15 September 2026
Radiotherapy treatments in Australia, New Zealand and several Southeast Asian countries are set to receive even greater assurance as a water calorimeter primary standard will soon replace the existing graphite measurement device.
Almost five years in the making, the water calorimeter will become Australia’s primary standard for ionising radiation in 2027.
Significant progress has been made in this project.
It started in 2022 with a review of international solutions to identify the appropriate instrument for Australia. The team has now worked for several years installing, calibrating and testing the new instrument says the Australian Radiation Protection and Nuclear Safety Agency’s (ARPANSA) chief medical radiation scientist, Dr Ivan Williams.
‘Our most recent test of the water calorimeter resulted in a measurement within 0.3 per cent of the international standard, demonstrating that the device is almost ready to replace the current graphite primary standard,’ Dr Williams said.
'We’re now establishing verifiable consistency of measurement which is necessary to retire the old instrument and formally transfer the Primary Standard role to the new instrument.
‘Medical physicists in cancer centers use instruments, with a calibration traceable to the Primary Standard, to ensure that the radiation dose being delivered to the patient is correct. So getting this right is vital.
‘The human body more closely resembles water than graphite, so measuring radiation dose directly in water reduces uncertainties and provides a more accurate picture of the doses patients receive during treatment,’ Dr Williams said.
ARPANSA will continue to benchmark the water calorimeter measurements with the International Bureau of Weights and Measures (BIPM) in Paris. ARPANSA will do this until Australia’s primary standard and the international one are aligned.
Our primary standard protects patients who receive radiotherapy treatment by ensuring that doses are not more or less than what the doctor has prescribed.
Background
The new primary standard, designed and installed by the Canadian National Research Council must be operated at 4°C to accurately measure the very small temperature rises produced by the interaction of ionising radiation beam with the water. For a typical radiation therapy prescription, this is less than 1/1000th of a degree, requiring a very sensitive detection system capable of sub-micro degree measurement. The heart of the calorimeter is a glass vessel filled with hyper-pure water, saturated with hydrogen gas. This provides a very well-controlled medium in which the absorbed dose can be measured accurately.
Learn more about our primary standard dosimetry laboratory on our website: https://www.arpansa.gov.au/our-services/testing-and-calibration/calibration/psdl
For more information about the device and its journey to ARPANSA, go to this website: https://nrc.canada.ca/en/stories/metrology-experts-australia-collaborating-new-radiation-therapy-tool
