Correction factors applied to plane-parallel ionization chambers
1993 (English)In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 38, no 2, 311-322 p.Article in journal (Refereed) Published
Plane-parallel ionization chambers are recommended by most dosimetry protocols' for use in low-energy electron beams. Such chambers are often calibrated at the clinic against a cylindrical chamber in a high-energy electron beam while no general procedures for Co-60 gamma-ray calibrations are yet adopted. If the perturbation due to the presence of the plane-parallel chamber in a water phantom at the calibration quality, i.e. Co-60, is known, a straightforward dose-to-water calibration would be possible. Furthermore, if the perturbation as a function of photon beam quality is known, the plane-parallel chamber might be used for all radiation qualities (both electrons and photons) used in megavoltage therapy. In this work the response of both plane-parallel and cylindrical chambers was studied and compared with ferrous sulphate dosimetry over a wide range of photon energies. Perturbation correction factors were determined for these chambers in photon beams. Also the influence of the aluminium central electrode of the NE2571 chamber was determined in the electron field relative to Co-60 gamma-radiation. Electron backscatter from the back wall of the chamber was shown to influence the signal in the chamber significantly. A procedure for calibration of Co-60 gamma-rays in water in plane-parallel chambers is discussed.
Place, publisher, year, edition, pages
1993. Vol. 38, no 2, 311-322 p.
IdentifiersURN: urn:nbn:se:umu:diva-39965DOI: 10.1088/0031-9155/38/2/008ISI: A1993KM27800008OAI: oai:DiVA.org:umu-39965DiVA: diva2:396931