title: Anisotropy functions for 169Yb brachytherapy seed models 5, 8 and X1267. An EGS4 Monte Carlo study.
abstract: Anisotropy functions for 169Yb sources used in interstitial brachytherapy are investigated. A comprehensive study of several factors affecting the angular dose distribution around four 169Yb seed models (Amersham International) has been undertaken. Absolute dose rates around 169Yb seed models 5, 8a, 8b and X1267 have been estimated by means of the EGS4 Monte Carlo Simulation System. An updated cross section library (DLC-136/PHOTX), binding corrections for Compton scattering and water molecular form factors were included in the calculations. Following the formalism developed by the Interstitial Brachytherapy Collaborative Working Group, anisotropy functions, F(r, theta), have been calculated and compared with other Monte Carlo results and whenever possible with experimental data. Excellent agreement is found with other Monte Carlo calculations. Considering the large experimental errors reported, a fairly good coincidence has been achieved between experimental and Monte Carlo data for models 8a and 8b. For model X1267 large discrepancies with experiment are obtained. Monte Carlo calculations for all seed models showed model 5 to be the least anisotropic and models 8b and X1267 to be almost identical. Statistical fluctuations can be drastically reduced computationally, offering an efficient alternative to measured data. Our results have estimated uncertainties of 0.5%-1.0% within one standard deviation everywhere excluding the longitudinal source axis, where uncertainties are below 3% up to 5 cm, this accuracy being excellent for clinical calculations.
authors.affiliation: Departamento de Física, Centro de Estudios Aplicados al Desarrollo Nuclear, Miramar, La Habana, Cuba. mainegra@ceaden.edu.cu
authors.forename: E
authors.initials: E
authors.lastname: Mainegra
authors.forename: R
authors.initials: R
authors.lastname: Capote
authors.forename: E
authors.initials: E
authors.lastname: López
mesh_terms: D016880:Anisotropy; D001918:Brachytherapy / Q000295:instrumentation* / Q000379:methods*; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011868:Radioisotopes / Q000627:therapeutic use*; D011874:Radiometry; D012542:Scattering, Radiation; D014867:Water; D015018:Ytterbium / Q000627:therapeutic use*
chemical_list: D011868:Radioisotopes; D014867:Water; D015018:Ytterbium