Image-guided high-dose-rate brachytherapy after short-course external beam radiotherapy for elderly/frail rectal cancer patients.

PURPOSE: For elderly and frail patients with rectal cancer, unfit for radical surgery or extensive chemoradiation schedules, radiotherapy dose escalation by use of high-dose-rate brachytherapy (HDR-BT) may be an alternative organ-preserving approach. METHODS: 15 elderly/frail patients (median age, 83 years; ECOG 1‑2: 80%) with histologically confirmed rectal adenocarcinoma (T1-3, N0-1, M0; UICC stage I-IIIB) were treated with definitive radiotherapy consisting of external beam radiation therapy (EBRT) of 30-39 Gy in 10-13 fractions, followed by image-guided endorectal HDR-BT with 12-24 Gy in 2-3 fractions. Acute and late toxicity of combined EBRT and HDR-BT was recorded according to CTCAE v5.0. Initial tumor response (clinical complete response, cCR, near clinical complete response, ncCR, and incomplete response, IR) and long-term disease control were assessed using clinical examination, endoscopy, and magnetic resonance imaging. RESULTS: Median follow-up was 21 (range, 9-43) months. Six weeks after completion of EBRT + HDR-BT, cCR (n = 6) or ncCR (n = 6) was confirmed in 12/15 patients (80%), 3 patients (20%) had IR. Local regrowth after initial (n)cCR was observed in 4 patients (33%). A total of 4/15 patients (27%) developed distant metastases (2 with IR, 2 with (n)cCR). Most common acute toxicities were mild/moderate proctitis (grade 1-2) in 67%, and mild grade 2 cystitis in 27%. Three patients (20%), of whom two were receiving oral anticoagulation, experienced late grade 3 rectal bleeding, requiring blood transfusion. One patient developed grade 3 rectal ulcer with necrosis treated with rectal amputation. CONCLUSIONS: HDR-BT dose escalation after initial EBRT represents a feasible non-operative treatment option for patients unfit for surgery with promising long-term local control. The incidence of late grade 3 rectal bleeding, especially in patients receiving concomitant oral anticoagulation, requires careful patient selection, and further dose and treatment optimization (as implemented in the upcoming ACO/ARO/AIO-22 trial).