Marieke van Son

74 CHAPTER 4 Figure 3 – Magnetic resonance imaging (MRI)-compatible robotic implantation device for prostate brachytherapy. A cylindrical weight that is pneumatically driven hits the needle holder to tap a brachytherapy needle into the prostate. Placed between the patient’s legs inside an MRI scanner, the needle can be tracked using live images. Regarding external beam radiotherapy, MRI-guided radiotherapy systems such as the MR-Linac will provide another way to accomplish live MRI-guided intervention. By using online fast MR-sequences for auto-contouring and auto-planning, a full MRI-based online adaptive workflow can be achieved [98]. Changes in anatomy can be accounted for with inter-beam re-planning. This will further reduce the target volume margins needed, reducing normal tissue radiation exposure and thereby decreasing the risk of toxicity. This enables safe dose escalation, potentially in the form of delivering a single ablative dose, which would be of benefit to both patient comfort and hospital logistics. It should however be noted that external beam radiotherapy is inherently less conformal than brachytherapy, and it remains to be seen whether this treatment modality will be suitable for focal treatment in the recurrent prostate cancer setting. CONCLUSION Localized radiorecurrent prostate cancer seems susceptible for focal salvage treatment. Treating the tumor while sparing the surrounding healthy tissue leads to a reduction of treatment-related side effects, where whole-gland salvage treatments or palliative ADT are often less well-tolerated. Focal salvage therapy thereby provides an intermediate step between primary curative treatment and (if necessary) palliative hormonal treatment. Diagnostic innovations have led to more adequate patient selection in terms of exclusion of metastatic disease and accurate tumor targeting. This is a constant developing field, as new diagnostic techniques are warranted to provide greater insight into prostate tumor profiling. With MRI-guidance, focal treatment becomes more and more precise, especially with emerging technologies enabling live and online adaptive MRI-guided radiotherapy.