title: Thick phosphor screens for on-line portal imaging.
abstract: Gd2O2S phosphor screens between 250 and 1000 mg/cm2 thick were evaluated for use in megavoltage imaging systems. The phosphor layers were placed on brass plates ranging from 1 to 5 mm thick, each with and without an optical back reflector (white paint). Light output and spatial resolution were measured at 6- and 23-MV x-ray energies. Light output was found to increase linearly with phosphor thickness up to 500 mg/cm2, reaching a plateau at 1000 mg/cm2. Spatial resolution [modulation transfer function (MTF)] decreased exponentially with phosphor thickness up to 750 mg/cm2, where a minimum was reached. The variation of MTF with phosphor thickness was found to obey a simple empirical relation.
authors.affiliation: Manitoba Cancer Treatment and Research Foundation, Winnipeg, Canada.
authors.forename: B
authors.initials: B
authors.lastname: Wowk
authors.forename: S
authors.initials: S
authors.lastname: Shalev
mesh_terms: D005682:Gadolinium; D006801:Humans; D008433:Mathematics; D008962:Models, Theoretical; D009862:Online Systems; D011859:Radiography / Q000295:instrumentation / Q000379:methods*; D014584:User-Computer Interface
chemical_list: C021197:gadolinium sulfoxylate; D005682:Gadolinium