title: Dose perturbation due to the polysulfone cap surrounding a Fletcher-Williamson colpostat.
abstract: We conducted a metrological evaluation of the dosimetric impact due to the polysulfone cap used with the Fletcher-Williamson (FW) colpostat for 192Ir high-dose rate and pulsed-dose rate intracavitary brachytherapy using Monte Carlo simulations. Polysulfone caps with diameter of 30 mm, 25 mm, 20 mm, and 16 mm (mini-ovoid) were simulated and the absorbed dose rate in the surrounding water was calculated and compared to the dose rate for a bare 192Ir source in water. The dose perturbation depended on the cap diameter, distance away from the cap surface, and angular position around the cap. The largest dose rate reductions were found to be in the direction of the tumor bed where the cap is thickest. The range of perturbation over all depths and cap diameters was +2.8% (dose enhancement) to -6.8% (dose reduction). The FW colpostat cap's material composition should be modified to reduce this dosimetric effect or brachytherapy treatment planning dose algorithms should be improved to account for this perturbation.
authors.affiliation: Department of Medical Physics, Mary Bird Perkins Cancer Center, Louisiana State University Baton Rouge, LA, USA.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Price
authors.forename: Stephen F
authors.initials: SF
authors.lastname: Kry
authors.forename: Patricia J
authors.initials: PJ
authors.lastname: Eifel
authors.forename: Mohammad
authors.initials: M
authors.lastname: Salehpour
authors.forename: Firas
authors.initials: F
authors.lastname: Mourtada
mesh_terms: D000465:Algorithms; D001918:Brachytherapy / Q000295:instrumentation*; D005260:Female; D006801:Humans; D007496:Iridium Radioisotopes / Q000627:therapeutic use*; D009010:Monte Carlo Method; D009092:Mucous Membrane / Q000528:radiation effects; D011108:Polymers / Q000737:chemistry*; D011482:Protective Devices; D011874:Radiometry; D011879:Radiotherapy Dosage; D012007:Rectum; D012062:Relative Biological Effectiveness; D013450:Sulfones / Q000737:chemistry*; D014414:Tungsten / Q000737:chemistry; D001743:Urinary Bladder; D002583:Uterine Cervical Neoplasms / Q000532:radiotherapy*; D014621:Vagina / Q000528:radiation effects
chemical_list: D007496:Iridium Radioisotopes; D011108:Polymers; D013450:Sulfones; C017662:polysulfone P 1700; D014414:Tungsten