Purpose: To investigate long-term changes in the rectal mucosa after curative external beam radiation therapy in the treatment of prostate cancer.
Methods and materials: In the Scandinavian Prostate Cancer Group 7 trial, 880 men with locally advanced prostate cancer were randomized to hormonal therapy alone versus hormonal therapy plus radiation therapy to 70 Gy. A subcohort from this trial being randomized at our center (n=178) was invited to a study on late anorectal side effects during 2003-2005, approximately 5 years after treatment, including measuring health-reported quality of life and physician-assessed toxicity score by the Late Effects Normal Tissue Task Force/Subjective, Objective, Management, Analytic (LENT/SOMA) and European Organization for Research and Treatment of Cancer/Radiation Therapy Oncology Group score. Sixty-seven patients had a rectal mucosa biopsy. Sixty-four biopsies were included in the final analysis, of which 33 patients were randomized to hormonal treatment and 31 to hormonal treatment plus radiation therapy. The presence of fibrosis, number of capillaries, and lymphocyte infiltration was then evaluated by light microscopy.
Results: The group receiving radiation therapy had significantly higher LENT/SOMA and function/bother scale scores than the group that only received hormonal treatment, but there was no significant difference in the presence of fibrosis, ectasia, number of capillaries in the lamina propria, or lymphocyte infiltration between the groups.
Conclusion: Radiation therapy to 70 Gy to the prostate does not induce long-term microscopic mucosal changes in the rectum 5 years after treatment. This is in contrast to the general assumption that structural changes, including fibrosis, seen after radiation therapy include the mucosa. We speculate that the main late effects of radiation therapy on the structure of the rectum are located in the deeper layers of the rectal wall than the mucosa.
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