Marieke van Son

108 CHAPTER 6 7014) or outside the scope of a study protocol, including patients with higher-risk disease characteristics, such as seven patients with a solitary lymph node or bone metastasis who received upfront stereotactic radiotherapy. For study patients, trial inclusion criteria were PSA <10 ng/ml, PSA doubling time (PSADT) >12 months and MRI tumor stage ≤T2c (NTR 6123) or PSA ≤20 ng/ml, PSADT ≥9 months and MRI tumor stage ≤T3b (NTR 7014). All patients (on- or off-protocol) were prospectively followed in the same manner. Informed consent was obtained from all study patients. For patients treated off-protocol, the IRB waived the requirement for informed consent. For this report it was pragmatically chosen to analyze the first 100 treated patients, since they all had at least three months post-treatment follow-up before the start of the analysis. Treatment Using 3T multiparametric MRI (T2-weighted, diffusion-weighted and dynamic contrast enhanced sequences) and 68Ga-PSMA or 18F-Choline PET-CT, we delineated the gross tumor volume (GTV), clinical target volume (CTV, defined as five-millimeter margin around GTV) and organs at risk (OARs: bladder, rectum, and urethra). The rectum was delineated between the level of the sigmoid fold and the anal region, the bladder was delineated within the available field of view and the urethra was delineated one slice above and one slice under the prostate (sagittal plane). No PTV-margin was applied. Under the guidance of rigidly fused MRI/transrectal ultrasound images, MR-compatible catheters were transperineally inserted in and around the CTV. A subsequent 1.5T MRI scan was used for catheter reconstruction and adjustment of delineations. Radiation goal was to administer a single dose of 19 Gy to 95% of the CTV. Dosimetry constraints were D1cc <12Gy for the bladder and rectum and D10% <17.7Gy for the urethra. With the radiation dose fully targeted at the CTV instead of a quarter or half of the gland, this treatment is generally described as ultrafocal. Outcome assessment HR-QoL was investigated using the EORTC QLQ-PR25 questionnaire, which was specif- ically designed for use among prostate cancer patients(11). Questionnaires were sent out before treatment and after 1, 3, 6, 9, 12, 18 and 24 months, and yearly thereafter. The respective domains are urinary symptoms (9 items), bowel symptoms (4 items), sexual activity (2 items) and sexual functioning (4 items). As ADT was not part of this treatment, we did not analyze the domain hormonal treatment-related symptoms. For each item, patients were asked to indicate the extent to which they had experienced symptoms or problems during the past week (1: not at all, 2: a little, 3: quite a bit, 4: very much). Domain scores were linearly transformed to a 0-100 scale if at least half of the items in the domain were answered. Higher scores either indicated more symptoms (urinary and bowel domains) or higher levels of functioning (sexual domains). For the QLQ-PR25 questionnaire, no threshold value has been determined as the minimal clinically important difference in scores. In concordance with the QLQ-C30