Differences in Radiation Dosimetry and Anorectal Function Testing Imply That Anorectal Symptoms May Arise From Different Anatomic Substrates

Purpose To explore the influence of functional changes and dosimetric parameters on specific incontinence-related anorectal complaints after prostate external beam radiotherapy and to estimate dose–effect relations for the anal wall and rectal wall. Methods and Materials Sixty patients, irradiated for localized prostate cancer, underwent anorectal manometry and barostat measurements to evaluate anal pressures, rectal capacity, and rectal sensory functions. In addition, 30 untreated men were analyzed as a control group. In 36 irradiated patients, the anal wall and rectal wall were retrospectively delineated on planning computed tomography scans, and dosimetric parameters were retrieved from the treatment plans. Functional and dosimetric parameters were compared between patients with and without complaints, focusing on urgency, incontinence, and frequency. Results After external beam radiotherapy, reduced anal pressures and tolerated rectal volumes were observed, irrespective of complaints. Patients with urgency and/or incontinence showed significantly lower anal resting pressures (mean 38 and 39 vs. 49 and 50 mm Hg) and lower tolerated rectal pressures (mean 28 and 28 vs. 33 and 34 mm Hg), compared to patients without these complaints. In patients with frequency, almost all rectal parameters were reduced. Several dosimetric parameters to the anal wall and rectal wall were predictive for urgency ( e.g., anal Dmean >38Gy), whereas some anal wall parameters correlated to incontinence and no dose–effect relation for frequency was found. Conclusions Anorectal function deteriorates after external beam radiotherapy. Different incontinence-related complaints show specific anorectal dysfunctions, suggesting different anatomic and pathophysiologic substrates: urgency and incontinence seem to originate from both anal wall and rectal wall, whereas frequency seems associated with rectal wall dysfunction. Also, dose–effect relations differed between these complaints. This implies that anal wall and rectal wall should be considered separate organs in radiotherapy planning.