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Quality assurance

Dosimetry audits for safe and effective radiotherapy treatment

Joanne Liou

Radiotherapy is required for nearly half of all cancer patients, and the precise delivery of radiation — the amount and the localization — is key to the success of the treatment.

“The accuracy of the dose delivered to cancer patients is directly related to the outcome, both in terms of tumour control and in sparing healthy tissue to the extent possible,” said Jamema Swamidas, Head of the IAEA’s Dosimetry Laboratory. “It is, therefore, extremely important to deliver an accurate dose, not only in terms of quantity, but also to the precise location of the tumour.”

Dosimetry is the science of measuring, calculating and assessing radiation doses, and dosimetry auditing ensures that radiation doses to patients are accurate and delivered with well calibrated machines. While some countries manage their own audit programmes, in those that do not, the IAEA — together with the World Health Organization (WHO) — has, since 1969, provided audit services to independently verify the calibration of radiotherapy units.

Radiotherapy technology is evolving rapidly. We need to keep developing new methodologies to keep pace with new techniques.”
Jamema Swamidas, Head, IAEA’s Dosimetry Laboratory

The IAEA–WHO audit programme

The IAEA’s Dosimetry Laboratory in Seibersdorf, Austria, performs about 800 to 900 audits of radiotherapy beams per year for more than 130 countries. To date, the service has performed approximately 15 000 radiotherapy beam checks around the world, Swamidas said.

Participating medical physicists provide details about their radiotherapy machines when an audit is requested, and the IAEA sends dosimeters — devices used to measure absorbed doses of ionizing radiation — to radiotherapy facilities or national coordinators for distribution. The dosimeters are then irradiated to a specified dose, similar to how a patient would be treated. Afterwards, the dosimeter is sent back to the Dosimetry Laboratory for evaluation, where the amount of radiation the dosimeter received is compared with the dose originally stated.

A measurement recorded within five per cent of the specified dose is acceptable. “Anything outside the acceptable range is investigated. We assist hospital medical physicists to resolve any misunderstandings or discrepancies,” Swamidas said. For regular participants, it takes about four to six months to complete the audit, from the application for an audit to the availability of results. However, the turnaround for urgent requests is much faster.

“For over 20 years, we have been benefiting from IAEA–WHO postal dosimetry audits that ensure the quality of basic dosimetry,” said Tatiana Krylova, Head of Medical Physics at the N.N. Blokhin Russian Cancer Research Centre in Moscow.

Developing audit methodology

Through coordinated research projects (CRPs), the IAEA is continuing to develop methodologies for dosimetry audits. “Radiotherapy technology is evolving rapidly,” Swamidas said. “We need to keep developing new methodologies to keep pace with new techniques.”

Last year, the IAEA launched a five-year CRP to verify the dosimetry of high dose rate brachytherapy, a type of internal radiation therapy used to treat gynaecological cancer. “Through this research project, the IAEA will coordinate the development of a methodology to audit the brachytherapy process used in the management of cervical cancer,” Swamidas said. Many low and middle income countries have a high incidence of cervical cancer, and the project builds upon four previous CRPs that have helped develop and disseminate auditing methodologies for radiotherapy techniques.

February, 2022
Vol. 63-1

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