The increased use of intensity-modulated radiation therapy (IMRT) at hospitals across Canada is maximizing the cancer-destroying capabilities of radiation treatment while minimizing its effects on healthy tissues and organs, says Dr. Adam Andronowski, a radiation oncologist at Sudbury Regional Hospital.
IMRT was conceived in 1988, but it was only in 1996 that the first linear accelerator was produced to deliver it, he said. Sunnybrook Health Sciences Centre in Toronto pioneered IMRT in Canada in 2000, and Sudbury Regional Hospital introduced the technology in 2004.
Used primarily on head and neck, prostate and central nervous system (brain) tumours, IMRT utilizes computer-controlled linear accelerators to deliver radiation doses to a malignant tumour, conforming precisely to its three-dimensional shape by modulating the intensity of the radiation beams.
Treatment is planned using 3-D computed tomography images of the patient in conjunction with computerized dose calculations to determine the dose intensity pattern that will best conform to the tumour shape.
The technique allows for higher and more effective radiation doses to be targeted at the tumour with fewer side effects, compared with conventional radiation.
The modulation of the radiation dose is made possible by small, computer-controlled motorized tungsten leaves in the head of the linear accelerator, said Andronowski. "You apply the beams from different angles - as many as six, seven or nine beams, for example, to target a tumour in the head and neck area."
The only downside of IMRT is that it's much more labour intensive, time-consuming and, therefore, more expensive than conventional radiation.
Andronowski, who specializes in treating head and neck malignancies, earned his medical degree in Poland and worked as a clinical associate in Halifax when he first came to Canada. He subsequently completed a five-year residency in radiation oncology and came to Sudbury in 2004.
"Head and neck tumours account for 60 per cent of IMRT cases in Sudbury, but represent only three per cent of all malignancies," he said.
IMRT is ideal for treating head and neck tumours because "everything happens here - swallowing, talking, reading. If you damage the muscles that control swallowing, you can't swallow. If you destroy the salivary glands, you have no taste, your teeth rot and you can't swallow because everything is dry. There are terrible side effects from conventional radiation."
IMRT is also being used more and more to treat prostate cancer because it allows radiation oncologists to deliver a higher dose to the prostate without causing damage to the bladder and rectum. One problem with the prostate is that it can move up to a half-inch in all directions depending on the contents of the bowels or bladder, making it more difficult to direct a beam with the precision required. This necessitates the use of daily ultrasound to establish the prostate's location.
Sudbury Regional Hospital participates in radiation trials through the National Cancer Institute of Canada and the Radiation Therapy Oncology Group (RTOG), a Philadelphia-based research organization dedicated to improving the survival and quality of life of cancer patients.
To qualify for participation in RTOG trials, Sudbury Regional submitted to quality assurance testing by an independent, U.S.-based quality assurance institution.
"We had to plan patients on our software and we had to deliver radiation to a phantom, an artificial body equipped with measuring devices to check how much radiation is delivered," said Andronowski. "We felt it was important to be able to participate in trials and have our planning and delivery process reviewed externally.
"If we say we're good, we're as good as we say we are, but having an external body conduct quality assurance gives us an objective stamp of approval," he said.
Seven patients at Sudbury Regional are currently participating in the National Cancer Institute of Canada's HN.6 head and neck trial that is testing the effectiveness of delivering the same dose over a shorter period of time with the addition of experimental monoclonal antibodies, as an alternative to standard IMRT with chemotherapy. Patients participating in the trial receive radiation for six, instead of seven weeks, adding somewhat to the acute side effects, but hopefully with better results.
Most hospitals administer radiation Monday to Friday for logistical reasons, "but cancer doesn't take the weekends off," said Andronowski. "Head and neck cancers grow fast and repopulate fast. Tumor cells divide every two days at first, but because of the insult from radiation, they start to divide more frequently. Instead of every two days, they divide every 1.5 days, so it doesn't make much sense to take weekends off."
To compensate for the lapse in radiation therapy during the weekend, an additional treatment is often administered one day during the week.
According to Andronowski, there are a few jurisdictions reporting good results delivering radiation daily, but "some patients wouldn't be able to tolerate it."
Andronowski complains that radiation often doesn't get the credit it deserves as an effective cancer-fighting therapy.
"People think ‘I'm getting chemo and that is going to cure me,' but radiation and surgery are more effective. Chemo is good for lymphomas, leukemia and fluid cancers. For a solid tumour, you have to either cut it out or burn it. There's a misconception about the effectiveness of chemotherapy, partly because of the role of big pharma in promoting chemotherapy drugs, said Andronowski.
Patients with head and neck cancer receiving radiation alone have a 70 per cent chance of survival. With the addition of chemotherapy, the survival rate increases to between 75 and 78 per cent, he said.
