Development of a calibration facility for test instrumentation in diagnostic radiology

The establishment and application is described of a number of standard IEC radiation qualities (IEC 1267: 1994-09) for the calibration of test instrumentation used in patient dose auditing in diagnostic radiology. Comparisons are drawn between two primary dosimetry systems of traceability represented by: (i) the NPL protection level air kerma standard in conjunction with an RRPPS calibrated diagnostic dosemeter, and (ii) PTB calibration of the same diagnostic dosemeter using the PTB diagnostic primary standard. Although the NPL protection level standard can be used (RRPPS/NPL calibration route +/-5% at the 95% CL) significant reduction in uncertainty is available through use of the PTB diagnostic primary standard (+/-4% at the 95% CL). Calibration of kV(p) is also described, covering both mammographic spectra (25 kV(p) up to 35 kV(p)) and general radiographic spectra (50 kV(p) up to 120 kV(p)); uncertainties of 3% and 1% respectively are estimated at 95% CL.