title: Comparison of bulk electron density and voxel-based electron density treatment planning.
abstract: The use of magnetic resonance imaging (MRI) alone for radiation planning is limited by the lack of electron density for dose calculations. The purpose of this work is to evaluate the dosimetric accuracy of using bulk electron density as a substitute for computed tomography (CT)-derived electron density in intensity-modulated radiation therapy (IMRT) treatment planning of head and neck (HN) cancers. Ten clinically-approved, CT-based IMRT treatment plans of HN cancer were used for this study. Three dose distributions were calculated and compared for each treatment plan. The first calculation used CT-derived density and was assumed to be the most accurate. The second calculation used a homogeneous patient density of 1 g/cm3. For the third dose calculation, bone and air cavities were contoured and assigned a uniform density of 1.5 g/cm3 and 0 g/cm3, respectively. The remaining tissues were assigned a density of 1 g/cm3. The use of homogeneous anatomy resulted in up to 4%-5% deviations in dose distribution as compared to CT-derived electron density calculations. Assigning bulk density to bone and air cavities significantly improved the accuracy of the dose calculations. All parameters used to describe planning target volume coverage were within 2% of calculations based on CT-derived density. For organs at risk, most of the parameters were within 2%, with the few exceptions located in low-dose regions. The data presented here show that if bone and air cavities are overridden with the proper density, it is feasible to use a bulk electron density approach for accurate dose calculation in IMRT treatment planning of HN cancers. This may overcome the problem of the lack of electron density information should MRI-only simulation be performed.
authors.affiliation: Department of Medical Physics, Sunnybrook Health Sciences Center, Toronto, ON, Canada. alex.karotki@sunnybrook.ca
authors.forename: Aliaksandr
authors.initials: A
authors.lastname: Karotki
authors.forename: Katherine
authors.initials: K
authors.lastname: Mah
authors.forename: Gert
authors.initials: G
authors.lastname: Meijer
authors.forename: Michael
authors.initials: M
authors.lastname: Meltsner
mesh_terms: D004583:Electrons; D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*
references.citation: Radiother Oncol. 1997 Jan;42(1):1-15
references.pmid: 9132820
references.citation: Phys Med Biol. 2005 Apr 7;50(7):1343-61
references.pmid: 15798328
references.citation: J Appl Clin Med Phys. 2010 Jan 28;11(1):2961
references.pmid: 20160688
references.citation: Int J Radiat Oncol Biol Phys. 2004 Oct 1;60(2):636-47
references.pmid: 15380601
references.citation: Cancer Imaging. 2006 Jun 22;6:100-6
references.pmid: 16829471
references.citation: Radiother Oncol. 2008 Apr;87(1):100-9
references.pmid: 18262669
references.citation: Semin Radiat Oncol. 2005 Jul;15(3):136-45
references.pmid: 15983939
references.citation: Int J Radiat Oncol Biol Phys. 2001 Jul 1;50(3):821-7
references.pmid: 11395252
references.citation: Phys Med Biol. 1999 Nov;44(11):R99-155
references.pmid: 10588277
references.citation: Int J Radiat Oncol Biol Phys. 2007 Jul 1;68(3):903-11
references.pmid: 17544002
references.citation: Int J Radiat Oncol Biol Phys. 2009 Jun 1;74(2):644-51
references.pmid: 19427564
references.citation: Br J Radiol. 1998 May;71(845):544-8
references.pmid: 9691900
references.citation: Jpn J Clin Oncol. 2007 Jun;37(6):405-11
references.pmid: 17635965
references.citation: Radiother Oncol. 2003 Feb;66(2):203-16
references.pmid: 12648793
references.citation: Radiat Oncol. 2010 Jun 30;5:62
references.pmid: 20591179