Absorbed dose in water and air

An ageing population is likely to mean that Europe’s health services will each need to strengthen and broaden patient access to radiotherapy treatments. Each year, around four million new cases of cancer come to light, requiring the large-scale provision of radiotherapy diagnoses and treatments in each nation.

The goal for each patient is to kill tumour cells while causing as little harm as possible to surrounding healthy cells. However, small percentage variations in radiation dose can significantly amplify the risk of side effects; changes in dose of just 5 % increases the chance of damage to healthy cells by as much as 20 % to 30 %. What’s more, in practice the standard level of accuracy for delivered doses of 2.5 % is difficult to achieve, due to differences in calibration and treatment conditions, leaving fine margins for error. Regional differences across Europe also meant that many treatment centres did not have access to suitable calibration services able to ensure continual accuracy in line with national primary standards.

This project brought NMIs with experience in providing x-ray dosimetry measurement services together with NMIs of emerging EU Member States, to develop accurate measurement devices, known as dosemeters, and developed a network of primary laboratories able to transfer primary reference standards to local calibration laboratories. These primary standards were either cavity or free air ionisation chambers, used for high and low-to-medium photon radiation energies respectively, or calorimeters used to measure absorbed doses.

The project developed improved calibration practices and primary dosimeter standards. By attending workshops, training courses, and by producing good practice guides, NMIs and DIs previously reliant on secondary standards developed expertise in designing, building and operating primary dosimeters based on water calorimeters, cavity ionisation chambers and free air ionisation chambers. Around 20 other institutions also collaborated, mainly hospitals, to develop skills in uncertainty reduction and calibration methods. The partners contributed to developing harmonised uncertainty budgets, reaching 0.5 % and 2.0 % for the reference value in terms of air kerma (kinetic energy released per unit mass) and absorbed dose to water, respectively.

Developing calibration services involved obtaining reference values from primary or secondary standards, participation in inter-comparisons, ISO 17025 accreditation, and publication in BIPM’s key comparison database for Calibration and Measurement Capabilities (CMCs). New CMCs so far reported include improved traceability for radiation protection, diagnostic imaging and cancer radiation treatment in Belgium, and new services at NMIs in Croatia, Poland and Serbia.

An example beneficiary is the Serbian Institute of Occupational Health, accredited to perform tests of mammography x-ray machines for Quality Assurance purposes as a result of new local x-ray calibration services provided by Vinca Institute of Nuclear Sciences (VINS).

These new capabilities have started to harmonise calibration procedures in line with international standards, leading to safer and more effective radiotherapy treatments across Europe.