Calibration of plane parallel ionization chambers at 60Co gamma beam for radiotherapy dosimetryAim of the studyThe aim is to determine the accuracy and reliability of the calibrations of plane parallel chambers for the dose measurements at radiotherapy electron beams when the calibration is carried out at a 60Co gamma beam. From 1999 the plane parallel chambers have been calibrated at radiotherapy electron beams because of the differences between the characteristics of individual chambers within a given chamber type. However, the characteristics of the chambers have been improved in the last few years and the possibilities to return to the simpler calibration at a 60Co gamma beam will be investigated. ImplementationPlane parallel chambers will be calibrated in accordance with the IAEA Code of Practice (TRS 398) for absorbed dose to water in a water phantom both at a 60Co gamma beam of the standard dosimetry laboratory of STUK and at radiotherapy electron beams (16-20 MeV). The water phantom for the calibration will be reconstructed with the setting of the chamber at the required depth with a laser beam. The results will be used to analyse the accuracy and reliability of the calibration at a 60Co gamma beam and other consequences of the change of the calibration method. Dissemination and exploitation of the resultsThe results are published as STUK STO-TR reports and as a part of the quality manual of the standard dosimetry laboratory (uncertainty estimates). Information on the method of calibration is distributed at the annual meetings with radiotherapy physicists. The change of the calibration method reduces calibration uncertainty and simplifies the calibration method. CollaboratorsRadiotherapy departments in Finland Timetable2008 Responsible scientistIlkka Jokelainen Page updated 17/05/2009
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