title: First tests of a liquid ionization chamber to monitor intensity modulated radiation beams.
abstract: First measurements with a prototype ionization chamber are described to be applied in online monitoring of modulated fields in radiation therapy. The liquids isooctane, isononane (TMP) and tetramethylsilane (TMS) are used in a high purity grade in order to realize high current signals for electronic read-out in parallel at frequencies exceeding 10 Hz. Signals of more than a factor 4 with respect to isooctane, analysis grade, are obtained. With an electrode structure of 400 pads, a uniformity in efficiency within 1.2% has been measured. The penumbra of a multileaf collimator could be resolved. Theoretical examination verifies that the free electrons in the liquids cause higher signals when the measured currents are compared with expectation for ion transport only.
authors.affiliation: University of Karlsruhe, Institut für Experimentelle Kernphysik, PO Box 3640, 76021 Karlsruhe, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Eberle
authors.forename: J
authors.initials: J
authors.lastname: Engler
authors.forename: G
authors.initials: G
authors.lastname: Hartmann
authors.forename: R
authors.initials: R
authors.lastname: Hofmann
authors.forename: J R
authors.initials: JR
authors.lastname: Hörandel
mesh_terms: D003198:Computer Simulation; D004867:Equipment Design; D019544:Equipment Failure Analysis / Q000379:methods*; D005240:Feasibility Studies; D008962:Models, Theoretical; D009795:Octanes / Q000528:radiation effects*; D009862:Online Systems / Q000295:instrumentation; D010420:Pentanes / Q000528:radiation effects*; D010865:Pilot Projects; D011835:Radiation Protection / Q000295:instrumentation* / Q000379:methods; D011874:Radiometry / Q000295:instrumentation* / Q000379:methods; D011879:Radiotherapy Dosage; D020266:Radiotherapy, Conformal / Q000295:instrumentation* / Q000379:methods; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012821:Silanes / Q000528:radiation effects*; D012996:Solutions / Q000528:radiation effects; D014159:Transducers; D014297:Trimethylsilyl Compounds
chemical_list: D009795:Octanes; D010420:Pentanes; D012821:Silanes; D012996:Solutions; D014297:Trimethylsilyl Compounds; C073196:tetramethylsilane; C033353:pentane; C045798:2,2,4-trimethylpentane