Marieke van Son

16 CHAPTER 1 (Figure 5)(84, 85). Adding these two concepts together has led to the idea that even in multifocal prostate cancer, focused treatment of the index lesion alone might control clinical progression of the disease. To enable focal treatment, adequate imaging becomes essential. Herein, the intro- duction of mp-MRI has made it possible to reliably determine the location of cancer foci within the gland(86). However, with multifocal prostate cancer the question remains how to determine the index lesion. Although it has been suggested that it is usually the largest or highest grade lesion, there is also evidence that small, relatively low- grade tumors sometimes harbor the lethal clone(87). Furthermore, mp-MRI has the limitation of often underestimating the size of cancer lesions, necessitating the use of a certain treatment margin to avoid incomplete ablation(88). Therefore, ablation patterns may range from targeting the lesion only (ultrafocal ablation) to treating half the gland (hemi-gland ablation) or three-quarters in a “hockey stick” shape. Different modalities such as cryotherapy, HIFU and brachytherapy are available to achieve focal ablation. Position in the primary setting Despite excellent long-term cancer control rates of contemporary surgery and radio- therapy (especially in low-risk disease), patients face an increased risk of both transient and chronic side-effects affecting their daily living, as described in previous sections. Although the adoption of AS has caused a shift towards reducing (unnecessary) treat- ment, strict inclusion criteria and invasive follow-up protocols restrict the number of patients able or willing to choose such a strategy. Furthermore, ±50% of patients under AS convert to active treatment within 10 years and are therefore still exposed to side-ef- fects(89). Given these disadvantages of whole-gland treatment and active surveillance, focal therapy might be a reasonable treatment option for selected patients. Position in the salvage setting After primary EBRT, the most common site of recurrence is within the prostate gland and/or seminal vesicles(90), with relapses usually occurring at the site of the primary largest (index) lesion(91). Organ-confined, targetable recurrences are eligible for focal salvage treatment, which could be offered as a safer alternative to whole-gland salvage treatment and as a way to prevent or postpone the need for palliative ADT.