title: Investigation of interseed attenuation and tissue composition effects in (125)I seed implant prostate brachytherapy.
abstract: OBJECTIVE
  To use Monte Carlo (MC) simulation and sector analysis to assess interseed attenuation and scatter (ISA) and tissue effects in permanent seed implant prostate brachytherapy and to compare methods for modeling tissue.
  
  
  METHODS
  CT-based postimplant plan simulations for 40 patients were evaluated using dose-volume histogram (DVH) parameters and sector analysis. Simulations in water (to evaluate ISA alone) and tissue assigned from contours or CT data, with and without calcifications, were compared.
  
  
  RESULTS
  For patients without calcifications, mean combined ISA and tissue effect reduced prostate D90 by 4.2 Gy (2.9%), prostate V100 by 0.5 cm(3) (1.4%), urethra D10 by 8.6 Gy (3.5%), rectal [Formula: see text] by 11.6 Gy (10.5%), and the 100% isodose volume by 4.7 cm(3). Larger differences were observed comparing planned dose to postimplant, mean prostate D90 reduced from 185 to 149.8 Gy (-19%). For patients with calcifications, larger tissue effects were observed, prostate D90 reduced by up to 7.4%. Sector analysis showed dose reductions were larger in anterior and base sectors of the prostate. For patients without calcifications, contour- and CT-based tissue model results agreed within <0.5% for all DVH parameters, with up to 4% difference for patients with calcifications.
  
  
  CONCLUSIONS
  Advanced brachytherapy dose calculation methods that take account of ISA and tissue effects show that clinical (125)I implant dose is different from TG-43U1 (AAPM Task Group No. 43 Report-Update 1) calculations, reducing DVH parameter values particularly for patients with calcifications. Peripheral dose and areas of the implant with relatively poorer coverage are particularly affected. However, dose reductions are small compared with other postimplant dose uncertainties.
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: Clinical Oncology, St. James's Institute of Oncology, St. James's University Hospital, Leeds, UK.
authors.forename: Ann
authors.initials: A
authors.lastname: Henry
authors.affiliation: Academic Unit of Medical Physics, University of Leeds, Leeds, UK; Institute of Medical Physics, School of Physics, University of Sydney, NSW, Australia.
authors.forename: David
authors.initials: D
authors.lastname: Thwaites
mesh_terms: D000465:Algorithms; D001918:Brachytherapy / Q000295:instrumentation / Q000379:methods*; D002114:Calcinosis / Q000532:radiotherapy; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D008297:Male; D008954:Models, Biological; D009010:Monte Carlo Method; D011467:Prostate / Q000528:radiation effects*; D011471:Prostatic Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D012007:Rectum / Q000528:radiation effects; D014521:Urethra / Q000528:radiation effects
chemical_list: D007457:Iodine Radioisotopes
keywords: Inter seed attenuation; Monte Carlo simulation; Prostate brachytherapy; Tissue composition