Gordon Chan and Melanie Davidson, medical physicists at Sunnybrook Health Sciences Centre’s Odette Cancer Centre, have recently started treating cancer patients with volumetric modulated arc therapy, or VMAT.Odette Cancer Centre
Radiation to treat cancer can be life-saving. But anyone who's ever had the therapy will say the experience isn't exactly pleasant: alone on a hard bed in a darkened room for anywhere from 15 minutes to an hour, sometimes wearing an immobilization device, instructed to stay as still as possible – and to relax.
But that's set to change. New technology could make radiation a smoother process for patients, and a far more efficient procedure for radiation therapists.
Melanie Davidson and Gordon Chan, medical physicists at Sunnybrook Health Sciences Centre's Odette Cancer Centre, have recently started treating cancer patients with volumetric modulated arc therapy, or VMAT. After two years spent testing the technique on those with prostate cancer, the doctors say the advantages of the system over conventional forms of radiotherapy are dramatic.
"In VMAT's infancy, articles in the scientific literature providing evaluations of this new technique all seemed to indicate that VMAT had the potential to offer precise radiation-dose delivery in much shorter times than the current state-of-the-art modes of radiation therapy," Dr. Davidson says.
"The suggestion that VMAT seemed to consistently improve the efficiency with which we can treat patients interested us – not only because it would allow us to treat more patients, but also because it would offer a better patient experience by reducing the amount of time they were required to remain still on the bed."
Radiation therapy involves the use of high-energy radiation to shrink tumours and kill cancer cells by damaging their DNA. Like chemotherapy, it can harm healthy cells in the process. About 55 per cent of patients with cancer receive radiotherapy as part of their treatment. When a cure isn't attainable, radiation can be used to alleviate pain and improve quality of life.
In standard sessions, radiation therapists must set up a target for a dose of radiation, apply it, then stop and move to the next to location, over and over again. The radiation beam itself is fixed and its properties often have to be readjusted throughout the treatment.
"You give a shot, stop; set up to give a shot, stop; give a shot; the delivery is on and off," Dr. Davidson explains. "There's time involved in getting the beam to each location as the delivery is not continuous."
With VMAT, by contrast, the radiation beam changes its shape and intensity dynamically as the treatment machine gantry sweeps continuously around the patient. Therapists can simultaneously change three parameters as the beam rotates around the patient – the rotation speed of the gantry, the shape of the beam's aperture, and the delivery dose rate – all while taking into account the position of surrounding healthy organs and tissue.
"It delivers radiation treatment more efficiently and allows us to treat patients in a much shorter amount of time," Dr. Chan notes, adding that the technique is as accurate and safe as standard methods of radiotherapy.
It's crucial that people lie as still as possible during radiation, and faster treatment times can reduce the complexity of managing respiratory motion. It allows therapists to maximize the dose of radiation to the tumour and minimize exposure to normal cells and structures.
"We found that the increase in speed of treatment delivery did not compromise the quality of the prostate-treatment plans compared to other radiation techniques," Dr. Davidson says.
"With VMAT, prostate-cancer treatment can be trimmed to sessions lasting just two minutes, while with the other radiation treatments we offer, patients have to lie completely still, which helps to position internal organs, for seven minutes or more."
In conventional settings, though, those seven minutes can stretch out to as long as an hour with the stop-and-start method of radiation delivery.
According to Elekta, the Stockholm-based company behind VMAT, treatment times using the technology in a small planning study were up to three and a half times lower in prostate cases and between two to three and a half times lower in head-and-neck cases, compared to intensity-modulated radiation therapy, an advanced mode of high-precision radiotherapy.
Treating people faster means more patients can be seen in a single day – which translates to dramatically reduced wait times while using existing resources.
The technology seems likely to have a significant impact on the future of radiation therapy.
"This will definitely become more commonplace across the country," Dr. Chan says. "With a reduction in treatment time, everybody will want it."
Because of the success of VMAT's use in more than 50 prostate-cancer patients so far, the Odette Cancer Centre will be increasing the treatment's availability to more patients in the coming months.
"We see a real potential for VMAT in patients prescribed to receive stereotactic body radiation therapy [SBRT] in which highly focused radiation beams are used to deliver potent doses to the tumour in few treatment sessions," Dr. Davidson says. "SBRT has emerged as a treatment paradigm showing a lot of promise in treating some difficult-to-manage cancers, including some lung, liver, pancreatic, and bone tumours."
The approach could also open the door to a broader patient population, specifically those who haven't been able to have radiation in the past because of highly complex cases that made lying on a treatment bed for long periods difficult, if not impossible.
Then there's the impact on the person on the receiving end of the beam.
"It's a lot more comfortable for the patient," Dr. Davidson says. "The shorter the treatment time, the higher the patient comfort, and the lower the probability they'll move on the treatment bed. It makes it a much more pleasant experience for patient, who's likely to be stressed and anxious already."
The therapy does require more time for ongoing quality assurance of the equipment.
"Because it is a newer technique that relies on many dynamically moving parts, we've spent a lot of time validating and testing these features," Dr. Davidson says. "While VMAT is fast, we also wanted to ensure that this new treatment option was also accurate and safe.
"With so many moving bits and pieces and because of the suppressed time line, we've got to be absolutely sure that the radiation going exactly where we think it's going, and the amount that's being delivered is exactly what we think it is. It offers savings for the patient, but not so much for the physicists."