Radiation doses in interventional radiology procedures: The RAD-IR study Part III: Dosimetric performance of the interventional fluoroscopy units

PURPOSE: To present the physics data supporting the validity of the clinical dose data from the RAD-IR study and to document the performance of dosimetry-components of these systems over time. MATERIALS AND METHODS: Sites at seven academic medical centers in the United States prospectively contributed data for each of 12 fluoroscopic units. All units were compatible with International Electrotechnical Commission (IEC) standard 60601-2-43. Comprehensive evaluations and periodic consistency checks were performed to verify the performance of each unit's dosimeter. Comprehensive evaluations compared system performance against calibrated ionization chambers under nine combinations of operating conditions. Consistency checks provided more frequent dosimetry data, with use of each unit's built-in dosimetry equipment and a standard water phantom. RESULTS: During the 3-year study, data were collected for 48 comprehensive evaluations and 581 consistency checks. For the comprehensive evaluations, the mean (95% confidence interval range) ratio of system to external measurements was 1.03 (1.00-1.05) for fluoroscopy and 0.93 (0.90-0.96) for acquisition. The expected ratio was 0.93 for both. For consistency checks, the values were 1.00 (0.98-1.02) for fluoroscopy and 1.00 (0.98-1.02) for acquisition. Each system was compared across time to its own mean value. Overall uncertainty was estimated by adding the standard deviations of the comprehensive and consistency measurements in quadrature. The authors estimate that the overall error in clinical cumulative dose measurements reported in RAD-IR is 24%. CONCLUSION: Dosimetric accuracy was well within the tolerances established by IEC standard 60601-2-43. The clinical dose data reported in the RAD-IR study are valid.