A phase I clinical trial evaluating the application of hydrogel in reducing rectal dose during cervical cancer brachytherapy.

Purpose: This study represents a prospective phase I clinical research to verify the effectiveness and reliability of hydrogel application in Chinese cervical cancer patients. Materials and Methods: Eight patients were enrolled in the study. After completing intensity-modulated radiotherapy at 50.4 Gy/28 fractions, a 10 mL injection of hydrogel was administered to each patient through the posterior vaginal fornix under CT-guidance. Image-guided brachytherapy under CT or MRI guidance was given with a target dose of 6 Gy in 5 fractions to the high-risk clinical target volume. Rectal, sigmoid colon, and bladder D2cm3 were recorded for each brachytherapy. MRI scans were performed to measure the distance between the rectum and the cervix or tumor, as well as the spacer gel volume. Patients' QLQ-C30 and QLQ-CX24 scores were recorded to assess treatment outcomes, and all adverse events were documented. Results: Among the eight patients, the average D2cc was 60.9 ± 3.4 Gy for the rectum, 64.7 ± 6.8 Gy for sigmoid colon and 77.1 ± 7.4 Gy for bladder, respectively. The distance between the cervix and rectum significantly increased after gel injection. None of the eight patients experienced grade 3 or higher acute toxic reactions during brachytherapy. None patient experienced late rectal toxicity. No adverse events definitively associated with the hydrogel were observed. Patients' subjective quality of life scores did not significantly change before and after gel injection. The reduction ro the volume of the hydrogel were observed during the 24 to 36  weeks after injection. Conclusion: The application of the hydrogel effectively increased the distance between the cervix and rectum in brachytherapy for cervical cancer, limiting the rectal dose without increasing doses to other critical organs. In the short term, no severe adverse events were observed, indicating the safety and reliability of this approach. Further research is warranted to confirm its long-term safety and effectiveness.