title: Proton beam output measurement with an extrapolation chamber.
abstract: A variable air-volume, parallel-plate extrapolation chamber forming an integral part of a polystyrene phantom was used in measurement of dose rate in a 250 MeV clinical proton beam. The sensitive air-volume of the extrapolation chamber is controlled through the movement of the chamber piston by means of a micrometer mounted on the phantom body. The relative displacement of the piston is monitored by a calibrated mechanical distance travel indicator. The proton beam dose rate determined with the uncalibrated extrapolation chamber was 5% lower than the dose rate determined with a calibrated Farmer-type thimble chamber at the same depth in the polystyrene phantom. Despite the current 5% discrepancy, uncalibrated extrapolation chambers may offer a simple and practical alternative to current techniques used in output measurements of proton beam machines.
authors.affiliation: Department of Medical Physics, McGill University, Montréal, Quebéc.
authors.forename: C
authors.initials: C
authors.lastname: Zankowski
authors.forename: S
authors.initials: S
authors.lastname: Vatnitsky
authors.forename: J
authors.initials: J
authors.lastname: Siebers
authors.forename: E B
authors.initials: EB
authors.lastname: Podgorsak
mesh_terms: D002138:Calibration; D019047:Phantoms, Imaging; D011522:Protons; D011879:Radiotherapy Dosage; D011882:Radiotherapy, High-Energy
chemical_list: D011522:Protons