Air density dependence of the response of the PTW SourceCheck 4pi ionization chamber for 125I brachytherapy seeds

The effect of overestimation observed in the chamber responses once they are corrected for the standard pressure and temperature may represent a non-negligible ∼4% overestimation in high altitude cities as ours (700 m AMSL). This overestimation behaves linearly with the air density in all cases analyzed.