title: An experimental MOSFET approach to characterize (192)Ir HDR source anisotropy.
abstract: The dose anisotropy around a (192)Ir HDR source in a water phantom has been measured using MOSFETs as relative dosimeters. In addition, modeling using the EGSnrc code has been performed to provide a complete dose distribution consistent with the MOSFET measurements. Doses around the Nucletron 'classic' (192)Ir HDR source were measured for a range of radial distances from 5 to 30 mm within a 40 x 30 x 30 cm(3) water phantom, using a TN-RD-50 MOSFET dosimetry system with an active area of 0.2 mm by 0.2 mm. For each successive measurement a linear stepper capable of movement in intervals of 0.0125 mm re-positioned the MOSFET at the required radial distance, while a rotational stepper enabled angular displacement of the source at intervals of 0.9 degrees . The source-dosimeter arrangement within the water phantom was modeled using the standardized cylindrical geometry of the DOSRZnrc user code. In general, the measured relative anisotropy at each radial distance from 5 mm to 30 mm is in good agreement with the EGSnrc simulations, benchmark Monte Carlo simulation and TLD measurements where they exist. The experimental approach employing a MOSFET detection system of small size, high spatial resolution and fast read out capability allowed a practical approach to the determination of dose anisotropy around a HDR source.
authors.affiliation: Radiation Oncology Victoria, Melbourne, Australia. wtoye@radoncvic.com.au
authors.forename: W C
authors.initials: WC
authors.lastname: Toye
authors.forename: K R
authors.initials: KR
authors.lastname: Das
authors.forename: S P
authors.initials: SP
authors.lastname: Todd
authors.forename: M B
authors.initials: MB
authors.lastname: Kenny
authors.forename: R D
authors.initials: RD
authors.lastname: Franich
authors.forename: P N
authors.initials: PN
authors.lastname: Johnston
mesh_terms: D016880:Anisotropy; D001918:Brachytherapy / Q000379:methods*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D007496:Iridium Radioisotopes / Q000032:analysis* / Q000737:chemistry*; D011874:Radiometry / Q000295:instrumentation* / Q000379:methods; D011879:Radiotherapy Dosage; D015203:Reproducibility of Results; D012542:Scattering, Radiation; D012680:Sensitivity and Specificity; D014173:Transistors, Electronic
chemical_list: D007496:Iridium Radioisotopes