The primary objective of this trial is to examine the value of prophylactic versus therapeutic breast radiotherapy in Casodex monotherapy induced gynaecomastia and/or breast pain. Patients will receive either prophylactic radiotherapy to the breast at a dose of 12Gy (as two fractions of 6 Gy in consecutives days), or will not receive any radiotherapy prior to commencing CASODEX 150mg monotherapy.