Marieke van Son

65 FOCAL SALVAGE TREATMENT: A NARRATIVE REVIEW remain unpopular amongst treating physicians, with only 2% of patients receiving any form of salvage curative treatment. The other 98% receives ADT, either immediately or deferred [36]. These patterns are also observed in large national databases, such as the Cancer of the Prostate Strategic Urological Research Endeavor (CaPSURE) database from the U.S. [37]. Focal treatment of radiorecurrent prostate cancer With recurrences often being localized and unifocal (mainly at the ‘index lesion’ site), a salvage treatment directed solely at the recurrent tumor lesion seems rational. Espe- cially considering the narrow therapeutic ratio (treatment efficacy versus treatment-re- lated toxicity) in the recurrent setting, focal treatment provides a promising alternative: a second chance at achieving local control, with minimal burden to the patient in terms of side-effects. DIAGNOSTIC ASSESSMENT Excluding metastatic disease The success of focal salvage treatment starts with adequate exclusion of metastatic disease. More dated series of whole-gland salvage treatments often show substantial failure rates due to inadequate pre-treatment diagnosis of metastases. For example, technetium-99m bone scintigraphy was often used to exclude bone metastases, which only achieves acceptable diagnostic accuracy in patients with higher-risk disease characteristics (PSA>20, Gleason ≥8) [38]. Furthermore, studies regarding computed tomography (CT) and/or magnetic resonance imaging (MRI) for nodal disease staging have demonstrated poor diagnostic accuracy [39], since lymph node diameter and morphology are inadequate predictors for nodal invasion. Positron-emission com- puted tomography (PET/CT), however, is recommended as the standard diagnostic modality to assess metastatic disease in the recurrent setting. It offers the advantage of concurrently evaluating bony and nodal metastatic disease. Different PET tracers have been used, with choline and fluoride as originally most abundant [40-42]. Negative predictive values of up to 100% have been reported, although the range observed in the reported literature is substantial. Thus far, the most promising PET-technique seems to be (68)Ga prostate-specific membrane antigen (PSMA)-PET/CT, with a radiotracer binding more specifically to a cellular protein overexpressed on 95% of prostate cancer cell-membranes. High diagnostic accuracy is attained for both intra-prostatic lesions as well as lymph node and bone metastases, even at low PSA-values (<2 ng/ml) [43,44]. Available since 2013 [45], PSMA-PET/CT has quickly become a routine form of target- ed molecular imaging in countries across Asia, Australia, and Europe [46]. Currently, diffusion-weighted whole-body MRI is also being investigated for assessment of bone metastases in the recurrent setting, although PET/CT seems superior [47,48]. 4