title: Parallel-plate ionization chamber response in cobalt-60 irradiated transition zones.
abstract: The authors study the acceptance of a Capintec parallel-plate ionization chamber. The Capintec chamber is used for dose measurements in a lead and polystyrene slab phantom irradiated with cobalt-60 gamma rays. The authors define an enhancement ratio to quantify the dose measurements. The enhancement ratio equals the ratio of dose measured with the lead slab present to dose measured under equilibrium conditions in polystyrene at equal primary beam attenuation. The measured enhancement ratio at the exit side of the lead/polystyrene interface is 25% lower than the Monte Carlo predicted enhancement ratio. The authors propose that geometric acceptance limitations of the Capintec chamber to large-angle, low-energy electrons are the cause for this difference. A Monte Carlo simulation of the Capintec chamber acceptance confirms the hypothesis.
authors.affiliation: University of Rochester Cancer Center, Department of Radiation Oncology, New York 14642.
authors.forename: H M
authors.initials: HM
authors.lastname: Kooy
authors.forename: L D
authors.initials: LD
authors.lastname: Simpson
authors.forename: J A
authors.initials: JA
authors.lastname: McFaul
mesh_terms: D003037:Cobalt Radioisotopes / Q000627:therapeutic use*; D005720:Gamma Rays; D006801:Humans; D008953:Models, Anatomic; D011878:Radiotherapy / Q000295:instrumentation*; D011879:Radiotherapy Dosage; D013679:Technology, Radiologic
chemical_list: D003037:Cobalt Radioisotopes