title: Conversion of CT numbers into tissue parameters for Monte Carlo dose calculations: a multi-centre study.
abstract: The conversion of computed tomography (CT) numbers into material composition and mass density data influences the accuracy of patient dose calculations in Monte Carlo treatment planning (MCTP). The aim of our work was to develop a CT conversion scheme by performing a stoichiometric CT calibration. Fourteen dosimetrically equivalent tissue subsets (bins), of which ten bone bins, were created. After validating the proposed CT conversion scheme on phantoms, it was compared to a conventional five bin scheme with only one bone bin. This resulted in dose distributions D(14) and D(5) for nine clinical patient cases in a European multi-centre study. The observed local relative differences in dose to medium were mostly smaller than 5%. The dose-volume histograms of both targets and organs at risk were comparable, although within bony structures D(14) was found to be slightly but systematically higher than D(5). Converting dose to medium to dose to water (D(14) to D(14wat) and D(5) to D(5wat)) resulted in larger local differences as D(5wat) became up to 10% higher than D(14wat). In conclusion, multiple bone bins need to be introduced when Monte Carlo (MC) calculations of patient dose distributions are converted to dose to water.
authors.affiliation: Department of Medical Physics, Ghent University, Gent, Belgium.
authors.forename: Barbara
authors.initials: B
authors.lastname: Vanderstraeten
authors.affiliation: Velindre Cancer Centre, Department of Medical Physics, Cardiff, UK.
authors.forename: Pik Wai
authors.initials: PW
authors.lastname: Chin
authors.affiliation: Division of Medical Radiation Physics, Inselspital-University of Berne, Berne, Switzerland.
authors.forename: Michael
authors.initials: M
authors.lastname: Fix
authors.affiliation: Department of Medical Physiology and Biophysics, University of Seville and Virgen Macarena Hospital, Seville, Spain.
authors.forename: Antonio
authors.initials: A
authors.lastname: Leal
authors.affiliation: Nuclear Physics Centre, University of Lisbon, Lisbon, Portugal.
authors.forename: Grisel
authors.initials: G
authors.lastname: Mora
authors.affiliation: Department of Medical Physics, Ghent University, Gent, Belgium.
authors.forename: Nick
authors.initials: N
authors.lastname: Reynaert
authors.affiliation: Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.
authors.forename: Joao
authors.initials: J
authors.lastname: Seco
authors.affiliation: Section for Biomedical Physics, University Hospital Tuebingen, Tuebingen, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Soukup
authors.affiliation: Servizio di Fisica Sanitaria, Policlinico S.Orsola Malpighi, Bologna, Italy.
authors.forename: Emiliano
authors.initials: E
authors.lastname: Spezi
authors.affiliation: Department of Radiotherapy, Ghent University Hospital, Gent, Belgium.
authors.forename: Wilfried
authors.initials: W
authors.lastname: De Neve
authors.affiliation: Department of Medical Physics, Ghent University, Gent, Belgium.
authors.forename: Hubert
authors.initials: H
authors.lastname: Thierens
mesh_terms: D055592:Biophysical Phenomena; D001703:Biophysics; D005260:Female; D006801:Humans; D008297:Male; D009010:Monte Carlo Method; D009369:Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D019047:Phantoms, Imaging; D011880:Radiotherapy Planning, Computer-Assisted / Q000706:statistics & numerical data*; D011882:Radiotherapy, High-Energy; D014057:Tomography, X-Ray Computed / Q000706:statistics & numerical data*