The treatment outcomes of patients with unresectable rectal cancer are complex, and concurrent chemoradiation therapy is the main treatment option. Radiosensitizers can enhance the effect of localized intratumoral hypoxia, contributing to local control and symptomatic relief. The present study evaluated the feasibility and safety of radiosensitization using hydrogen peroxide combined with radiation therapy (RT) in patients with unresectable rectal cancer. A total of 13 patients with rectal cancer were recruited in the present study. Radiosensitization was performed twice weekly in combination with RT. Gauze soaked in 3% hydrogen peroxide solution was inserted into the anus, ensuring firm contact with the lesion. In total, 45‑65 Gy was delivered in 25‑33 fractions to the whole pelvis from four directions using 10 MV X‑rays 5 days per week. Acute and late adverse events were evaluated 1 and 6 months after the completion of RT. Treatment was well tolerated, with no acute grade 3 or worse events noted, and no patient developed rectal fistula, necrosis, obstruction, perforation, stenosis, ulcer or retroperitoneal hemorrhage. No notable late adverse events, beyond 6 months, were observed at the end of the analysis. All patients experienced pain relief, hemostatic effects and tumor shrinkage. Therefore, the use of a hydrogen peroxide solution‑soaked gauze in the rectum may be a promising option for patients with inoperable rectal tumors. The limitations of the present study are that the patient population was small and the observation time was relatively short. This study was retrospectively registered with the University Hospital Medical Information Network Center (trial registration no. R000061902) on April 21, 2024.

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