Intrafractional Vaginal Dilation in Anal Cancer Patients Undergoing Pelvic Radiotherapy

A commercially available vaginal dilator set will be used as measuring device. The grading of vaginal stenosis will be determined as difference of the diameter of vaginal dilator to the baseline. A reduction of the diameter of \<20% is defined as vaginal stenosis Grade 1, a reduction of 20-35% as Grade 2, a reduction of \>35-49% as Grade 3 and a reduction \>/=50% as Grade 4. The investigators hypothesize that the rate of vaginal stenosis Grade 1 or higher 12 months after radiotherapy is lower in the group using extended vaginal dilation during radiotherapy (Arm A). Rates of vaginal stenosis of 50% have been observed in previous patient collectives and the investigators hypothesize that a reduction to 25% is possible in the experimental group.