Marieke van Son

53 MRI-GUIDED ULTRAFOCAL HDR-BRACHYTHERAPY DISCUSSION The main goal of ultrafocal ablation of localised prostate cancer is to reduce treat- ment-related side-effects and thereby maintain QoL while not compromising tumour control. The medium-term results of this study show that it is feasible to treat with limited toxicity and minimal impact on QoL. However, 70% BDFS at 4 years is an unfa- vourable tumour control outcome, which needs comprehensive evaluation to assess the position of ultrafocal HDR-brachytherapy in the primary prostate cancer setting. Toxicity and QoL outcomes were mostly in line with our previous report, with no treatment-related severe GU or GI toxicity and a minor impact on patient-reported QoL. A distinct result was a clear downward trend in erectile function, as reflected by deteriorating IIEF scores and CTCAE-graded ED scores, with more patients experiencing grade 2-3 ED during follow-up compared to the previous analysis. The IIEF classifies ED into five categories: severe (5-7), moderate (8-11), mild to moderate (12-16), mild (17-21), and no ED (22-25). Defining potency as satisfactory capacity of having an erection, this may involve submaximal rigidity or capability to sustain the erection, corresponding to IIEF scores >17 as a reasonable cut-off point. Within our study group, 16 patients had pre-treatment IIEF score >17 (initial potency), of which 8 had IIEF scores below 17 at last follow-up (50% new onset impotence). The decrease of erectile function might in part be attributable to radiation sensitivity of the neurovascular bundles, although the relation between neurovascular bundle dose and erectile dysfunction remains hypothetical(15). With 43% of our patients having bilateral (T2c) disease, this potentially could have led to a higher dose burden on the neurovascular bundles. However, we do not have dosimetry data and there is a lack of established delineation guidelines for the neurovascular bundles(16). Moreover, part of the deterioration could be explained by the natural course of developing ED with increasing age. Further evaluation of QoL showed only transient deterioration of general health (RAND-36 subdomains). Patients reported more tiredness, but at the same time im- provement of emotional and cognitive functioning (QLQ-C30). There was a transient increase in urinary symptoms and a decrease in sexual activity (although relatively stable sexual functioning), but no bowel symptoms (PR-25). To our knowledge, no other FT studies have reported such extended QoL analyses. This provides new and detailed insight into the domains that are affected. Direct comparison of our data with others is difficult as no other literature on ultra- focal HDR-brachytherapy is available. When comparing our results to a small focal Iodine-125 brachytherapy series (n=21), contrasting results are shown with stable IIEF at a mean score of 20 after 12 months follow-up(17). Possible explanations could be their smaller target volumes or substantially lower patient age (mean 62 versus median 71 in our cohort). It is also possible that HDR-brachytherapy inherently has a larger influence on erectile function than Iodine-125 brachytherapy. Similar to our report, this study showed an early temporary increase in IPSS. Another small study on ultrafocal 3