title: Properties of liquid ionization chambers at LDR brachytherapy dose rates.
abstract: Properties such as sensitivity, general recombination and reproducibility of liquid-filled parallel-plate ionization chambers for dosimetry in low-dose-rate brachytherapy radiation fields have been evaluated. Two different dielectric liquids, isooctane (C8H(1)8) and tetramethylsilane (Si(CH3)4), have been used as sensitive media in chambers having a coin-shaped sensitive volume of 3 mm in diameter and 1 mm thickness. An electric field strength of 300 kV m-1 was found to be optimal with respect to sensitivity, leakage current and general recombination. At absorbed dose rates from 0.1-100 mGy min-1 the ionization charge measurements at an irradiation time of 1 min showed a reproducibility better than 1%, and a general recombination not exceeding 0.5%. The calibration--absorbed dose to water against ionization charge at a 60Co reference source--did not show any significant change over an observation time of one year for any of the chambers.
authors.affiliation: Radiation Physics Department, Umeå University, Sweden.
authors.forename: B
authors.initials: B
authors.lastname: Johansson
authors.forename: G
authors.initials: G
authors.lastname: Wickman
authors.forename: T
authors.initials: T
authors.lastname: Holmström
mesh_terms: D001918:Brachytherapy / Q000295:instrumentation* / Q000379:methods; D006207:Half-Life; D006801:Humans; D009795:Octanes; D011829:Radiation Dosage; D012821:Silanes; D013667:Technetium; D014297:Trimethylsilyl Compounds
chemical_list: D009795:Octanes; D012821:Silanes; D014297:Trimethylsilyl Compounds; C073196:tetramethylsilane; D013667:Technetium; C045798:2,2,4-trimethylpentane