Re-evaluation of the BIPM international dosimetry standards on adoption of the recommendations of ICRU Report 90

Abstract

Abstract Following the recommendations of ICRU Report 90, a re-evaluation has been made of the BIPM standards for air kerma in x-rays and in 60 Co and 137 Cs γ -radiations, for absorbed dose to water in 60 Co γ -radiation and for reference air-kerma rate in 192 Ir γ -radiation for brachytherapy. The changes arise from three sources: (i) the implementation of new correction factors k ii and k W for free-air ionization chambers; (ii) a re-evaluation of the mean excitation energy for graphite and water and the density effect for graphite; (iii) new stated uncertainties for the value of W air for dry air and for the related product W air s g,air . Consideration has also been given to new recommendations for photon interaction coefficients, although no corresponding changes have resulted. The heat defect in graphite is also considered. A summary table of the combined effect of these changes is presented. The new standards will be implemented on 1 January 2019.