Interest of Trimodality PET-CT Choline MRI Before Radiotherapy in High Risk Prostate Cancer

Prostate cancer (Pca) is the first human cancer in terms of incidence and the third leading cause of tumor death (56,000 new cases/year in France in 2012 and nearly 9,000 deaths). According to the French Association of Urology 2013, an individual screening based on rectal examination and prostatic specific antigen (PSA) is recommended for men over 50. Ultrasound (US) guided biopsy allows the histological diagnosis and the Gleason score evaluation. For high-risk of prostate Cancer, initial staging is based on pelvic Magnetic Resonance Imaging, abdominal pelvic computed tomography and bone scan. External radiotherapy combined with prolonged hormone therapy is the reference treatment for these cancers. Radiotherapy requires a planning Computed Tomography. Magnetic Resonance Imaging is known to be better for definition of extra-prostatic extensions and prostatic apex. However, its regular use is difficult for the radiotherapy planning. Moreover, Positron Emission Tomography-Computed Tomography with Fluorocholine detects earlier nodal and bone metastasis. Hypothesis: A single planning acquisition in trimodality in radiotherapy position should improve simultaneously the initial staging and the volume delineation for radiotherapy. Main objective: Main objective is to compare volumes delineation (prostatic target and organ at risk) thanks to geometric index (Jaccard, Dice and overlap), got by trimodality and by standard initial staging and planning Computed Tomography. Expected results: Thanks to literature data, it can be expected that prostatic delineation target volume will significantly decrease with Magnetic Resonance Imaging. Furthermore, thanks to Positron Emission Tomography-Computed Tomography with Fluorocholine, radiotherapy planning would be different, detecting 14% of nodal extension and 7% of bone metastasis. Finally, with trimodality the investigators expect a smaller prostate volume and a higher detection of metastatic lymph node or bone metastasis. Then, the investigators expect an improvement of the management of patients by: * Detecting more nodal or bone metastasis and avoiding a useless local treatment by radiotherapy * Improving prostatic target volume delineation and allowing a better protection of organ at risk.