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Abstract
Aim. To evaluate the complete clinical response (cCR) rate following neoadjuvant external beam radiotherapy (EBRT) with endorectal high-dose-rate brachytherapy (ERHDRBT) boost for residual tumor in patients with cT2-3N0-2 low rectal adenocarcinoma.
Materials and Methods. A preliminary analysis included 48 patients with low rectal adenocarcinoma (cT2-3N0-2). Neoadjuvant therapy consisted of EBRT (23-25 fractions of 2 Gy or 5 fractions of 5 Gy) followed by an ERHDRBT boost (3 fractions of 7 Gy) to endoscopically marked residual tumor. Clinical complete response was assessed using standardized criteria: digital rectal examination (absence of palpable mass), endoscopic evaluation (white scar tissue), and magnetic resonance imaging (MRI) findings consistent with complete response.
Results. At 8-12 weeks post-treatment, cCR was achieved in 25/48 patients (52 %). Near-complete response was observed in 6 additional cases. Among 17 surgically managed patients without cCR, pathologic complete response (pCR) was confirmed in 7 cases (41.2 %). The overall complete response rate (cCR + pCR) was 66.6 % (32/48 patients). Response rates varied by stage: cT2N0-1 patients achieved 80 % complete response (16/20), while cT3N0-2 patients showed 60.7 % complete response (17/28). Late grade I-II rectal complications occurred in 29 % of non-operated patients, with no grade III or higher toxicities observed.
Conclusion. ERHDRBT boost to residual tumor following neoadjuvant EBRT yields high complete response rates (60.7-80 %) in low rectal cancer. The substantial pCR rate among surgically managed patients without cCR suggests the need for refined cCR criteria and/or optimized response assessment timing.
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