This prospective, single-center, single-arm phase II study will evaluate the efficacy, safety, and technical feasibility of an organ-preserving radiotherapy strategy for patients with localized rectal adenocarcinoma who are medically inoperable, decline radical surgery, or are considered technically unresectable without distant metastases.
Participants will receive pelvic external beam radiotherapy followed by high-dose-rate (HDR) endorectal brachytherapy. Concurrent capecitabine may be given during external beam radiotherapy to participants who are considered able to tolerate chemotherapy. During HDR brachytherapy, all participants will be treated using a patient-specific 3D-printed guide template and individualized tungsten-alloy local shielding. The guide template is designed to improve applicator positioning and treatment reproducibility, while the local shielding is intended to reduce radiation exposure to non-target rectal wall.
The study will enroll 50 participants. The primary objectives are to evaluate the 12-month clinical complete response rate and the technical completion rate of the HDR brachytherapy platform. Secondary assessments include organ preservation, local regrowth, survival outcomes, treatment-related toxicity, quality of life, and anorectal function.
Age 18-80 years.
Histologically confirmed rectal adenocarcinoma.
Clinical stage cT2-4, any N, M0.
Patients who are elderly or frail, medically unsuitable for radical surgery, refuse radical surgery, or are considered by a multidisciplinary team (MDT) to have disease for which safe R0 resection is technically difficult.
Distant metastatic disease or disease considered unsuitable for definitive local non-operative treatment.
Prior definitive pelvic radiotherapy.
Intestinal perforation, complete bowel obstruction, uncontrolled active bleeding, or severe active infection.
Anatomical or clinical conditions precluding HDR endorectal brachytherapy or use of the individualized guide template/local shielding platform.
Single group
High-Dose-Rate Endorectal Brachytherapy
RadiationHigh-dose-rate (HDR) endorectal brachytherapy will be delivered as a local dose-intensification component of the organ-preserving treatment strategy for rectal cancer. Brachytherapy will be performed using image-guided, patient-specific treatment planning to optimize target coverage while limiting radiation exposure to adjacent organs at risk. Treatment technique, applicator placement, dose prescription, and fractionation will be performed according to the study protocol.
12-Month Clinical Complete Response Rate
Percentage of participants who maintain a clinical complete response (cCR) at 12 months after completion of study treatment, without local regrowth and without rectal cancer-related salvage resection. Clinical response will be assessed using a composite evaluation including digital rectal examination, endoscopy, and pelvic magnetic resonance imaging.
Technical Completion Rate of HDR Brachytherapy
Percentage of participants who complete all three planned high-dose-rate (HDR) endorectal brachytherapy fractions using the study-specific 3D-printed individualized guide template and tungsten alloy local shielding platform as required by the study protocol.
Overall Clinical Complete Response Rate
Percentage of participants who achieve a clinical complete response (cCR) after completion of study treatment. Clinical response will be assessed using a composite evaluation including digital rectal examination, endoscopy, and pelvic magnetic resonance imaging.
Near-Clinical Complete Response Rate
Percentage of participants classified as having a near-clinical complete response (near-cCR) after completion of study treatment based on composite assessment using digital rectal examination, endoscopy, and pelvic magnetic resonance imaging.
12-Month Organ Preservation Rate
Percentage of participants who remain alive with the rectum in situ and without rectal cancer-related radical salvage resection at 12 months after completion of study treatment.
Local Regrowth Rate
Percentage of participants who develop local tumor regrowth after achieving a clinical complete response or near-clinical complete response during follow-up. Local regrowth will be assessed using digital rectal examination, endoscopy, pelvic magnetic resonance imaging, and other clinically indicated assessments.
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