This chapter reviews the use of PET/CT in the radiation therapy planning of prostate cancer. The successful history of PET imaging in prostate cancer is rather short, maximally two decades, and its use in routine practice is even shorter, maximally 5 years. Because of approval of new potential imaging agents, prostate cancer staging with PET has become increasingly well-adapted. This had led to better and earlier diagnosis which requires precise treatment. Oligometastatic or oligorecurrent disease can be treated with modern targeted therapies, including multiple external beam radiation therapy methods. Here, the history of PET/CT in radiation therapy planning has been reviewed in local or more disseminated disease tracer by tracer, including 11C/18F-choline, 11C-acetate, 68Ga-PSMA, multiple 18F-PSMA tracers, 18F-FACBC, and 18F-fluoride. Additionally, a few cases who have been successfully treated with own PET based radiation therapy planning are presented, both in primary and oligorecurrent situation.