Marieke van Son

109 QOL AFTER ULTRAFOCAL SALVAGE HDR-BRACHYTHERAPY questionnaire (HR-QoL of cancer patients in general, similar scoring range 0-100), we defined a change of ≥10 points as a clinically relevant difference(12). Statistical analysis To estimate average HR-QoL trends over time, a mixed effects model for repeated measures was made for each domain. Differences between baseline HR-QoL scores and follow-up time points were tested by adding time as a categorical variable to the mixed effects model. The significance level for HR-QoL change was set at p=0.01, taking into account multiple testing. Trends were graphically displayed using the group least squares means and their standard errors. Secondly, we explored potential predictors of change in HR-QoL within each model. This was only analyzed for the domains that showed clinically relevant change. We hypothesized that age, baseline HR-QoL score, T-stage of the tumor (as scored by the AJCC TNM eighth edition staging manual), size of the CTV and dose to the respective organs at risk (OAR) are potential factors predicting HR-QoL change. For the sexual domain, we also included previous use of ADT and dorsolateral location of the tumor. Assessment of the relation between these predictors and change in HR-QoL was per- formed in a multivariable model, calculating odds ratios and their 95% confidence in- tervals (CI). Predictors with p-values <0.05 were considered statistically significant. Statistical analyseswere performedwith R statistical software (version 3.5.1; the R foun- dation for Statistical Computing, Vienna, Austria) and IBM SPSS statistics (version 23.0). RESULTS The median follow-up time was 20 months (interquartile range [IQR] 13-30 months). Questionnaire response rates were between 72% (3 months) and 100% (36 months), with a mean response rate of 86%. At baseline, patients reported mild urinary symptoms (median score 12, IQR 8-21) and negligible bowel symptoms (median score 0, IQR 0-8). Sexual activity was at a baseline median score of 67 (IQR 50-83), and sexual function- ing at median 50 (IQR 42-67). The median CTV D90% was 21.43 Gy (IQR 19-21.5), with a median of 9 brachytherapy catheters used for the implant (IQR 8-11). A summary of baseline patient and tumor characteristics is displayed in Table 1. 6