Prostate cancer

In this chapter, we aim to give insights into questions arising during contouring of the target volumes and organs at risk for patients with prostate cancer either in the definitive or in the postoperative setting. Obviously, target volume definition is different in both settings. With the increasing use of hypofractionated or even ultrahypofractionated concepts, target volume delineation becomes more and more important. Multiparametric MRI and PSMA-PET/CT are implemented in the contouring process of the GTV. The CTV consists of the prostate and seminal vesicles according to the patients' risk group adding a customized margin. The appropriate CTV for each patient with localized PCa should be defined under consideration of the individual risk group and the used fractionation regimen. The CTV-PTV margin is institution specific and depends on the frequency of image verification among other factors. The NRG Oncology genitourinary core committee consensus atlas for pelvic nodal contouring is a valid reference for pelvic lymph node regions. In the postoperative setting, the prostate bed with or without a boost to a macroscopic recurrence and pelvic or para-aortic lymphatics with or without a boost to positive lymph nodes/regions can be part of the target volume. It is important to have all clinical information available in order to customize the target volume to the individual patient's situation. MRI and PSMA-PET/CT are used in salvage RT for staging purposes as well as to help in target delineation and for dose escalation purposes. Although controversies between different guidelines exist, the most important points all guidelines agreed on are that CTV should encompass the prostate and the seminal vesicle bed at risk of harboring microscopic disease, the CTV should include areas of involved resection margins, and the vesicourethral anastomosis and periurethral tissue must be covered in the CTV. Again, the CTV-PTV margin is dependent on institution-specific guidelines and should be between 6 and 10 mm.