Radiation Dosimetry

Dosimetry in medicine and radiation protection

Ensuring comparability of radiation dose measurements

Accurate radiation dose measurements are essential in radiotherapy, medical imaging and radiation protection. They enable the accurate delivery of prescribed doses to patients in radiotherapy, while in medical imaging they are used to assess and optimise radiation exposure while maintaining image quality. Beyond these clinical applications, accurate measurements are also needed in radiation protection to assess and control exposure to ionizing radiation.

Ensuring the accuracy and comparability of these measurements requires well-established and internationally recognised measurement standards.

The BIPM maintains high-accuracy primary standards and provides comparison and calibration services that allow National Metrology Institutes (NMIs) to demonstrate the equivalence of their primary standards or obtain traceability for their secondary standards to the International System of Units (SI).

The BIPM’s work in radiation dosimetry

BIPM reference standards for radiation dosimetry

Applications of ionizing radiation require accurate measurements under different radiation conditions and at different energies. The BIPM maintains high-accuracy primary standards and reference radiation fields across a carefully selected range of photon energies, and provides comparison and calibration services that enable National Metrology Institutes (NMIs) to demonstrate the equivalence of their primary standards or establish traceability to the SI over a wide energy range.

Technical services and resources

Dosimetry comparisons, calibrations and reference conditions

Access BIPM comparison and calibration services and reference information for radiation dosimetry.

What is radiation dosimetry?

Radiation dosimetry concerns the realization, measurement and dissemination of absorbed dose and related radiation dose quantities. Accurate and traceable dosimetry underpins the reliable use and measurement of ionizing radiation across a wide range of applications, including radiotherapy, medical imaging, radiation protection, industry and scientific research.

Why does the BIPM use different radiation beams and primary standards?

Different applications require measurements under different radiation conditions and at different energies. The BIPM therefore maintains primary standards and reference radiation fields for carefully selected radiation qualities so that national standards can be compared or calibrated against appropriate international references. The Consultative Committee for Ionizing Radiation (CCRI) coordinates international work in this area, including the selection of reference radiation qualities used for international comparisons.

What is absorbed dose to water?

Absorbed dose to water measures the energy deposited by radiation per unit mass of water. It is a principal reference quantity for radiotherapy dosimetry.

What is air kerma?

Air kerma is a fundamental dosimetric quantity used to characterize x-ray and gamma-ray radiation fields. It is used as a reference quantity for measurements in applications including diagnostic imaging and radiation protection.

Why are international dosimetry comparisons important?

International dosimetry comparisons allow National Metrology Institutes (NMIs) and Designated Institutes (DIs) to demonstrate the equivalence of their national primary standards by comparison with international reference values. The results also provide evidence for internationally recognized Calibration and Measurement Capabilities (CMCs) under the CIPM Mutual Recognition Arrangement (CIPM MRA).

How does the BIPM provide dosimetry services using external facilities?

Some BIPM dosimetry services are provided using external facilities that have been fully characterized by the BIPM. These services are based on BIPM primary standards. High-energy photon services use reference beams at the DOSEO scientific platform in Saclay, France, while radiation-protection dosimetry services use the International Atomic Energy Agency (IAEA) caesium-137 irradiation facility in Seibersdorf, Austria.