The temporal and spatial (partial volume) response characteristics of ionization chambers used for measuring radiation exposures in x-ray quality control (QC) programs were evaluated. Five ionization chambers were evaluated using a pencil beam scanning x-ray source and a conventional radiographic system. The spatial response was determined by recording the exposure during scanning of the pencil beam or in increments using a slitted lead sheet on a conventional x-ray system. The temporal response was determined by recording x-ray wave forms using the different ionization chambers. The effects of partial volume irradiation of the chambers makes them unsuitable for use under these conditions, except those designed for exposure measurements in computed tomography. The temporal response of many chambers resembles that of a typical resistive-capacitive circuit, making them unsuitable for exposure time measurements or x-ray wave form evaluation. The appropriate ionization chamber must be selected for exposure measurements and quality control in diagnostic radiology.
