An efficient method for evaluating the lead equivalence of x-ray radiation protective equipment using an analytical spectrum model

Abstract

Background

X-ray radiation protective equipment is essential for ensuring the safety of medical staff. It is therefore important to verify its effectiveness, including confirming the specified lead equivalence (${\mathrm{Pb}}_{\mathrm{eq}}$), as it is a recognized standard protective value. Current methods require multiple comparative measurements with reference lead sheets, rendering the process laborious, susceptible to errors, and challenging to apply across a large medical facility with diverse protective equipment.

Purpose

To introduce an efficient method for evaluating lead equivalence based on a computational model involving analytical spectrum modeling.

Methods

The method consists of measuring the transmission of the protective equipment and then translating it into a lead-equivalent thickness using a computational model. In this work, an example implementation is presented utilizing the SpekPy toolkit for spectrum modeling. To validate the method, it was used to estimate the thickness of high-purity lead sheets with known thicknesses (0.1–1.0-mm Pb). Furthermore, its application is demonstrated for two lead-free aprons (0.25- and 0.35-mm ${\mathrm{Pb}}_{\mathrm{eq}}$), a lead-vinyl apron (0.5-mm ${\mathrm{Pb}}_{\mathrm{eq}}$), a lead–acrylic and a lead–plywood mobile screen (0.5- and 1.0-mm ${\mathrm{Pb}}_{\mathrm{eq}}$). Because the approach is based on measuring the transmission utilizing the primary x-ray tube beam (rather than scatter from a phantom), Monte Carlo (MC) simulations were performed to identify x-ray tube settings that reproduce clinically relevant scatter beams. Scatter spectra were simulated for different scatter angles (45${}^{\circ }$, 90${}^{\circ }$, 135${}^{\circ }$), tube voltages (60–120 kV), and filtration (0.1–1 mm added copper). Analytical primary spectra were then matched to scatter spectra in terms of first and second tenth-value layer (TVL) thicknesses in lead.

Results

The method is accurate to within approximately 3% and is suitable for both narrow and broad beams. For broad beams, it is necessary to scale the measured transmission by the buildup factor for lead, as the analytical spectrum model does not account for scatter. This factor, which transfers broad-beam air kerma to narrow-beam air kerma, ranges from 1.0 to 1.5 for 50–120-kV beams incident upon lead sheets with thicknesses of 0.1–1.0 mm. Without this factor, the lead equivalence can be underestimated by up to 28%. Using the method developed, it was found that the effectiveness of lead-free aprons decreases by up to 20% for high-kV and high-filtration beams, while other equipment investigated agreed more closely with specifications. The MC simulations of scatter spectra indicated that scatter beams are generally softer than primary beams, with a reduction in TVL by up to 54% (average of 25%). The entire range of scatter-mimicking primary beams can be realized with tube voltages 50–100 kV and less than 0.3 mm added copper filtration.

Conclusions

The method developed can accurately convert measured transmission into lead equivalence using a computational model, which eliminates the need to handle physical lead sheets. The transmission can be measured using recommended scatter-mimicking x-ray tube beams, derived here for a broader range of scatter angles and clinical beams with higher filtration than has previously been considered.