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Protection against X-rays: lead-reduced but safe

Updated standard improves protection of medical staff and patients

PTB News 1.2016
Especially interesting for
  • manufacturers of protective devices against x-radiation
  • staff and patients in radiology and nuclear medicine

A new measurement method developed at PTB has been included in the updated version of the international series of standards IEC 61331. For the staff and the patients in medical X-ray diagnosis and nuclear medicine, the application of this standard, which has been elaborated under the leadership of PTB, represents a considerable improvement in radiation protection.

Old (top) and new (bottom) method compared: The intensity of the X-rays is measured by means of ionization chambers. The measured ratio of the radiation intensity with and without the test object shows how much a layer of material (test object) attenuates the X-rays (red). With the conventional narrow-beam geometry (NBG), the scattered radiation (blue) is not detected by the ionization chamber; with the new inverse broad-beam geometry (IBG), the flat ionization chamber can detect it.

Personal protective equipment and shielding (such as protective aprons, gloves and goggles as well as gonadal, testicle and ovary protection or even translucent protective plates such as lead glass plates) must comply with the series of standards IEC 61331 which lays down the requirements, testing procedures and markings.

For a long time, the protective effect of such equipment was solely based on lead (e.g. lead rubber or lead glass plates). This is why the designation “lead equivalent” has become common. It refers to the thickness of a layer of pure lead which would provide the same degree of attenuation as the material actually used (in a beam of a defined radiation quality and under specified geometric conditions).

In addition to lead rubber, materials which contain reduced lead or no lead at all have, for many years, been used for the manufacture of X-ray aprons. They offer the same protective effect but are up to 20 % lighter and also easier to dispose of. The determination of the lead equivalent value used so far was no longer suitable to describe the protective effect of these new materials appropriately. The new measurement method developed at PTB – inverse broad-beam geometry – consists of a flat ionization chamber which not only detects the primary radiation which is attenuated by the material sample, but also the scattered and fluorescence radiation on the side of the sample where the radiation is released. Since protective aprons are worn close to the body, this modified geometry is a good approximation of the real situation.

In the latest (2nd) edition of the IEC 61331 standard, this new procedure has now been made compulsory. Further improvements of the standard consist in the extension of the scope of application to photon-emitting radionuclides, in the definition of better suited radiation qualities for the tests, in the inclusion of all kinds of transparent radiation protection plates (not only lead glass), and in the inclusion of further protective equipment such as protective collars for the thyroid glands, protective goggles and masks for the eyes, and protective aprons for the dental X-ray region. For the staff and the patients in medical X-ray diagnosis and nuclear medicine, the consistent application of these second editions of the standard series IEC 61331 represents a considerable improvement in radiation protection.


Ludwig Büermann
Department 6.2 Dosimetry for Radiation Therapy and Diagnostic Radiology
+49 (0)531 592-6250


The standard

IEC 61331:2014, Protective devices against diagnostic medical X-radiation. Part 1: Determination of attenuation properties of materials. Part 2: Translucent protective plates. Part 3: Protective clothing, eyewear and protective patient shields