The NPL Radionuclide Calibrator (Fidelis)

In the UK, around half a million patients a year undergo diagnostic procedures involving the use of radionuclides. In addition, some 30,000 patients receive high activities of radionuclides for treating various conditions and for pain palliation. NPL aims to support the regulations that ensure that activities of radionuclides administered to the patients are as low as practicable, compatible with the medical procedure.

Radionuclides are playing an expanding role in medicine due to the ability to obtain images of physiological function. Advances in biotechnology are also leading to the development of drugs that target cancer cells; attaching a radionuclide to a carrier molecule that seeks out the cancerous cells enables the cancer to be destroyed, sparing the surrounding healthy tissue.

For compliance with regulations, the activity administered to the patient should be within 10% of the prescribed activity. The activity in the drug is normally checked at the hospital prior to injection using an ionisation chamber (a 'radionuclide calibrator'). NPL is working on several projects to support these measurements:

• Standardisation of medically important radionuclides (for example, Tc-99m), comparison of these standards with those held at other national measurement institutes, and running of measurement services based on the new standards.
• Derivation and dissemination of new calibration factors for the NPL 'Fidelis' Radionuclide calibrator.
• Use of new internet technology to support the measurement infrastructure.
• Standardisation of radionuclides undergoing clinical trials in order to provide a measurement service for these radionuclides in the long term.
• Establishment of a new measurement service for short lived radionuclides used in Positron Emission Tomography.
• Running the Radionuclide Calibrators Users Forum – to facilitate best practice in measurement.
• National Comparison Exercises to demonstrate the proficiency of nuclear medicine departments at assaying the radioactivity content of the radiopharmaceuticals (see below).

Results from the 2009 national comparison exercise for ⁹⁰Y. The number of results is shown on the y-axis.
Results range from 0.1 to 2 times the true sample activity (1.0 on the plot).

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