title: The impact of prostate volume changes during external-beam irradiation in consequence of HDR brachytherapy in prostate cancer treatment.
abstract: OBJECTIVE
  To evaluate prostate volume changes during external-beam irradiation in consequence of high-dose-rate (HDR) brachytherapy in prostate cancer treatment.
  
  
  METHODS
  20 patients who underwent radiotherapy for prostate cancer were included in this prospective evaluation. All patients had a computed tomography (CT) scan for planning of the external-beam irradiation and additional scans after each HDR brachytherapy. For the planning target volume (PTV), a safety margin of 10 mm was added to the clinical target volume (CTV) in each direction. The prostate volume measured in the planning CT was compared with the prostate volumes measured after HDR brachytherapy and, subsequently, the change of prostate volume was calculated. Volume changes which resulted in differences of the prostate radius of > 5 mm for the CTV were defined as a reason for a new treatment-planning procedure for the patient.
  
  
  RESULTS
  Taking all patients together, prostate volumes before HDR, 1 day and 4-6 days after the first HDR treatment, as well as 1 day and 4-6 days after the second HDR treatment were in median 37.7 cm(3), 37.6 cm(3), 38.2 cm(3), 39.3 cm(3), and 40.5 cm(3), respectively. In none of the patient, a volume change resulted in a change of the prostate radius of > 5 mm for the CTV. Prerequisite for this calculation was the simplification of the complex prostate geometry to a sphere. No new treatment-planning procedure was necessary during external-beam radiotherapy.
  
  
  CONCLUSIONS
  HDR brachytherapy does change the prostate volume. Under the condition of a 10-mm safety margin in each direction added to the CTV for the PTV, no new treatment-planning procedure was necessary after HDR brachytherapy. There is no need for CT scans at regular intervals during external-beam radiotherapy.
authors.affiliation: Department of Radiotherapy and Radiooncology, University of Göttingen, Germany. markusherrmann@med.uni-goettingen.de
authors.forename: Markus Karl Alfred
authors.initials: MK
authors.lastname: Herrmann
authors.forename: Tammo
authors.initials: T
authors.lastname: Gsänger
authors.forename: Arne
authors.initials: A
authors.lastname: Strauss
authors.forename: Tereza
authors.initials: T
authors.lastname: Kertesz
authors.forename: Hendrik A
authors.initials: HA
authors.lastname: Wolff
authors.forename: Hans
authors.initials: H
authors.lastname: Christiansen
authors.forename: Hilke
authors.initials: H
authors.lastname: Vorwerk
authors.forename: Clemens Friedrich
authors.initials: CF
authors.lastname: Hess
authors.forename: Andrea
authors.initials: A
authors.lastname: Hille
mesh_terms: D000368:Aged; D006801:Humans; D008297:Male; D008875:Middle Aged; D009929:Organ Size; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D020266:Radiotherapy, Conformal / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000379:methods*; D016896:Treatment Outcome