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     on matters related to measurement science and measurement standards.
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BIPM work programme: Ionizing Radiation

Since it was established, the BIPM Ionizing Radiation Department has set up and maintains the international reference standards that are used in the BIPM key comparisons of activity and dosimetry measurements for the NMIs, whose results are published in the KCDB in support of the CIPM MRA. The development and improvement of these standards constitutes a major part of our R&D programme.

The BIPM Ionizing Radiation Department delivers the following services to NMIs of Member States:

  • a worldwide unique international reference system (SIR) to permanently offer on request two ongoing key comparisons for activity of gamma emitters (on-site for short-lived radionuclides such as 99mTc and 18F with the SIR transfer instrument), as required for nuclear medicine diagnostics, imaging and therapy, environmental survey and nuclear cycle applications,
  • a worldwide unique system of high-stability reference instruments and facilities to permanently offer on-request eight ongoing key comparisons for dosimetry quantities and qualities of X-rays (low- and medium-energy and on-site accelerator beams), mammography, gamma-rays for radiotherapy and radioprotection levels and on-site HDR brachytherapy sources, and
  • characterizations of national standards of secondary level,
  • piloting/participation in international comparisons sponsored by the CCRI.
Ionizing radiation/Chemistry building

When the use of ionizing radiation in science, medicine and industry first became widespread it was clear that a world-wide system would be required to assure accuracy in measurement. In 1960, the 11th General Conference decided to establish the Ionizing Radiation Department at the BIPM.

The principal activities of the BIPM in the field of ionizing radiation are to maintain the international reference standards for dosimetry and activity measurements. These standards are used in the BIPM key comparisons and their development and improvement is a major part of the research and development programme. The NMI results are published in the key comparison database. The Department also undertakes characterizations of national standards for Member States, and participates in international comparisons under the auspices of the CCRI.

a hospital radiotherapy room

Accurate measurements of the effects of ionizing radiation are required in a wide range of industrial and medical applications where they are critical in decisions relating to human health and safety. In the field of dosimetry for radiotherapy, the accuracy required for such measurements is set by the need to avoid errors greater than the smallest detectable physiological effect.

measurement of a radionuclide before injecting a patient

In the areas needing activity measurements, nuclear medicine is perhaps the most stringent in its accuracy requirements. Generally this means that the uncertainty of measurements in hospitals should not exceed a few percent.

The fact that the accuracy sought is modest compared with that required in many other areas of metrology should not disguise the formidable difficulties that must be overcome to achieve this level of accuracy.

About 7 million radiotherapy patients are treated each year world-wide
Absorbed dose delivered: 2 Gy to 60 Gy
Dosimetry uncertainties:
  • Patient dosimetry: 2 %
  • Calibration laboratory: 1 %
  • Standards laboratory: 0.5 %
  • About 33 million nuclear medicine patients are diagnosed or treated each year world-wide
    Activity administered: 2 kBq to 20 MBq (diagnostic) and 200 MBq to 2 GBq (therapy)
    Activity uncertainties:
  • Administered activity: 5 %
  • Calibration laboratory: 2 %
  • Standards laboratory: 1 %
  • About 360 million patients are diagnosed using x-rays each year world-wide
    Absorbed dose delivered: 2 µGy to 10 mGy
    Dosimetry uncertainties:
  • Patient dosimetry: 5 %
  • Calibration laboratory: 3 %
  • Standards laboratory: 1 %
  • About 11 million people world-wide are monitored for personal dose because they work with ionizing radiation
    Personal dosimetry: few µSv to 50 mSv
    Dosimetry uncertainties:
  • Personal doses: 10 % (µSv) to 5 % (mSv)
  • Calibration laboratory: 2 %
  • Standards laboratory: 1 %

  • For more information about SI units in ionizing radiation, see section 2.2 of the SI Brochure.