title: Monte Carlo calculations of output factors for clinically shaped electron fields.
abstract: We report on the use of the EGS4/BEAM Monte Carlo technique to predict the output factors for clinically relevant, irregularly shaped inserts as they intercept a linear accelerator's electron beams. The output factor for a particular combination--energy, cone, insert, and source-to-surface distance (SSD)--is defined in accordance with AAPM TG-25 as the product of cone correction factor and insert correction factor, evaluated at the depth of maximum dose. Since cone correction factors are easily obtained, we focus our investigation on the insert correction factors (ICFs). An analysis of the inserts used in routine clinical practice resulted in the identification of a set of seven "idealized" shapes characterized by specific parameters. The ICFs for these shapes were calculated using a Monte Carlo method (EGS4/BEAM) and measured for a subset of them using an ion chamber and well-established measurement methods. Analytical models were developed to predict the Monte Carlo-calculated ICF values for various electron energies, cone sizes, shapes, and SSDs. The goodness-of-fit between predicted and Monte Carlo-calculated ICF values was tested using the Kolmogorov-Smirnoff statistical test. Results show that Monte Carlo-calculated ICFs match the measured values within 2.0% for most of the shapes considered, except for few highly elongated fields, where deviations up to 4.0% were recorded. Predicted values based on analytical modeling agree with measured ICF values within 2% to 3% for all configurations. We conclude that the predicted ICF values based on modeling of Monte Carlo-calculated values could be introduced in clinical use.
authors.affiliation: Department of Radiation Oncology, University of Illinois Medical Center, OCC C-400, 1801 W. Taylor Street, Chicago, Illinois 60612, USA. turian@uic.edu
authors.forename: Julius V
authors.initials: JV
authors.lastname: Turian
authors.forename: Brett D
authors.initials: BD
authors.lastname: Smith
authors.forename: Damian A
authors.initials: DA
authors.lastname: Bernard
authors.forename: Katherine L
authors.initials: KL
authors.lastname: Griem
authors.forename: James C
authors.initials: JC
authors.lastname: Chu
mesh_terms: D001822:Body Burden; D003198:Computer Simulation; D004583:Electrons / Q000627:therapeutic use*; D006801:Humans; D008954:Models, Biological; D015233:Models, Statistical; D009010:Monte Carlo Method; D010315:Particle Accelerators; D011874:Radiometry / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012062:Relative Biological Effectiveness; D012542:Scattering, Radiation
references.citation: Med Phys. 1991 Jan-Feb;18(1):73-109
references.pmid: 1901132
references.citation: Med Phys. 1989 Jan-Feb;16(1):88-93
references.pmid: 2921987
references.citation: Med Phys. 1993 Sep-Oct;20(5):1417-27
references.pmid: 8289724
references.citation: Med Phys. 2001 Aug;28(8):1735-45
references.pmid: 11548944
references.citation: Phys Med Biol. 1998 Dec;43(12):3479-94
references.pmid: 9869026
references.citation: Med Phys. 1994 Apr;21(4):559-66
references.pmid: 8058023
references.citation: Med Phys. 2001 Jun;28(6):938-49
references.pmid: 11439490
references.citation: Med Phys. 1982 Jan-Feb;9(1):60-8
references.pmid: 6804772
references.citation: Med Phys. 1994 Aug;21(8):1251-60
references.pmid: 7799867
references.citation: Med Phys. 1995 May;22(5):503-24
references.pmid: 7643786
references.citation: Med Phys. 1983 May-Jun;10(3):356-60
references.pmid: 6877183
references.citation: Med Phys. 1998 Sep;25(9):1711-6
references.pmid: 9775377
references.citation: Phys Med Biol. 1998 Oct;43(10):2741-54
references.pmid: 9814514
references.citation: Int J Radiat Oncol Biol Phys. 1979 Mar;5(3):433-40
references.pmid: 110749
references.citation: Med Phys. 1983 Nov-Dec;10(6):741-71
references.pmid: 6419029
references.citation: Med Phys. 1999 May;26(5):743-50
references.pmid: 10360536
references.citation: Radiother Oncol. 1988 Apr;11(4):395-404
references.pmid: 3131845
references.citation: Phys Med Biol. 1999 Dec;44(12):R157-89
references.pmid: 10616140
references.citation: Med Phys. 1998 May;25(5):656-61
references.pmid: 9608475
references.citation: Med Phys. 2002 May;29(5):771-86
references.pmid: 12033573