Conversion of CT numbers into tissue parameters for Monte Carlo dose calculations: a multi-centre study.
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.
Vanderstraeten
Barbara
B
Department of Medical Physics, Ghent University, Gent, Belgium.
Chin
Pik Wai
PW
Velindre Cancer Centre, Department of Medical Physics, Cardiff, UK.
Fix
Michael
M
Division of Medical Radiation Physics, Inselspital-University of Berne, Berne, Switzerland.
Leal
Antonio
A
Department of Medical Physiology and Biophysics, University of Seville and Virgen Macarena Hospital, Seville, Spain.
Mora
Grisel
G
Nuclear Physics Centre, University of Lisbon, Lisbon, Portugal.
Reynaert
Nick
N
Department of Medical Physics, Ghent University, Gent, Belgium.
Seco
Joao
J
Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.
Soukup
Martin
M
Section for Biomedical Physics, University Hospital Tuebingen, Tuebingen, Germany.
Spezi
Emiliano
E
Servizio di Fisica Sanitaria, Policlinico S.Orsola Malpighi, Bologna, Italy.
De Neve
Wilfried
W
Department of Radiotherapy, Ghent University Hospital, Gent, Belgium.
Thierens
Hubert
H
Department of Medical Physics, Ghent University, Gent, Belgium.
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*