title: Computed tomography as a source of electron density information for radiation treatment planning.
abstract: OBJECTIVE
  To evaluate the performance of computed tomography (CT) systems of various designs as a source of electron density (rho(el)) data for treatment planning of radiation therapy.
  
  
  METHODS
  Dependence of CT numbers on relative electron density of tissue-equivalent materials (HU-rho(el) relationship) was measured for several general-purpose CT systems (single-slice, multislice, wide-bore multislice), for radiotherapy simulators with a single-slice CT and kV CBCT (cone-beam CT) options, as well as for linear accelerators with kV and MV CBCT systems. Electron density phantoms of four sizes were used. Measurement data were compared with the standard HU-rhoel relationships predefined in two commercial treatment-planning systems (TPS).
  
  
  RESULTS
  The HU-rho(el) relationships obtained with all of the general-purpose CT scanners operating at voltages close to 120 kV were very similar to each other and close to those predefined in TPS. Some dependency of HU values on tube voltage was observed for bone- equivalent materials. For a given tube voltage, differences in results obtained for different phantoms were larger than those obtained for different CT scanners. For radiotherapy simulators and for kV CBCT systems, the information on rhoel was much less precise because of poor uniformity of images. For MV CBCT, the results were significantly different than for kV systems due to the differing energy spectrum of the beam.
  
  
  CONCLUSIONS
  The HU-rho(el) relationships predefined in TPS can be used for general-purpose CT systems operating at voltages close to 120 kV. For nontypical imaging systems (e.g., CBCT), the relationship can be significantly different and, therefore, it should always be measured and carefully analyzed before using CT data for treatment planning.
authors.affiliation: Medical Physics Department, Center of Oncology, Warsaw, Poland. w.skrzynski@zfm.coi.pl
authors.forename: Witold
authors.initials: W
authors.lastname: Skrzyński
authors.forename: Sylwia
authors.initials: S
authors.lastname: Zielińska-Dabrowska
authors.forename: Marta
authors.initials: M
authors.lastname: Wachowicz
authors.forename: Wioletta
authors.initials: W
authors.lastname: Slusarczyk-Kacprzyk
authors.forename: Paweł F
authors.initials: PF
authors.lastname: Kukołowicz
authors.forename: Wojciech
authors.initials: W
authors.lastname: Bulski
mesh_terms: D054893:Cone-Beam Computed Tomography / Q000295:instrumentation / Q000379:methods*; D004583:Electrons; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000295:instrumentation* / Q000379:methods*; D010315:Particle Accelerators; D019047:Phantoms, Imaging; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000295:instrumentation / Q000379:methods*
references.citation: Phys Med Biol. 2002 Sep 7;47(17):N223-31
references.pmid: 12361225
references.citation: Strahlenther Onkol. 2008 Jan;184(1):8-14
references.pmid: 18188517
references.citation: Phys Med Biol. 2002 May 7;47(9):1485-92
references.pmid: 12043814
references.citation: Phys Med Biol. 1979 Jul;24(4):802-9
references.pmid: 472014
references.citation: Int J Radiat Oncol Biol Phys. 2007 Mar 15;67(4):1201-10
references.pmid: 17336221
references.citation: Int J Radiat Oncol Biol Phys. 2006 Dec 1;66(5):1553-61
references.pmid: 17056197
references.citation: Med Phys. 2001 Feb;28(2):220-31
references.pmid: 11243347
references.citation: Med Phys. 2009 Apr;36(4):1421-32
references.pmid: 19472649
references.citation: Strahlenther Onkol. 2009 May;185(5):318-24
references.pmid: 19440671
references.citation: Strahlenther Onkol. 2009 Dec;185(12):799-807
references.pmid: 20013089
references.citation: Strahlenther Onkol. 2008 Feb;184(2):100-4
references.pmid: 18259702
references.citation: Radiother Oncol. 1998 Sep;48(3):335-8
references.pmid: 9925254
references.citation: Br J Radiol. 1999 Aug;72(860):781-6
references.pmid: 10624344
references.citation: Med Phys. 1992 Mar-Apr;19(2):325-7
references.pmid: 1584125
references.citation: Med Phys. 2006 Feb;33(2):540-52
references.pmid: 16532961
references.citation: Radiother Oncol. 1986 Apr;5(4):337-45
references.pmid: 3726171
references.citation: Phys Med Biol. 2009 Apr 7;54(7):2067-77
references.pmid: 19287087
references.citation: Strahlenther Onkol. 2008 May;184(5):256-61
references.pmid: 18427756
references.citation: J Appl Clin Med Phys. 2006 Nov 28;7(4):1-12
references.pmid: 17533351
references.citation: Strahlenther Onkol. 2008 Nov;184(11):586-91
references.pmid: 19016017