Proton Versus Photon Therapy in Anal Squamous Cell Carcinoma

Inclusion Criteria: 1. The patient must be at least 18 years old 2. Histologically confirmed, previously untreated squamous cell carcinoma (p16-positive or p16-negative) of the anal canal (ICD-O-3 C21), i.e. cancer of the perianal skin without connection to the anal canal are not included. The patients may have primary tumour, regional nodes, metastasis (TNM)-stage T2 (\>4 cm) -4,N0-1c,M0 (UICC 8th edition). 3. World Health Organisation/Eastern Cooperative Oncology Group (WHO/ECOG) performance status 0-1 4. The patient must be able to understand the information about the treatment and give a written informed consent. Exclusion Criteria: 1. Patients with cancer of the perianal skin without involvement of the anal canal (ICD-O-3 C44.5) are not eligible. 2. Patient judged to have any other treatment than radiotherapy with concomitant chemotherapy as the preferred treatment 3. Concomitant or previous malignancies. Exceptions are, adequately treated basal cell carcinoma or squamous cell carcinoma of the skin or, other previous malignancy with a disease-free interval of at least 5 years. 4. Two or more synchronous primary cancers in the pelvic region at time of diagnosis 5. Previous radiotherapy, surgery or chemotherapy that may interfere with the planned treatment for the present disease, as judged by the investigator. 6. Co-existing disease prejudicing survival (expected survival should be \>2 years). 7. Pregnancy or breast feeding 8. When prosthetic materials (e.g. hip prostheses) are present close to the target volume it must be considered if this may introduce uncertainties in dose calculations that precludes especially, proton therapy. 9. Patients with pacemaker/ICD are not eligible.