response assessment of high-dose-rate endorectal brachytherapy boost in neo-adjuvant chemoradiotherapy of locally advanced rectal cancer with long-term outcomes.

Purpose: To identify efficacy, complication, and pathologic response of high-dose-rate endorectal brachytherapy (HDR-BRT) boost in neo-adjuvant chemoradiotherapy (nCRT) of locally advanced rectal cancer.

Material and methods: Forty-four patients who met eligibility criteria were included in this non-randomized comparative study. Control group was recruited retrospectively. nCRT (50.40 Gy/28 fr. plus capecitabine 825 mg/m² twice daily) was administered to both groups before surgery. In the case group, HDR-BRT (8 Gy/2 fr.) was supplemented after chemoradiation. Surgery was done 6-8 weeks after completion of neo-adjuvant therapy. Pathologic complete response (pCR) was the study's primary endpoint.

Results: From 44 patients in the case and control groups, pCR was 11 (50%) and 8 (36.4%), respectively (p = 0.27). According to Ryan's grading system, tumor regression grade (TRG) TRG1, TRG2, and TRG3 were 16 (72.7%), 2 (9.1%), and 4 (18.2%) in the case, and 10 (45.5%), 7 (31.8%), and 5 (22.7%) in the control group (p = 0.118). T down-staging was found in 19 (86.4%) and 13 (59.1%) patients in the case and control groups, respectively. No grade > 2 toxicity was identified in both the groups. Organ preservation was achieved in 42.8% and 15.3% in the case and control arm (p = 0.192). In the case group, 8-year overall survival (OS) and disease-free survival (DFS) were 89% (95% CI: 73-100%) and 78% (95% CI: 58-98%), respectively. Our study did not reach median OS and median DFS.

Conclusions: Treatment schedule was well-tolerated, and neo-adjuvant HDR-BRT could achieve better T down-staging as a boost comparing with nCRT, without significant complication. However, the optimal dose and fractions in the context of HDR-BRT boost needs further studies.