Lung counting: a function to fit counting efficiency of a lung counting germanium detector array to muscle-equivalent-chest-wall-thickness and photon energy using a realistic torso phantom

A function has been developed that will fit counting efficiency to chest wall thickness, adipose content of the chest wall, and photon energy. The adipose content of the chest wall is removed as a variable by use of the derived quantity: muscle equivalent chest wall thickness. The function has been tested on experimental data sets obtained from the LLNL and JAERI torso phantoms using a variety of germanium detector lung counting systems. The function is applicable over the range of existing phantoms and the range of equipment types tested. Subtle differences between the detector systems are shown by differences in the fit parameters. This analysis could be a useful addition to lung counting analysis software. The LLNL and JAERI phantoms have very similar counting characteristics as evidenced by the similarity of the function parameters when measured using a single detector system.