Summary 207 Predicting outcomes after focal salvage high-dose-rate brachytherapy for locally recurrent prostate cancer Several focal salvage therapies have been and are currently being investigated, including focal salvage high-dose-rate brachytherapy (FS-HDR-BT). At the Department of Radiation Oncology of the UMC Utrecht, several prospective studies were initiated to investigate the safety and efficacy of MRIguided FS-HDR-BT in patients with locally recurrent prostate cancer after primary radiotherapy. In the PRECISE study, patients were treated in a single fraction with a dose of up to 19.0 Gy. The dose was delivered through catheters that were inserted into the prostate via the perineum. Although this treatment showed very promising results regarding genitourinary (GU) and gastrointestinal (GI) toxicity, initial analysis of oncological outcomes showed a biochemical disease-free survival (bDFS) rate at 2.5 years of just 51%. Patients with a recurrence are then commonly treated with (deferred) ADT. Preferably, the risk of biochemical failure is estimated before patients are treated with this invasive procedure, to be able to counsel patients. In chapter 8, we analysed predictors of biochemical failure in 150 patients treated with MRI-guided FS-HDR-BT. The aim of this study was to find potential predictors for biochemical failure and, in that case, to establish a prediction model that could be used for patient counselling. Biochemical failure was defined according to the Phoenix definition: PSA nadir + 2.0 ng/mL. Two prediction models were created, one that included pretreatment variables only (baseline model, model 1), and one that also included post-treatment variables (model 2). Predictors were selected from a set of predefined candidate predictors using multivariable cox proportional hazards regression analysis. This study showed that at baseline (model 1), age (years), Gross Tumour Volume (cm3), pre-salvage PSA level (ng/mL), and pre-salvage PSA doubling-time (PSADT) (months) were predictive of biochemical failure. In model 2, age (years), presalvage PSA level (ng/mL), pre-salvage PSADT (months), seminal vesicle involvement, post-salvage time to PSA nadir (months), and percentage PSA reduction (ratio between post-salvage PSA nadir and the pre-salvage PSA level) were predictive of biochemical failure. Both models showed reasonable-good discriminative ability. For each model, an interactive web application (nomogram) was created for use in clinical practice. Furthermore, three risk groups were created based on the risk predictions of each model (low-, intermediate-, and high-risk). The estimated 2-year bDFS rates for the low-, intermediate-, and high-risk groups were 84%, 70%, and 31% (model 1), and 100%, 71%, and 5% (model 2). These models could aid patient counselling at baseline and during follow-up. The web applications are easily accessible in the consultation room and this potentially enhances shared decision making. Potentially, these models are also applicable to other salvage treatments, but therefore (external) validation is warranted. Focal SBRT for treatment of local recurrence Because FS-HDR-BT is an invasive treatment – there is a need for spinal anaesthesia and catheters are inserted into the prostate via the perineum – some patients are ineligible. In addition, when fractionated treatment is preferred, a less invasive treatment might be more attractive from both the patient’s perspective and a logistical perspective. A non-invasive alternative treatment could be provided in the form of SBRT. However, to safely deliver a high fractional dose of e.g. 2 x 13.5 Gy or 1 x 19.0 Gy using SBRT, more accurate dose delivery is needed than is possible with conventional 10
RkJQdWJsaXNoZXIy MTk4NDMw