Accumulated bladder wall dose and urinary toxicity 135 registration. In case of registration errors due to large bladder volume differences between MRPV1 and MRPV2-5, a different reference scan was used. Granted the results were satisfying, the case was included for dose-toxicity analyses. Two cases were excluded from dose-toxicity analyses due to mis-registrations near the prostate-bladder interface, which could not be resolved by using a different reference scan. The following bladder (wall) dose parameters were extracted from Doseacc: absolute (cm3) and relative (%) volume receiving 10.0-35.0 Gy (V10-35Gy) in 5.0 Gy bins and 37.0 Gy (V37Gy), mean dose (Dmean) in Gy, and dose (Gy) to the 1.0 and 5.0 cm3 receiving the highest dose (D1cm3 and D5cm3). Urinary toxicity and patient-reported outcome measurements In the UPC study, toxicity was prospectively registered using both physician-reported outcome measurements and PROMs at baseline and during follow-up, including at 1 and 3 months posttreatment. Patients filled out several general and domain-specific, health-related quality of life questionnaires. For this study, we focused on the IPSS. The primary outcome, acute urinary toxicity, was defined as an IPSS increase of ³ 10 points from baseline (IPSS+10) on more than one occasion within three months after treatment, as frequently used in other studies.16,24 Since patients sometimes start with alpha-blocking medication (e.g. tamsulosin) shortly after treatment in case of significant urinary complaints, this might mask an increase in IPSS. Therefore, we assessed a combined outcome: an increase in IPSS of ³ 10 points from baseline and/or start of alpha-blocking medication within 3 months post-treatment. Figure 1 – Exemplary dose distributions (left: transversal slice; right: sagittal slice) for the anatomy on the position verification (PV) scan of fraction 1-5 and the accumulated dose distribution (ACC) on the reference anatomy (PV 1 for this case). The outer and inner bladder wall contours are displayed in black and grey. 7
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