By Shauna Mazenes
In what is believed to be an Ontario first, Princess Margaret Cancer Centre has used positron emission tomography (PET) technology to guide treatment in patients with meningiomas, a common type of benign brain tumour.
Unlike MRI or CT scans, PET provides images of the metabolism of the brain tumour and surrounding bone, enabling radiation oncologists to precisely target and attack tumour cells.
Dr. Derek Tsang, a radiation oncologist at the Princess Margaret, says PET scans have traditionally been used to treat patients with some chest, head-and-neck, abdominal or neuroendocrine tumours, but not brain tumours.
He advocated to Cancer Care Ontario, which now funds the procedure for some patients upon application to Ontario Health through the PET Access Program. Doctors applying through PET Access must demonstrate how the scan will change or improve patient care.
"Small meningiomas, or meningiomas after surgery, are not well seen on CTs or MRIs, which are much easier to access in terms of diagnostic tools," Dr. Tsang says. "We could be missing some of the tumour if we're not seeing all of it — especially if it's in the bone — and that's where it's the hardest to see."
PET scans, a standard nuclear medicine imaging procedure, work by injecting patients with a radiopharmaceutical substance which migrates to the part of the brain where the tumour is. The imaging scanner then lights up the targeted area, allowing radiation doctors to precisely trace out and treat the tumour.
But not all meningiomas need to be treated, according to Dr. Tsang.
Sometimes it's better to leave them alone, as long as they're not growing back, spreading or causing significant pressure on the brain, he says. In some patients, the PET scan enables radiation doctors to determine whether it's necessary to treat the tumour or not.
Christie Poirier was one of the first meningioma patients at the Princess Margaret to be treated with the procedure. She says she appreciated having PET access.
"Getting diagnosed with a brain tumour was always one of my worst fears," says Christie, whose father and uncle both passed away from brain cancer.
While meningiomas are generally considered benign, in rare cases, they can become malignant and spread throughout the brain or spine. Since Christie has a family history of this, it's imperative to control the tumour now while they can, says Dr. Tsang.
Christie agrees. "I feel more secure knowing they're doing what they can to prevent that — especially having two family members who passed away from brain cancer," she says.
The PET scan also showed a thickening in her throat, which led Dr. Tsang to refer her to a head and neck doctor to assess.
Christie says it was reassuring that doctors were able to catch something else and follow up promptly.
Dr. Patrick Veit-Haibach, Director of the PET/MR Program at UHN and Deputy Radiologist-in-Chief, says expanding access to nuclear medicine scans is invaluable for meningioma patients — especially those who have had it spread through the skull — and will inform better treatment options in the future.
"PET imaging gives radiation oncologists the opportunity to treat tumours in challenging areas where surgery is not an option anymore," he says.
"Looking ahead, we're working towards not only identifying and characterizing meningiomas with nuclear medicine scans, but also treating patients with the same molecule we use for the imaging."
