Efficacy and Safety of Low-Dose-Rate Endorectal Brachytherapy as a Boost to Neoadjuvant Chemoradiation in the Treatment of Locally Advanced Distal Rectal Cancer: A Phase-II Clinical Trial.

Purpose: Despite advances in rectal cancer treatment over the last decade, local control and risk of late side effects due to external beam radiation therapy (EBRT) remain as concerns. The present study aimed to investigate the efficacy and the safety of low-dose-rate endorectal brachytherapy (LDRBT) as a boost to neoadjuvant chemoradiation for use in treating locally advanced distal rectal adenocarcinomas.

Methods: This phase-II clinical trial included 34 patients (as the study arm) with newly diagnosed, locally advanced (clinical T3-T4 and/or N1/N2, M0) lower rectal cancer. For comparative analysis, 102 matched patients (as the historical control arm) with rectal cancer were also selected. All the patients were treated with LDRBT (15 Gy in 3 fractions) and concurrent chemoradiation (45-50.4 Gy). Concurrent chemotherapy consisted of oxaliplatin 130 mg/m(2) intravenously on day 1 plus oral capecitabine 825 mg/m(2) twice daily during LDRBT and EBRT.

Results: The study results revealed a significant differences between the study arm and the control arm in terms in the pathologic tumor size (2.1 cm vs. 3.6 cm, P = 0.001), the pathologic tumor stage (35% T3-4 vs. 65% T3-4, P = 0.003), and the pathologic complete response (29.4% vs. 11.7%, P < 0.028). Moreover, a significantly higher dose of EBRT (P = 0.041) was found in the control arm, and a longer time to surgery was observed in the study arm (P < 0.001). The higher rate of treatment-related toxicities, such as mild proctitis and anemia, in the study arm was tolerable and easily manageable.

Conclusion: A boost of LDRBT can optimize the pathologic complete response, with acceptable toxicities, in patients with distal rectal cancer.