Research Objective and Principle: To evaluate the effectiveness of Bergmann enema in preventing acute radiation-induced rectal injury in patients with rectal cancer, thereby providing a basis for treatment options for potential radiation-induced rectal injury patients, aiming for adoption by international guidelines.

Primary Objective: Incidence of grade 2 or higher radiation-induced rectal injury.

Secondary Objectives: Severity of radiation-induced rectal injury, completion rate of short-course radiotherapy, safety of Bergmann enema, quality of life, pathological complete response (pCR) rate.

Study Design: Prospective, single-center, single-arm study.

Study Population and Expected Enrollment: Patients with rectal cancer undergoing short-course radiotherapy, expecting to enroll 40 patients.

Trial Duration: From December 2025 to December 2026.

Intervention: Patients will receive Bergmann enema (30 ml) once daily from the start of radiotherapy until the 10th day after the end of radiotherapy.

Statistical Hypothesis: Based on previous reports, the incidence of acute radiation-induced rectal injury is 80%, and it is expected that Bergmann enema preventive treatment can reduce it to 50%. The sample size was estimated using a formula designed to calculate single-group rate, with a set at 0.05 and a power of 80%. The study aimed to enroll at least 36 patients. Considering a dropout rate of 10%, at least 40 patients need to be included.

Inclusion Criteria:

1. Aged 18 to 75 years, regardless of gender;
2. Fully understand this study and voluntarily sign the informed consent form, able to comply with the study protocol and complete all trial procedures;
3. Patients with pathologically confirmed mid-lower rectal cancer;
4. Undergoing short-course pelvic radiotherapy (total dose of 25-35Gy in 5.0-7.0 fractions over 5 consecutinve days);
5. Eastern Cooperative Oncology Group (ECOG) score of 0-1, with an expected survival time of more than 6 months;
6. Assessment by the attending physician and researcher indicates that vital organ function can tolerate the treatment risks.

Exclusion Criteria:

1. Severe comorbidities, including uncontrolled stable medical diseases after treatment, or a history of neurological or psychiatric disorders (such as dementia or epilepsy), making them unsuitable for radiotherapy;
2. Patients who have received pelvic radiotherapy;
3. Presence of malignant pleural effusion or malignant abdominal effusion, or accompanied by bowel obstruction;
4. Pregnant or breastfeeding women;
5. Patients expected to undergo major surgery during the study period;
6. Participation in other clinical trials within 4 weeks prior to enrollment;
7. A history of alcohol abuse, drug use, or substance abuse within the past year;
8. Severe allergic constitution, or allergy to Bergmann;
9. Inability to cooperate with the enema;
10. Subjects deemed unsuitable for participation in this trial for other reasons by the researcher.