The clinical importance of cone beam computer tomography based image guided radiotherapy (CT- IGRT) has not been established. The primary aim of the present trial is to investigate whether CT- IGRT and consequently reduced safety margins reduces the rectal side effects from curative, high dose radiotherapy in prostate cancer. Any impact of the reduced planning target volume in the CT- IGRT arm on biochemical freedom from disease will be evaluated as secondary outcome.

An open randomised phase III trial. The included men will be randomised to receive curative radiotherapy to 78 Gy in 39 fractions with weekly orthogonal position verification and standard safety margins (10-15 mm) or 78 Gy in 39 fractions with daily CT position verification and reduced safety margins (7mm).

Inclusion Criteria:

• Biopsy confirmed adenocarcinoma of prostate
• No evidence of nodal or distant metastases (N0M0)
• Intermediate or high risk based on T stage, PSA level and Gleason score
• Informed consent

Exclusion Criteria:

• Previous treatment for cancer last 5 years, except basal cell carcinoma of skin
• Any previous radiotherapy, except KV or electron treatment of skin tumors outside the pelvis
• Metallic hip joint replacement
• Pre-existing intestinal or genitourinary disease with increased risk of side effects
• Any pre-existing condition making the patient unsuitable for radiotherapy
• Any pre-existing condition making the patient unsuitable for hormonal therapy
• Any pre-existing condition making the patient unsuitable for MRI.
• ALAT, GT, ALP, creatinin > 1.5 x upper normal limit