Cari Borras DSc, Presenter: Nothing to Disclose

William A. Roventine MS, Abstract Co-Author: Nothing to Disclose

Lisa J. McAuley MS, Abstract Co-Author: Nothing to Disclose

The usefulness and limitations of two newly available diagnostic radiology dosimetry systems, which incorporate solid-state detectors, were assessed by comparing measurements made with these detectors with those obtained with two conventional ionization chamber/electrometer systems using standard AAPM and ACR protocols.

Measurements with and without scatter at various beam qualities and using different geometries were made in radiographic, fluoroscopic and mammographic modes. Three solid state detectors were used: Unfors Xi RF + Mammo Detector, Barracuda (RTI Electronics) MPD (multipurpose detector for radiography and mammography measurements), and Barracuda RB100 detector (for fluoroscopy). The electrometers/ionization chambers used were a Keithley Triad TNT with a model 96035 B dual entrance window ion chamber and two RadCal model 1015 electrometers with 10X5-6 ion chamber for radiography and fluoroscopy and 10X5-6M chamber for mammography. All the systems had either been sent to a calibration laboratory or to their respective manufacturers for calibration; the stated accuracies ranged from ±3 to ±5%.

The Barracuda systems always read lower than the ionization chambers; the Unfors system read about the same or lower, except in mammography where it read up to 5% higher. The greatest deviations between the solid state detector and ion chamber readings were as follows: radiography, Unfors -12%, Barracuda -68%; fluoroscopy, Unfors ±2%, Barracuda -23%; mammography, Unfors +5%, Barracuda -28%. The differences were ascribed to differences in scatter and angular dependence between the various types of detectors. The complete list of results and measurement conditions will be shown and analyzed.

Solid state detectors are very convenient as a quality control tool to assess x-ray machine output. However, it is necessary to develop measurement protocols which take into account the characteristics of the detectors if reasonable dosimetry accuracy is to be expected.

Accurate dosimetry is important to compare institutional values with diagnostic reference levels and it is critical in the case of mammography and fluoroscopy, where dose or dose rate limits exist.

Borras, C, Roventine, W, McAuley, L, Solid State Detectors versus Ionization Chambers for Diagnostic Radiology Dosimetry.  Radiological Society of North America 2007 Scientific Assembly and Annual Meeting, November 25 - November 30, 2007 ,Chicago IL. http://archive.rsna.org/2007/5009708.html