Calculation of the humidity correction factor in air kerma strength measurement for 125I and 103Pd brachytherapy sources and its uncertainty by Monte Carlo method

Humidity is one of the sources of systematic error in the absolute measurement of air kerma strength of 125I and 103Pd low energy brachytherapy sources by using free air ionization chambers. In this paper, the humidity correction factor and its uncertainty for several environmental conditions have been calculated by applying an indigenous developed uncertainty analysis algorithm programmed in FORTRAN. The results of the analysis showed that the humidity could affect the corrected measured source strength value by about 0.2%.

► Humidity can affect the measurement of air kerma strength.
► Humidity correction factor “khumidity” values are calculated by using a Monte Carlo method.
► Humidity correction factors are calculated for 2% to 100% relative humidity.
► khumidity shows a minimum at 10% relative humidity and a maximum at 100%.
► The uncertainty in khumidity is calculated to be about 0.2% for 125I and 103Pd sources.