title: Comparison of dose distributions around the pulsed-dose-rate Fletcher-Williamson and the low-dose-rate Fletcher-Suit-Delclos ovoids: a Monte Carlo study.
abstract: We performed a Monte Carlo study to compare dose distributions for a Fletcher-Suit-Delclos (FSD) ovoid used with (137)Cs low-dose-rate (LDR) sources with those for a Fletcher-Williamson (FW) ovoid used with an (192)Ir pulsed-dose-rate (PDR) source for intracavitary brachytherapy of cervical cancer. We recently reported on extensive validation of Monte Carlo MCNPX models of these ovoids using radiochromic film measurements. Here, we compared these models assuming identical loading of 10, 15 and 20 mgRaEq (72, 108 and 145 cGy cm(2) h(-1), respectively) in three dose mesh planes: one perpendicular to the ovoid long axis bisecting the ovoid, one parallel to and displaced 2 cm medially from the long axis of the ovoid, and a 'rectal' plane perpendicular to the long axis located 1 cm distal to the distal face of the ovoid cap. The FW ovoid delivered slightly higher doses (within 10%) over all loadings to regions away from the bladder and rectal shields when compared to the FSD ovoid. However, the FW ovoid delivered much higher doses (>50%) in regions near these shields. In the rectal plane, the FW ovoid delivered a slightly higher dose, but within the region directly behind the rectal shield, the FW ovoid delivered a dose ranging from +35% to -35% of the FSD dose distribution. We attribute these differences to intrinsic differences in source characteristics (radial dose function and anisotropy factors) and extrinsic factors such as the solid-angle effect between sources and shields and applicator design.
authors.affiliation: Department of Radiation Physics, Unit 1210, The University of Texas M D Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, Texas 77030, USA.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Price
authors.forename: Kent A
authors.initials: KA
authors.lastname: Gifford
authors.forename: John
authors.initials: J
authors.lastname: Horton
authors.forename: Ann
authors.initials: A
authors.lastname: Lawyer
authors.forename: Patricia
authors.initials: P
authors.lastname: Eifel
authors.forename: Firas
authors.initials: F
authors.lastname: Mourtada
mesh_terms: D001822:Body Burden; D001918:Brachytherapy / Q000295:instrumentation* / Q000379:methods*; D003198:Computer Simulation; D004307:Dose-Response Relationship, Radiation; D004867:Equipment Design; D019544:Equipment Failure Analysis; D006801:Humans; D008954:Models, Biological; D015233:Models, Statistical; D009010:Monte Carlo Method; D011874:Radiometry / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012062:Relative Biological Effectiveness; D012542:Scattering, Radiation