An analysis of calibration coefficients measured in water and in air for Farmer-type cylindrical ionization chambers

A comparison of calibration coefficients of Farmer-type cylindrical ionization chambers calibrated in a Co-60 beam according to the IAEA Reports 277 and 398 formalisms. 91 calibration coefficients measured in air and in water. The 398ND,W/277ND,W ratios were calculated, taking into account the wall material of the chambers. The correlation between 398ND,W and NK, ND,air 277ND,W was made and the equations of the regression straight lines were determined.Calibration coefficients, determined according to the IAEA Report 398, are higher by about 1% than those determined according to the IAEA Report 277, and they depend slightly on the wall material of the chamber. The introduction of the IAEA dosimetry Report 398 resulted in an increase in the doses delivered to patients by about 1% as compared with the period of application of Report 277. The regression equations may assure increased accuracy in retrospective comparative calculation of doses according to both reports as compared with the correction based on mean percent values. (author)