International cooperation to ensure worldwide uniformity in dosimetry

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The Physikalisch-Technische Bundesanstalt regularly takes part in international key comparisons. These are comparison measurements at the highest level of accuracy; they serve to prove that the German national standard for the unit of absorbed dose to water is equivalent to the primary standards of other metrology institutes.

These key comparisons, which usually have to be repeated at least every 10 years, are organized by the Bureau International des Poids et Mesures (BIPM). All national metrology institutes which have a primary standard for the corresponding quantity participate in these comparisons.

The results of these key comparisons are published in the Journal "Metrologia" and can be viewed on the BIPM's website in the key comparison database (KCDB).

Apart from these key comparisons at the highest accuracy level, PTB works in close cooperation with other national metrology institutes within the scope of international research projects, in order to, e.g., jointly develop new dosimetric processes for modern methods of radiotherapy and, thus, ensure the international uniformity of dosimetry. A current example of such a cooperation is the project "Metrology for MR guided Radio Therapy" which is funded by the European Union within the scope of the "European Metrology Programme for Innovation and research (EMPIR)", in which PTB, together with 8 other European research institutes, develops new and more accurate dosimetric processes for modern radiotherapy.

With their knowledge and experience, PTB employees are able to contribute actively to elaborating international standards and guidelines in the field of dosimetry. An example of this is the directives issued by the International Atomic Energy Agency (IAEA) below: 

• TRS-398: Absorbed Dose Determination in External Beam Radiotherapy. An International Code of Practice for Dosimetry Based on Standards of Absorbed Dose to Water,
• TRS-496: Calibration of Reference Dosimeters for External Beam Radiotherapy,
• IAEA-TECDOC-1585: Measurement Uncertainty. A Practical Guide for Secondary Standards Dosimetry Laboratories,

which were elaborated with PTB's active collaboration.

As an affiliated member of the international network of Secondary Standards Dosimetry Laboratories (SSDL network) which is organized by the IAEA and in which more than 80 dosimetry laboratories from 67 countries are currently cooperating with each other, PTB, together with other national metrology institutes, ensures the external quality assurance of the dosimetry comparisons which are regularly carried out in this network. This allows the dose measurements performed within the scope of these comparison measurements to be traceable to the International System of Units (SI).