External beam radiotherapy is a widely experimented treatment modality in prostatic cancer. Recently published studies have documented a close dependence of clinical results, in terms of local control and toxicity in particular, on radiation therapy quality. Efforts to improve results of conventional radiotherapy were directed towards the identification of new therapeutic modalities (conformal therapy, fast neutron radiotherapy, neoadjuvant hormonotherapy) as well as towards the optimization of treatment accuracy. In this respect, the following procedures have been particularly effective: 1. the systematic use of CT and retrograde urethrography in PTV definition; 2. immobilization systems which allow a significant reduction in positioning errors; 3. checks before and during treatment by "portal imaging" which allow the identification and correction of a relevant percentage of inaccuracies. The general evolution in treatment planning occurred in recent years has introduced into prostatic cancer radiotherapy new methods and calculation algorithms. While at present the use of new and at the same time complex techniques makes the need for quality assurance of radiation treatments increasingly critical, it is in any case a daily requirement even in most conventional routine treatments.