title: A parametrization of the CT number of a substance and its use for stoichiometric calibration.
abstract: A method to carry out stoichiometric calibrations of CT scanners employed in radiotherapy treatment planning is proposed. The method is based on a simple parametrization of the CT number of a substance, which involves only two variables to describe the substance (electron density and one effective atomic number) and one parameter to describe the beam. The method was tested experimentally on a group of beams. A set of no tissue-like substances of known densities and elemental compositions were employed as calibrators. CT number-to-density curves (RED curves) were calculated with the proposed parametrization and compared to those measured with a commercial density phantom. Differences between the electron densities assigned by the calculated RED curves and the measured ones were in the range 0.009-0.019 (RMS). The proposed method may be employed to carry out accurate stoichiometric calibrations by using only one suitable substance as calibrator, not necessarily tissue-like.
authors.affiliation: Medical Physics and Radiation Protection Service, 12 de Octubre University Hospital, Madrid, Spain. lmartinezg.hdoc@salud.madrid.org
authors.forename: Luis C
authors.initials: LC
authors.lastname: Martinez
authors.forename: Alfonso
authors.initials: A
authors.lastname: Calzado
authors.forename: Cesar
authors.initials: C
authors.lastname: Rodriguez
authors.forename: Rosa
authors.initials: R
authors.lastname: Gilarranz
authors.forename: Maria J
authors.initials: MJ
authors.lastname: Manzanas
mesh_terms: D002138:Calibration; D016014:Linear Models; D017785:Photons; D011880:Radiotherapy Planning, Computer-Assisted; D014057:Tomography, X-Ray Computed / Q000592:standards*