title: Relative electron density calibration of CT scanners for radiotherapy treatment planning.
abstract: Several authors have reported data on the variation of Hounsfield numbers with electron density in CT scanners. The data can be fitted with a double straight line approach. For non-bone tissues (or phantom materials with similar atomic numbers) the data from all authors can be fitted to a single straight line. For bone-like materials the line varies between authors. The method used to measure electron density has a greater effect than the differences between scanners, or the kilovoltage used on a given scanner. The effect of variation of these slopes on the accuracy of radiotherapy treatment planning is analysed. For typical radiotherapy beams, to produce a 1% error in dosimetry would require errors of over 8% in bone electron density. Using a single pair of calibration lines for all the scanners reported would give dosimetric errors of under 0.8%. A formula is recommended as a default for use in planning systems in circumstances where no data are available for a particular scanner.
authors.affiliation: Medical Physics Department, Addenbrooke's Hospital, Cambridge, UK.
authors.forename: S J
authors.initials: SJ
authors.lastname: Thomas
mesh_terms: D002138:Calibration; D004583:Electrons; D006801:Humans; D011880:Radiotherapy Planning, Computer-Assisted; D015898:Tomography Scanners, X-Ray Computed