title: An evaluation of our experience in position verification of catheters used for interstitial high-dose-rate brachytherapy of solitary bladder tumors.
abstract: The goal of this study was to verify the position of catheters used over 4 days for brachytherapy of solitary bladder tumors.
  
  
  
  The study covered three phases. Shifting of catheters was studied using daily position verification CT scans of 20 patients. The possibility to omit the CT scan on Day 2 by adding a loading margin of 4 mm on each side was studied using data of 5 patients. Whether the Day 4 verification CT scan could be omitted if this margin was used, was studied for another group of 10 patients, comparing the Day 3 treatment plan to the Day 4 CT scan.
  
  
  
  An average catheter shift on Days 2, 3, and 4 of, respectively, -0.3 mm (-8 to 10 mm), -0.5 mm (-14 to 10 mm), and -0.1 mm (-16 to 28 mm) was found over the measurements at both sites of the catheter. Including only shifts causing underdosing of the clinical target volume (CTV), the average shift on Days 2, 3, and 4 was, respectively, -3.6 mm (-1 to -8 mm), -5.4 mm (-1 to -14 mm), and -5.3 mm (-1 to -16 mm). After adding a loading margin, the CTV was covered on Day 2; however, the margin was not sufficient for Days 3 and 4. On Day 4, in 2/10 patients, the CTV was not completely covered. In 5/10 patients, an increased 200% isodose volume was found.
  
  
  
  Position verification is necessary in bladder brachytherapy. If a 4-mm margin on each side of the loading pattern was added, position verification on Day 2 could be omitted. The verification CT scan of Days 3 and 4 is still necessary.
authors.affiliation: Department of Radiation Oncology, Radiotherapiegroep, Arnhem, The Netherlands. Electronic address: s.bus@radiotherapiegroep.nl.
authors.forename: S J E A
authors.initials: SJEA
authors.lastname: Bus
authors.affiliation: Department of Radiation Oncology, Radiotherapiegroep, Arnhem, The Netherlands.
authors.forename: N G
authors.initials: NG
authors.lastname: Leus
authors.affiliation: Department of Radiation Oncology, Radiotherapiegroep, Arnhem, The Netherlands.
authors.forename: B J
authors.initials: BJ
authors.lastname: Oosterveld
authors.affiliation: Department of Radiation Oncology, Radiotherapiegroep, Arnhem, The Netherlands.
authors.forename: M P R
authors.initials: MPR
authors.lastname: Van Gellekom
authors.affiliation: Department of Radiation Oncology, Radiotherapiegroep, Arnhem, The Netherlands.
authors.forename: G J M
authors.initials: GJM
authors.lastname: van de Loop
authors.affiliation: Department of Radiation Oncology, Radiotherapiegroep, Arnhem, The Netherlands.
authors.forename: E M
authors.initials: EM
authors.lastname: van der Steen-Banasik
mesh_terms: D001918:Brachytherapy / Q000295:instrumentation / Q000379:methods*; D057785:Catheters; D005548:Foreign-Body Migration / Q000000981:diagnostic imaging*; D006801:Humans; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D013997:Time Factors; D014057:Tomography, X-Ray Computed; D001749:Urinary Bladder Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*
keywords: Bladder cancer; Brachytherapy; Catheter displacement; High-dose-rate; Position verification; Radiation therapy