Targeting cancer cells with new precision in radiation dosage raises the bar for effective treatment.
Cancer has been one of life's great mysteries, with the body turning on itself without apparent reason. It is often viewed as a disease of the modern world, but it has been found in fossil records dating back 240 million years. While it has been tough to treat and continues to spread worldwide at the rate of some 14 million new cases annually, chances of survival are increasing due to earlier detection and therapeutic advances.
Today's main cancer treatments are surgery, chemotherapy and ionizing radiation. Surgery cuts out visible tumours, while chemotherapy distributes drugs through the body that prevent the spread of the disease. Radiation sends targeted beams of intense energy to kill cancer cells, and can be used alone or in conjunction with surgery and chemotherapy. About 50% of the world's cancer cases could benefit from radiation therapy to help manage the disease.
Playing its part in the war on cancer is the Medical and Industrial Dosimetry (MID) team which is part of the National Research Council of Canada's (NRC) Metrology Research Centre. A significant focus of their research is improving how radiation doses are administered using linear accelerators (linacs)—sophisticated machines that bombard cancer cells deep in the body. Used routinely around the world, linacs must accurately dispense appropriate doses of radiation. These are calculated by medical physicists and dosimetrists in Canadian cancer centres using detectors that they send to the NRC to be calibrated against established standards. As Canada's National Metrology Institute, the NRC offers health-care and research institutions calibration services with certified traceability to internationally recognized standards.
"We provide measurement advice to Canadians, particularly medical physicists in hospitals who are responsible for dosimetry and must keep up with new technology," says Malcolm McEwen, Team Leader in MID at the NRC. "We have some form of engagement with every cancer centre across the country, as well as with universities and research organizations." Since varied systems are installed in a range of facilities and new technologies are emerging constantly, MID researchers are active in accurately characterizing new devices, developing new or existing instruments and investigating dosimetry systems. This work has led to new recommendations in international dosimetry protocols.
A dose of hope for the future
Since the first linac was used to treat a patient nearly 70 years ago, the technology has undergone continuous development. Today's state-of-the-art machines can customize radiation beams to conform to a tumour's shape and destroy cancer cells while minimizing damage to healthy tissue around them. They also contain many safety features to ensure they deliver doses as prescribed.
For example, the NRC's Elekta Synergy linac comes with an imaging system that helps operators properly position a patient on the machine and view progress throughout the treatment. "At the moment, however; we have no way of knowing if an intended dose is completely absorbed by a patient," says James Renaud, a postdoctoral fellow in the NRC's MID group. "We are looking into using the imaging technology to determine exactly how much of the prescribed radiation a patient receives, and then exploiting that information to steer the course of treatment."
Renaud explains that this type of linac has the capacity to reconstruct dose information on the spot, giving operators accurate, real-time measurements of how much radiation was absorbed. He is developing a methodology for using this important data in clinical settings so that practitioners can avoid buying additional hardware or having their busy workflows disrupted.
Raising the bar on measurement
According to Arman Sarfehnia, a medical physicist at Toronto's Sunnybrook Health Sciences Centre, the NRC plays a much larger role in the medical physics community than a national centre for measurement and calibration. "They are scientific partners with many centres and researchers, publish world-class research papers and build innovative simulation software," he says.
In 2019, when Sunnybrook acquired the next-generation Elekta Unity MR-linac, the MID team worked with Dr. Sarfehnia to calibrate doses under clinical conditions using detectors supplied by the NRC. "They sent us the detectors, we tested them in our MR-linac unit and shipped them back for readout," he says, adding that the calibrated results gave clinicians the confidence to start treating patients with the new machine. "Detectors have always been at the forefront of this kind of research. The NRC has been engaged not only in the development of new detectors, but also in the application of existing detectors to novel technologies."
Collaborations with clinical centres also benefit the NRC, since many acquire new equipment that the NRC can share. "With each machine costing millions of dollars, we cannot be buying one of each," says McEwen. "Our collaborations enable us to stay at the forefront of emerging technologies in clinical settings."
Canada has been a world leader in radiation cancer therapy since the 1950s, when the University of Saskatchewan's medical physicist Harold Johns and his graduate students became the first researchers in the world to successfully treat a cancer patient using a calibrated cobalt-60 machine, a Canadian invention and precursor to linacs. The NRC's solid foundation of excellent facilities, research pioneers and industry partnerships will continue to ensure such leadership for years to come. And that's good news for patient treatment and cure rates.