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.

The study is designed as a prospective, randomized, two-armed, single-center phase-II-trial. 60 patients will be included in the study. Patients fulfilling the inclusion criteria will be randomized into one of the two arms, which differ only in the diameter of a tampon used for vaginal dilatation during treatment. All patients will receive standard (chemo)radiotherapy with a total dose of 45-50,4 Gy (single dose 1,8-2 Gy) to the pelvic and inguinal (if required) lymphatic drainage with a boost to the anal canal up to 54-60 Gy (single doses 1.8-2.2 Gy). The primary objective is the assessment of the incidence and grade of vaginal fibrosis 12 months after (chemo)radiotherapy for anal cancer depending on the extent of intrafractional vaginal dilatation. Secondary endpoints are clinical symptoms and toxicity according to the Common Toxicity Criteria (CTC) version 5.0, assessment of clinical feasibility of daily use of a tampon for vaginal dilatation, assessment of the compliance for the use of a vaginal dilatator and quality of life assessed with the EORTC-QLQ30/-ANL27 questionnaires.

Inclusion Criteria:

• Female patient
• Histologically confirmed squamous anal cancer
• Indication for definitive or postoperative radiotherapy
• ECOG 0-2
• Age > 18 years
• Written informed consent

Exclusion Criteria:

• patients refusal or incapability of informed consent
• no vaginal dilatation possible prior to radiation treatment start
• prior pelvic irradiation (if direct field border or even overlap of radiation fields assumed)
• participation in another clinical trial which might influence the results of the DILANA trial
• pregnancy/nursing period or inadequate contraception in women with child bearing potential