title: Evaluation of the eclipse electron Monte Carlo dose calculation for small fields.
abstract: Varian Medical Systems (Palo Alto, CA) has implemented the Monte Carlo electron dose calculation algorithm (eMC) in the Eclipse treatment planning system. Previous algorithms for electron treatment planning were limited in their calculation ability for small field depth doses and monitor units. An old rule of thumb to approximate the limiting cutout size for an electron field was determined by the lateral scatter equilibrium and approximated by E (MeV)/2.5 in centimeters of water. In this study we compared eMC calculations and measurements of depth doses, isodose distributions and monitor units for several different energy and small field cutout size combinations at different SSDs. Measurements were made using EBT film (International Specialty Products, Wayne, NJ) and a PinPoint Ion Chamber (PTW, Hicksville, NY). Our results indicate that the eMC algorithm can accurately predict depth doses, isodose distributions and monitor units (within 2.5%) for field sizes as small as 3.0 cm diameter for energies in the 6 to 20 MeV range at 100 cm SSD. Therefore, the previous energy dependent rule of thumb does not apply to the Eclipse electron Monte Carlo code. However, at extended SSDs (105-110 cm), the results show good agreement (within 4 %) only for higher energies (12, 16, and 20 MeV) for a field size of 3 cm.
authors.affiliation: Department of Radiation Oncology, Stony Brook University Medical Center, Stony Brook, New York.
authors.forename: Zhigang
authors.initials: Z
authors.lastname: Xu
authors.affiliation: Department of Radiation Oncology, Stony Brook University Medical Center, Stony Brook, New York.
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Walsh
authors.affiliation: Department of Radiation Oncology, Stony Brook University Medical Center, Stony Brook, New York.
authors.forename: Tejas P
authors.initials: TP
authors.lastname: Telivala
authors.affiliation: Department of Radiation Oncology, Stony Brook University Medical Center, Stony Brook, New York.
authors.forename: Allen G
authors.initials: AG
authors.lastname: Meek
authors.affiliation: Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, Commack, New York.
authors.forename: Guozhen
authors.initials: G
authors.lastname: Yang
mesh_terms: D000465:Algorithms; D004583:Electrons; D009010:Monte Carlo Method; D011880:Radiotherapy Planning, Computer-Assisted
references.citation: Acta Radiol Oncol. 1980;19(3):199-207
references.pmid: 6257038
references.citation: Med Phys. 2007 Jun;34(6):1967-74
references.pmid: 17654899
references.citation: Med Phys. 2005 Jul;32(7):2245-53
references.pmid: 16121579
references.citation: Med Phys. 2006 May;33(5):1321-8
references.pmid: 16752567
references.citation: Med Phys. 1998 May;25(5):656-61
references.pmid: 9608475
references.citation: Med Phys. 1998 Jul;25(7 Pt 1):1217-21
references.pmid: 9682209
references.citation: Med Phys. 2006 Jun;33(6):1540-51
references.pmid: 16872061
references.citation: Phys Med Biol. 2006 Jun 7;51(11):2781-99
references.pmid: 16723766
references.citation: Phys Med Biol. 1995 Apr;40(4):543-74
references.pmid: 7610114
references.citation: Med Phys. 2006 Nov;33(11):4064-72
references.pmid: 17153386
references.citation: Med Phys. 2003 Sep;30(9):2455-64
references.pmid: 14528967