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New Dosimetry Audit Service for Linacs Used in Radiotherapy


IAEA team involved in electron beam audit development at the Agency’s Seibersdorf laboratories. IAEA/WHO dosimetry audit service offered to radiotherapy centres around the world now includes high energy electron beams for newly installed linacs. (Photo: L. Czap/IAEA)

The IAEA and the World Health Organization (WHO) have rolled out a new type of dosimetry audit as a cost-free service to radiotherapy centres around the world to support hospitals in tackling the growing cancer burden.

Since its launch in 1969, the IAEA/WHO audit service has been limited to checking high-energy photon beams, while the number of medical linear accelerators, or linacs, capable of delivering both photon and electron radiation beams has been steadily increasing. According to the IAEA DIrectory of RAdiotherapy Centres (DIRAC), about half of radiotherapy treatment units installed globally since 2010 can produce clinical electron beams. These beams are commonly used for treating anatomical sites close to the patient’s surface, such as skin lesions or tumour beds after surgery. The new electron beam audit service will help to ensure that such treatments are performed safely and effectively.

Quality assurance programmes for radiotherapy processes are established to guarantee that the dose delivered to the target inside a patient undergoing radiotherapy is correct. Too high dose of radiation can be harmful to surrounding healthy organs, while a dose that is too low may not be efficient in killing cancer cells. Verifying the calibration of the treatment unit is the cornerstone of radiotherapy quality assurance, and external dosimetry audits have been widely recognized as an invaluable tool for quality control of the calibration and are mandatory in some countries.

“I have participated in the IAEA external audit for photon beams for decades. The addition of the electron beam to the service is a great step,” said Paola Alvarez from the Imaging and Radiation Oncology Core (IROC), Houston Quality Assurance Center, MD Anderson Cancer Center, USA, a member of the Dosimetry Audit Network. “The audit is performed in the same way as the beam calibration which makes the irradiation of the detectors fast and simple.”

The IAEA/WHO provides an external dosimetry audit service using special dosimeters shipped to participating hospitals, and the dosimeters are then irradiated in typical radiation treatment conditions at the hospital to a specified dose. The dosimeters are then sent back for evaluation to the IAEA to compare the actual dose the dosimeter was exposed to with the dose that was planned. Results within 5% of the target are considered acceptable, while any larger deviations are followed up by the IAEA dosimetry audit team. After carrying out any corrective actions necessary, the audit is repeated.

Lora Ioannou and Stefani Stefanou, Radiotherapy Medical Physicists from Bank of Cyprus Oncology Centre in Nicosia, have relied on the IAEA for dosimetry audits of the photon beams in their hospital for many years. “We welcome the expansion to electron beam audits because it will also confirm the accuracy of the dose we deliver to our patients that are treated with electron beams,” Ioannou said.

The IAEA team has developed and tested a new audit methodology for linac electron beams utilizing a specially designed holder allowing for easy and precise positioning of the dosimeters during the audit. Validation tests were performed using the IAEA Dosimetry Laboratory’s own linac facility, which went into service two years ago. The audit methodology was further verified through a multicentre pilot study in collaboration with 11 reference institutions in 10 countries.

The IAEA encourages hospitals to apply for participation in the newly launched dosimetry audit when they commission their electron beams.

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