Dynamic changes and outcomes of magnetic resonance imaging in radiotherapy-related rectal injury in cervical cancer

Background: To observe dynamic changes of rectal injury in patients with locally advanced cervical cancer during curative pelvic radiotherapy using magnetic resonance imaging (MRI), and to explore non-invasive radiological methods for assessing radiation-induced rectal injury (RRI). Methods: A retrospective analysis was conducted on pelvic MRI images from 56 patients with locally advanced cervical cancer who underwent radical radiotherapy. MRI scans were conducted at four key stages: before radiotherapy, two weeks after starting external irradiation, upon completing external irradiation, and at the conclusion of brachytherapy. Thickness of the intestinal wall from the anorectal region to the sigmoid take-off at each scanning level was measured by RadiAnt DICOM Viewer software, and the average rectal wall thickness was calculated. Statistical analysis was performed using SPSS 26. Results: Out of the 56 patients undergoing pelvic radiation therapy, 30 (53.6%) reported symptoms of rectal injury, including diarrhea, increased frequency of stools, loose stools, abdominal pain, tenesmus, and difficulty in defecation, typically appearing during the 3rd to 5th week of treatment. Medication-preserved enemas were administered in the 5th week of radiotherapy and at the beginning of brachytherapy. In symptomatic patients, rectal wall thickness at two weeks of radiotherapy (7.76 ± 0.96 mm) was significantly greater than that before radiotherapy (6.98 ± 0.77 mm) (p < 0.01). Thickness continued to increase during external irradiation, reaching its peak at the end of external irradiation (7.99 ± 0.83 mm), followed by a decrease at the end of brachytherapy (7.31 ± 0.81 mm), which was significantly reduced compared with end-of-external-irradiation values (p < 0.01). Conclusions: Patients with locally advanced cervical cancer undergoing pelvic radiotherapy exhibit significant early and time-dependent rectal imaging changes prior to the onset of evident clinical symptoms of RRI. MRI may serve as a sensitive diagnostic tool for the early detection and prediction of radiation-induced rectal injury.