Anorectal function and radiation dose to pelvic floor muscles after primary treatment for anal cancer

Abstract

Background and purpose: Chemoradiotherapy is the primary treatment for localized anal cancer (AC). This treatment offers high rates of cure and organ preservation. Radiotherapy can however, result in late persisting anorectal dysfunction, with anal incontinence, urge and clustering. Correlation of radiation doses to pelvic substructures and functional outcome is not well described in AC. We correlated patient reported anorectal function to radiation doses to sphincters and pelvic floor muscles.

Materials and methods: Patients treated with (chemo)radiotherapy for AC were asked to fill out LARS (lower anterior resection syndrome) questionnaires at follow-up. We compared patients with no LARS (score 0-19) and patients with major LARS (30-42) as well as individual LARS questions to specific radiation doses to sphincters, levators and puborectal muscles.

Results: Thirty-six patients were included, 18 with no LARS and 18 with major LARS. Gender, age, TNM stage, PTV, chemotherapy, time to LARS score (mean 660 and 749 days) were comparable between the two groups. LARS symptoms, occurring at least once per week, were reported between 25-55.7%, and poorer LARS outcome was associated to worse quality of life. Dose to sphincter complex (Dmean, V50Gy and D90%) differed significantly between patients with no and major LARS (p = 0.048, 0.035 and 0.02 respectively). Further, D90% to the sphincter complex was significantly higher in patients who had accidental leakage of stool, (p = 0.044).

Conclusion: Patients treated with (chemo)radiotherapy for AC show high frequency of patient reported anorectal dysfunction. Specific doses to the sphincters could become a useful predictor of anal incontinence and major LARS and incorporated into future radiotherapy planning studies.

Keywords: Anal cancer; Dose volume parameters; PRO; Radiotherapy.