Marieke van Son

87 MRI-GUIDED ULTRAFOCAL SALVAGE HDR-BRACHYTHERAPY INTRODUCTION According to current cancer statistics, about one in nine men will be diagnosed with prostate cancer during their lifetime. 1 Approximately 30% of patients are primarily treat- ed with radiotherapy, either with external beam or brachytherapy. 2 Even with modern technical advancements, post-radiation recurrences occur in 10-40% of patients after 10 years of follow-up. 3-5 The benefit of re-treatment must be weighed against a higher chance of (severe) toxicity in the radiorecurrent setting. Furthermore, the impact on quality of life (QoL) has taken a more prominent role in management decisions. Although early recurrences are often confined to the prostate, 6 most patients are treated with systemic androgen deprivation therapy (ADT). 7 This has a temporary sup- pressive effect until the tumor becomes castration-resistant after a median of 3 years. 8 Side-effects range from hot flushes and lowered libido to changes in blood lipids, insulin resistance and loss of bone density. 9 However, due to high toxicity rates, cura- tive whole-gland salvage treatments such as salvage prostatectomy, brachytherapy, cryotherapy or high-intensity focused ultrasound (HIFU) remain unpopular. Common side-effects are urinary incontinence (±10-50%), urethral strictures (±5-25%), fistulas (±2-4%) and impotence (±80-90%). 10 In contrast, focal ablation spares the healthy surrounding tissue, thereby reducing the risk of severe side-effects and associated QoL deterioration. Although with curative intent, the aim of focal salvage treatment is to postpone or potentially avoid the need for palliative ADT. At the UMC Utrecht, we perform ultrafocal ablation with MRI-guided high-dose-rate brachytherapy (HDR-BT). In a previous report, we presented clinical outcomes of the first 17 patients with a median follow-up of 10 months. 11 The current report provides an update on those results, with prospectively collected data from an extended patient group with longer follow-up. METHODS Patient selection Since 2013, MRI-guided ultrafocal salvage HDR-BT has been offered to patients with localized radiorecurrent prostate cancer at the UMC Utrecht. A group of 30 patients with PSA-level ≤10 ng/ml, PSA doubling time (PSADT) ≥12 months, tumor stage ≤T2c on MRI and acceptable urinary function (International Prostate Symptom Score [IPSS]<15) was treated within an institutional review board (IRB)-approved prospective feasibility study. Toxicity rates proved to be very low and after two years of inclusion, experience allowed for extended treatment of patients beyond the initial selection criteria. All un- derwent radiologic disease status assessment with 3T multiparametric (mp)-MRI and 68Ga-PSMA PET-CT (or 18F-Choline PET-CT if treated before 2016) and tumor-targeted (cognitive or MRI-TRUS fusion) prostate biopsies. 24% of patients underwent systematic 5