An evaluation of semiconductor and ionization chamber detectors for diagnostic x-ray dosimetry measurements.

Dosemeters for performance testing of x-ray equipment may utilize semiconductor technology or ionization chambers (ICs). Semiconductor dosemeters incorporate several elements into the detectors from which compensation for variations in response with photon energy is derived. The design of the detectors influences their response with angle and this is different from that of ICs. The responses of semiconductor detectors (SDs) and ICs to x-ray beams with a variety of radiation qualities have been measured in order to assess differences in response. Measurements have been made with experimental arrangements simulating use of the detectors in performance testing of digital radiography and fluoroscopy equipment. Results show that differences in photon energy responses between the detectors are small, but because ICs are sensitive to radiation incident from all angles, they record more scattered radiation than SDs. Implications of differences in detector responses are discussed and recommendations made about their use. SDs are more appropriate for measurements of image receptor doses and are recommended for setting up automatic exposure control devices for digital radiography. ICs are suitable for assessment of patient entrance surface dose rate measurements. Correction factors that could be applied to allow comparisons between measurements with different dosemeters are proposed.