Use of secondary air kerma from dose area product and fluoroscopy time for preventive effective dose estimation in interventional radiology procedures for staff

Introduction: interventional radiology workers are potentially exposed to high levels of ionizing radiation, therefore preventive dose estimation is mandatory for the correct risk classification of staff. Effective dose (ED) is a radiation protection quantity strictly related to the secondary air kerma (K (S)), using appropriate multiplicative conversion factors (ICRP 106). The aim of this work is to evaluate the accuracy of K (S) estimated from physically measurable quantities such as dose-area product (DAP) or fluoroscopy time (FT). Methods: radiological units (n = 4) were characterized in terms of primary beam air kerma and DAP-meter response, consequently defining a DAP-meter correction factor (CF) for each unit. K (S), scattered from an anthropomorphic phantom and measured by a digital multimeter, was then compared with the value estimated from DAP and FT. Different combinations of tube voltages, field sizes, current and scattering angles were used to simulate the variation of working conditions. Further measurements were performed to estimate the couch transmission factor for different phantom placements on the operational couch, defining a CF as the mean transmission factor. Results: when no CFs were applied, the measured K (S) showed a median percentage difference of between 33.8% and 115.7% with respect to K (S) evaluated from DAP, and between -46.3% and 101.8% for K (S) evaluated from FT. By contrast, when previously defined CFs were applied to the evaluated K (S), the median percentage difference between the measured K (S) and the value evaluated from DAP ranged from between -7.94% and 15.0%, and between -66.2% and 17.2% for that evaluated from FT. Conclusion: when appropriate CF are applied, the preventive ED estimation from the median DAP value seems to be more conservative and easier to obtain with respect to the one obtained from the FT value. Further measurements should be performed with a personal dosimeter during routine activities to assess the proper K (S) to ED conversion factor.