Marieke van Son

72 CHAPTER 4 Figure 2 – Flow chart for decision-making before and after focal salvage treatment of localized radiorecurrent prostate cancer. *As proposed by Delphi consensus study among 18 experts in the field of salvage brachytherapy for radiorecurrent prostate cancer (conducted by UroGEC group of GEC-ESTRO) [88]. Future prospects regarding MRI-guided radiotherapy It is clear that accurate targeted ablation requires precise localization of the recur- rent prostatic lesion. Over the years, the use of (mp-)MRI for treatment planning has substantially increased. The superior resolution of soft tissue enables more accurate delineation of the tumor volume and organs at risk [91]. New developments such as ultra-high field MRI with 7T systems have the potential to enhance the spatial resolu- tion even further [92]. Although it seems that 7T T2- and diffusion-weighted imaging deliver clinically adequate anatomical images within acceptable acquisition times, there are still several technical challenges to overcome before a 7T mp-MRI protocol for the prostate can be achieved [93]. Imaging developments are not only used for the treatment planning phase, but are also increasingly incorporated into the treatment itself. Currently, MRI-guidance during treatment can be achieved using image registration of pre-operative MR-images (1.5T or 3T) with intra-operative TRUS-images (MRI-TRUS fusion). With this technique,