Trial Comparing Irradiation Plus Long Term Adjuvant Androgen Deprivation With GnRH Antagonist Versus GnRH Agonist Plus Flare Protection in Patients With Very High Risk Localized or Locally Advanced Prostate Cancer

Inclusion Criteria: * Histologically confirmed diagnosis of prostate adenocarcinoma * PSA ≥ 10 ng/ml and two of the following 4 criteria: * PSA ≥ 20 ng/ml, * Gleason sum ≥ 8, * cN1 (regional LN with a short axis length \>10mm by CT scan or MRI) or pathologically confirmed lymph nodes (pN1), * cT3-T4 (by MRI or core biopsy) (i.e. If PSA≥ 20 ng/ml then only one of the other 3 risk factors is needed) * M0 by standard imaging work-up (see chapter 6.1.1.1) * Testosterone ≥ 200 ng/dl * Adequate renal function: calculated creatinine clearance ≥ 50 mL/min (Appendix D) Magnesium and potassium within normal limits of the institution or corrected to within normal limits prior to the first dose of treatment. * Patients with prolonged QT-intervals due to prescribed Class IA (quinidine, procainamide) or Class III (amiodarone, sotalol) antiarrhythmic medication must be carefully evaluated for GnRH-agonist or GnRH antagonist use, because these drugs may prolong the QT-interval. * WHO Performance status 0-1 * Age ≥ 18 and ≤ 80 years * Participants who have partners of childbearing potential must use adequate birth control measures, as defined by the investigator, during the study treatment period and for at least 3 months after last dose of study treatment. A highly effective method of birth control is defined as those which result in low failure rate (i.e. less than 1% per year) when used consistently and correctly * Before patient registration/randomization, written informed consent must be given according to ICH/GCP, and national/local regulations. Exclusion Criteria: * Previous use of androgen deprivation therapy (ADT), antiandrogens. 5-alpha reductase inhibitors are allowed if interrupted for more than 6 months prior to entering the study * History of severe untreated asthma, anaphylactic reactions or severe urticaria and/or angioedema. * Hypersensitivity towards the investigational drug * The following biological parameters :AST, ALT, total bilirubin, prothrombin time, serum albumin above upper level of normal range No severe hepatic impairment (Child Pugh C) * History of gastro-intestinal disorders (medical disorder or extensive surgery) that may interfere with the absorption of the protocol treatment. * History of pituitary or adrenal dysfunction * Uncontrolled diabetes mellitus * History of ulcerative colitis, Crohn's Disease, ataxia, telangiectasia, systemic lupus erythematous, or Fanconi anemia. * Clinically significant heart disease as evidence myocardial infarction, or arterial thrombotic events in the past 6 months, severe or unstable angina, or New York Heart Association (NYHA) class III or IV heart disease or cardiac ejection fraction measurement of \< 50 % at baseline * Coronary revascularization (PCI or multivessel CABG), carotid artery or iliofemoral artery revascularization (percutaneous or surgical procedure) within the last 30 days prior to entering the trial * Certain risk factors for abnormal heart rhythms/QT prolongation: torsade de pointes ventricular arrhythmias (e.g, heart failure, hypokalemia, or a family history of a long QT syndrome), a QT or corrected QT (QTc) interval \>450 ms at baseline, or intake of medications that prolong the QT/QTc interval * Uncontrolled hypertension (systolic BP ≥ 160 mmHg or diastolic BP ≥ 95 mmHg); patients with a history of hypertension are allowed provided blood pressure is controlled by anti-hypertensive treatment. * Prior history of malignancies other than prostate adenocarcinoma (except patients with basal cell, squamous cell carcinoma of the skin), or the patient has been free of malignancy for a period of 3 years prior to first dose of study drug(s). Prior history of bladder cancer excludes the patient. * Prior radical prostatectomy (TURP or suprapubic adenomectomy for benign prostatic hyperplasia is allowed) * Prior brachytherapy or other radiotherapy that would result in an overlap of radiotherapy fields * Any contraindication to external beam radiotherapy * Patients with significantly altered mental status prohibiting the understanding of the study or with psychological, familial, sociological or geographical condition potentially hampering compliance with the study protocol and follow-up schedule or any condition which, in the opinion of the investigator, would preclude participation in this trial