On the (f)utility of measuring the lead equivalence of protective garments

Purpose: Protective garments incorporating lead (Pb) or other moderate to high atomic number elements are a necessary radiation protection tool. However, as lead has been replaced by other elements, verifying manufacturers' claims regarding the lead equivalence of such garments has become nearly impossible, and current standards only require measurement of attenuation or lead equivalence at a single beam quality. A garment may provide a high degree of protection at the specified beam quality, but underperform at others. The authors sought to measure the lead equivalence of several protective garments and propose a better method for quantifying the protective value of garments. Methods: The authors measured the penetration of primary and scattered radiation through lead sheets and three protective garments of nominal 0.5 mm Pb equivalence, one lead and two lead-free. Penetration was measured using beams of nominal 60, 80, 100, and 120 kVp. Primary penetration through protective garments at 70 kVp was also measured. A lead-lined enclosure was constructed for measuring scatter penetration, as instruments must be protected from stray radiation when measuring low-level penetration of scattered radiation. Using polynomial least-squares fits to the measured data of penetration through lead sheets, the authors determined the lead equivalence of the protective garments across a range of beam qualities. Results: The lead garment was 0.5 mm Pb equivalent across all beam qualities evaluated. While the maximum lead equivalence of the lead-free garments did occur at the manufacturer-specified beam quality, neither garment was 0.5 mm Pb equivalent at the specified beam quality. The lead equivalence of the lead-free garments was a strong function of beam quality and nature of the radiation, i.e., primary or scattered. The lead equivalence of the lead-free garments in primary beams ranged from 0.40 to 0.47 mm Pb equivalent and in scattered beams ranged from 0.37 to 0.46 mm Pb equivalent. The penetration through one lead-free garment at 60 kVp was 478% higher than the penetration through the lead garment. The authors have also provided linear fits of radiation penetration through lead as a function of half-value layer. It is likely that assessment of protective value can be performed using primary beams matched to the spectra of scattered beams. The authors propose the diagnostic radiation index of protection (DRIP), a weighted sum of the percentage of radiation penetration across a range of beam qualities, as a more robust method for specifying the protective value of garments. Conclusions: The protective value of garments from both primary and scattered radiation is a strong function of beam quality. Assessment of the protective value should be performed across a range of beam qualities. Methods for performing such assessment must be developed and must specify beam qualities, measurement geometry, and the appropriate weighting across the beam quality range for different applications.