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

The initial staging of locally advanced prostate cancer is made with Computed Tomography scan (CT), Magnetic Resonance Imaging (MRI), and bone scan (BS). For this type of cancer, reference treatment is radiotherapy combined with hormone therapy. The added value of MRI in the delineation of volumes for radiotherapy is known, especially for the definition of extra-prostatic extensions and prostatic apex. However, its regular use is difficult. Indeed, acquisition of Magnetic Resonance Imaging parameters for diagnostic are not adapted to be fused with the planning Computed Tomography. The literature shows that Positron Emission Tomography-Computed Tomography with Fluorocholine is better in terms of diagnostic performance compared to bone scan for bone metastases and to pelvic Magnetic Resonance Imaging for nodal extension. It would therefore improve staging for these patients with a high risk of locoregional and metastatic invasion even if its use is currently not recommended in the initial staging. Thanks to Magnetic Resonance Imaging acquisition parameters adapted to Radiotherapy and additional functional information, an acquisition in tri-modality Positron Emission Tomography/computed Tomography/ Magnetic Resonance Imaging could have an impact on the volumes definition for radiotherapy or even on the therapeutic strategy. The aim of the study is to evaluate the volume modifications obtained on the trimodality evaluation, compared to the standard initial staging (geometric comparison). In addition, it would be a preliminary study for a project using Prostate-specific membrane antigen (PSMA) in trimodality, and / or for a therapeutic interventional study.