title: Dosimetry modeling for focal high-dose-rate prostate brachytherapy.
abstract: OBJECTIVE
  The dosimetry of focal high-dose-rate prostate brachytherapy was assessed. Dose volume histogram parameters, robustness to source position errors, and Monte Carlo (MC) simulations were compared for whole-gland (WG), hemi-gland (HEMI), and ultra-focal (UF) treatment plans.
  
  
  METHODS
  Tumor volumes were delineated based on MRI and template biopsy results for 9 patients. WG, HEMI, and UF plans were produced assuming 19 Gy single fraction monotherapy treatments. For UF plans, a 6-mm margin was applied to the visible tumor to create a focal-planning target volume (F-PTV). Systematic source position shifts of 1-4 mm were applied to assess plan robustness. The dosimetric impact of steel catheters was assessed using MC simulation.
  
  
  RESULTS
  Mean D90 and V100 were 20.4 Gy and 97.9% for prostate in WG plans, 22.2 Gy and 98.1% for hemi-prostate in HEMI plans, and 23.0 Gy and 98.2% for F-PTV in UF plans. Mean urethra D10 was 20.3, 19.7, and 9.2 Gy in WG, HEMI, and UF plans, respectively. Mean rectal D2cc was 12.5, 9.8, and 4.6 Gy in WG, HEMI, and UF plans, respectively. Focal treatment plans were sensitive to source position errors-2 mm systematic shifts reduced mean prostate D90 by 0.7%, hemi-prostate D90 by 2.6%, and F-PTV D90 by 8.3% in WG, HEMI, and UF plans, respectively. MC simulation results were similar for all plan types with most dose volume histogram parameters reduced by <2%.
  
  
  CONCLUSIONS
  HEMI and UF treatments can achieve higher D90 values compared with WG treatments with reduced organ at risk dose. Focal treatments are more sensitive to systematic source position errors than WG treatments.
authors.affiliation: Department of Medical Physics and Engineering, St. James's Institute of Oncology, St. James's University Hospital, Leeds, UK; Academic Unit of Medical Physics, University of Leeds, Leeds, UK. Electronic address: Joshua.Mason@leedsth.nhs.uk.
authors.forename: Josh
authors.initials: J
authors.lastname: Mason
authors.affiliation: Department of Medical Physics and Engineering, St. James's Institute of Oncology, St. James's University Hospital, Leeds, UK.
authors.forename: Bashar
authors.initials: B
authors.lastname: Al-Qaisieh
authors.affiliation: Department of Medical Physics and Engineering, St. James's Institute of Oncology, St. James's University Hospital, Leeds, UK.
authors.forename: Peter
authors.initials: P
authors.lastname: Bownes
authors.affiliation: Academic Unit of Medical Physics, University of Leeds, Leeds, UK; Institute of Medical Physics, School of Physics, University of Sydney, Sydney, New South Wales, Australia.
authors.forename: David
authors.initials: D
authors.lastname: Thwaites
authors.affiliation: Clinical Oncology, St. James's Institute of Oncology, St. James's University Hospital, Leeds, UK.
authors.forename: Ann
authors.initials: A
authors.lastname: Henry
mesh_terms: D000368:Aged; D001918:Brachytherapy / Q000379:methods*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009010:Monte Carlo Method; D058958:Organs at Risk / Q000528:radiation effects; D011471:Prostatic Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D011874:Radiometry / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D047368:Tumor Burden; D014521:Urethra / Q000528:radiation effects
keywords: Focal therapy; High-dose-rate brachytherapy; Prostate brachytherapy