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Data from the Canadian Cancer Society indicates that more than a third of Canadians will develop cancer in their lifetime. Of those diagnosed, approximately 50% will be treated with ionizing radiation, either alone or in conjunction with other methods such as surgery or chemotherapy. And every cancer centre in Canada looks to the National Research Council of Canada's (NRC) Metrology Research Centre facilities for calibration of its radiation measuring equipment. Traceable calibration is part of the system that ensures that radiation therapy in Canada is delivered consistently from coast to coast to coast.
Like all other fields of medicine, radiation therapy continues to evolve, and as new therapeutic techniques are developed, new measurement standards are needed to ensure devices used to deliver radiation treatment are accurately calibrated and to provide an international system of equivalent measurements. An international system is becoming even more important because clinical trials increasingly involve numerous sites in multiple countries around the world.
For more than 20 years, the NRC has been recognized internationally as a leader in radiation calorimetry, a technique for measuring the effect of radiation's interaction with matter. When a radiation beam passes through matter, it raises its temperature, which is measured using a radiation calorimeter. In typical radiation therapy treatment, this increase in temperature is about 1 millikelvin (or one thousandth of a degree Celsius). Measuring such a small temperature rise presents a significant challenge. In projects recently carried out by the Metrology Research Centre, experts have risen to the challenge by testing specialized calorimeter devices in external facilities to address 3 new radiation therapy treatments.
TRIUMF proton therapy
The project involving this first therapy saw the Metrology Research Centre's Medical and Industrial Dosimetry team collaborate with researchers at TRIUMF, Canada's particle accelerator centre that boasts the world's largest cyclotron. Cyclotrons can be used to accelerate protons and over the last decade these devices have been installed in cancer clinics to provide proton therapy, where they have proven very effective in treating paediatric cancers. Currently, Canada does not have any proton therapy treatment facilities. However, initiatives are underway, with the first treatment centre expected to be operational in the next few years. In anticipation of this, NRC and TRIUMF researchers have joined forces on this project to develop a method to accurately calibrate proton beams.
In November 2022, a team led by Research Officer Dr. Claudiu Cojocaru carried out the first calorimeter measurements of a proton beam in Canada, at the TRIUMF facility. This work identified a method for accurate beam calibration that will benefit future clinical sites in Canada. The project involved building and then shipping a complete copy of the existing NRC primary standard system to Vancouver, rapidly assembling and commissioning it on-site and then completing an extensive series of measurements in order to establish performance metrics.
Canadian Light Source synchrotron X‑ray beam
A second project involves a new type of calorimeter for synchrotron X‑ray beams, intended to be a primary dosimetry standard for the beams at the Canadian Light Source (CLS), in Saskatoon, which produces the brightest light in Canada. Synchrotron X‑ray beams are most often used for imaging applications and material analysis, but they also have unique properties that open up the possibility for new treatment techniques not available with standard X‑ray systems. However, their dosimetry, which determines the amount or dosage of radiation absorbed by a substance, has not been well established. To fill this gap, NRC researchers from the Medical and Industrial Dosimetry team along with Carleton University doctoral student Islam El Gamal created a primary standard system for the CLS. They designed, constructed and commissioned a completely new type of calorimeter that is optimized for the CLS X‑ray beams. Testing of a prototype, completed at the end of 2022, validated simulations and established the design specifications. The next step is to develop a routine measurement workflow and compare this Canadian detector with other national standards.
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Ultra-high dose rates of radiation
A third project involves developing a primary standard for calibrating the linear accelerator beams of the third therapy, ultra-high dose rate radiation. In recent years, researchers in different countries have been investigating a potentially disruptive radiation therapy delivery called FLASH. In standard radiation treatment, the radiation is delivered over the course of 6 weeks, but with FLASH, the entire dose of radiation is delivered in less than 1 second. The result is that tumour control is maintained with normal tissue showing fewer complications. Beyond the obvious improvement in the patient experience this new treatment delivery offers, it also overcomes one of the main reasons for halting treatment with conventional radiation therapy—complications to the patient's normal tissue. That makes this new modality very attractive. However, there are significant challenges in calibrating these ultra-high dose rate beams. One solution was to develop a primary standard for calibration of a clinical beam. Research Officers Drs. Bryan Muir and James Renaud have led this effort, with the first successful demonstrations taking place at 2 cancer centres in British Columbia. The measurements create confidence in the dose delivery of FLASH radiotherapy and validate clinic-based simulation methods in support of pre-clinical research.
Collaboration is key to improve cancer therapies
These 3 projects that will improve cancer therapies speak to the excellence of the researchers and technologists at the NRC and the work they do. Team Lead in Medical and Industrial Dosimetry Dr. Malcolm McEwen says, "Combining skills in radiation physics, mechanical engineering, precision electronics, computer simulation and scientific glassblowing has allowed us to deliver specialized and optimized radiation detectors for current and emerging techniques in radiation therapy treatment. The imperative behind this effort is to ensure that Canadians receiving cancer treatment can be confident that the prescribed treatment is being delivered accurately, which leads to better outcomes."
The NRC team would like to thank the following individuals, who were critical to the success of this work: Tania Karan (BC Cancer Agency), and Drs. Cornelia Hoehr (TRIUMF), Camille Bélanger-Champagne (TRIUMF), Arash Panahifar (CLS) and Cheryl Duzenli (BC Cancer Agency).
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