Purpose: Currently, lead-free x-ray-protective clothing is classified by the European production standard EN 61 331-3. To evaluate protective effects of lead-free materials according to this standard, the certifying offices as well as customers solely refer to the lead equivalent (LE). The LE of lead-free protective clothing, however, depends on the tube voltage (energy spectrum). Therefore, stating a single value for x-ray-protective clothing does not reveal the protective efficacy for the complete range of energy as applied in clinical practice. Moreover, the method of narrow beam geometry does not account for information on secondary radiation (scattered and fluorescent radiation) generated within the material. Lead-free materials, however, generate large-scale fluorescent radiation, especially for elements with atomic numbers below 60. As a consequence, full-scale secondary radiation of a given material can only be detected with a broad beam setup.
Materials and methods: In accordance with IEC 61 331-1, we compared commercially available radiation-protective aprons manufactured with lead-free or partially lead-free materials with aprons manufactured on a lead-oxide basis. In addition to the LE, attenuation ratios and dose-build-up-factors under broad beam-conditions were evaluated.
Results: In comparison with lead-oxide materials, protection efficacy of lead-free materials is reduced by up to 70 %, particularly for a tube voltage below 80 kV. Lead-composite materials (partially lead-free materials) are less affected.
Conclusion: Users and patients wearing lead-free x-ray-protective clothing might unknowingly be exposed to a much larger dose than generally assumed. In the future, radiation protection rating should exclusively refer to the "attenuation ratio", which is based on broad beam geometry and characterizes radiation attenuation much more precisely than the lead equivalent.