The trial is to explore new and effective techniques in the treatment of prostate cancer and evaluate the role of PET-CT / MRI played in radiotherapy. Intensity modulated radiation therapy(IMRT) is adopted with all patients and the efficacy assessment for the prostate cancer will be examined with PET / CT or CT in three months after radiotherapy.

All participants judged to have prostate cancer with stage Ⅲ-Ⅳand considered able to conduct radiotherapy. 180 patients will be enrolled in the trial and randomly divided into three groups. Three arms are respectively treated with CT、18F-FDG PET/CT、18F-FDG PET/MRI. The images were passed in three-dimensional treatment planning system, using software manually fusion and reconstruction of PET and CT. All patients adopt IMRT for the radiotherapy with 70Gy-80Gy. Three months after radiotherapy, solid tumer size for the prostate cancer will be assesed with PET / CT or CT. Early radiation reactions are evaluated by the United States RTOG (RTOG) acute response evaluation criteria, and late radiation reaction are evaluated with RTOG and the European Radiation Therapy Oncology Organization (EORTC). Before and after radiotherapy treatment,the tumor-associated marker of PSA will be monitored and the patients are regularly followed-up in the next three years.

Inclusion Criteria:

• Patients with pathologically confirmed prostate cancer
• Staged with Ⅲ-Ⅳ prostate cancer
• Aged from 18 to 65 years old
• Quality of life score (Karnofsky performance score) > 70
• No distant metastasis
• No serious internal diseases may affect the treatment plan
• No previous history of prostate radiation therapy
• Patients must be able to understand and be willing to sign a written informed consent document.

Exclusion Criteria:

• Distant metastasis
• Accompanied by other malignancies
• Previous history of prostate radiation therapy
• Pregnant or lactating women
• History of allergic reaction to iodinated, non-iodinated, and/or gadolinium contrast agents
• Liver and kidney dysfunction
• Pacemaker or other metallic devices that would prevent MRI imaging from being performed
• Patients quit during the treatment or violate of the study protocol caused by other factors
• Any reason that, in the option of the investigator, contraindicates that the patient participates in the study