Radioactive isotopes crucial in cancer diagnosis

With the possibly prolonged shutdown of Canada’s nuclear reactor at Chalk River, many hospitals and private clinics are facing a shortage of radioactive isotopes for medical imaging.

TORONTO — With the possibly prolonged shutdown of Canada’s nuclear reactor at Chalk River, many hospitals and private clinics are facing a shortage of radioactive isotopes for medical imaging.

But what will that mean for Canadian patients? And just what the heck is a medical isotope anyway?

One might imagine the substance as a tiny green glob that glows in the dark, but the reality is far less dramatic.

A radioactive isotope preparation is actually a clear, odourless liquid that is injected into a vein in the patient’s arm, similar to getting a needle for hooking up an IV or having blood drawn.

Depending on what chemical it is combined or “tagged” with, the isotope travels to a targeted area of the body, where it emits gamma rays that are picked up by a special camera.

That allows doctors to capture pictures in detail that can’t necessarily be obtained by other imaging techniques such as X-rays or CT and MRI scans.

Isotopes are also safer for patients because they involve less radiation. In fact, nuclear medicine technologists do not have to stay behind a leaded barrier while administering the tests, as they would with other imaging techniques.

“What we do in nuclear medicine is we inject radioactive isotopes to look at different processes within the body,” says Yasmin Somani, an imaging technologist at Sunnybrook Health Sciences Centre in Toronto.

“So if you are a cancer patient and we need to see if the tumours have spread to any of your bones, we can do a bone scan,” says Somani, explaining that the isotope is tagged with a phosphate compound that is attracted to bone.

“So we can actually see that phosphate being attached to bone, and if there is a disease in the bone, more of that stuff will get there and basically we’re just lighting it up.”

The radio-isotope will collect in high concentrations in areas where there is increased bone cell activity, which would occur in tumour growth, for instance.

These hot spots on the scan show whether cancer cells have spread — a vital piece of information needed for the treatment of patients, says Somani. Bone scans can also identify fractures and detect infection after a hip or knee replacement.

Medical isotopes allow doctors to peer into numerous areas of the body to see if they are functioning improperly.

Those directed at the heart, for instance, can determine if a heart attack has caused damage to the organ or whether a coronary artery may be blocked.

Isotopes can also tell doctors whether a patient’s kidneys have proper blood flow and urine output; one tagged to the gastric system can show whether the stomach is emptying correctly; another that targets the lungs can pick up a pulmonary embolism, a potentially deadly blood clot.

“There are actually a couple of different radioactive isotopes we use in nuclear medicine, but the one that’s most scarce at the moment is technetium,” says Dawn-Marie King, director of clinical operations at the University Health Network, which comprises several Toronto hospitals.

Technetium, pronounced teck-NEES-e-um, is produced from molybdenum-99, the raw isotope created by Atomic Energy of Canada in its Chalk River reactor.

Chalk River supplies about half of the world’s supply of moly-99.

Using a special generator that captures technetium from moly-99, hospital technicians produce a quantity of the isotope each morning for that day’s imaging needs.

“Because technetium only has a six-hour half-life, we can only use it for that day,” says King.

But with the Chalk River generator down for repairs, UHN and the affiliated downtown hospitals it supplies are running out of the means to make technetium. (Sunnybrook uses a different supplier.)

King says UHN has enough moly-99 for full-scale imaging only until Wednesday, then reduced amounts for Thursday and Friday.

Technicians are looking for ways to stretch the supply by cutting the amount per patient, which would mean taking longer to acquire images.

“We’re also trying to prioritize the patients that we do because there are some scans” for which there is no alternative, she says.

“Any elective patients we’re trying to book further into the future, into July, so we make sure we have enough radioactivity for the urgent patients.”

Radiologist Dr. Marc Freeman, head of nuclear medicine at UHN, said the administration is trying to tap into alternative sources of moly-99 while Chalk River is out of commission.

“The problem is a Catch-22 because everyone else, whether it be university centres or independent health centres, needs the radio-isotopes to perform the scans,” he says.

“So the bottom line is not everyone is going to be able to get their capacity and it’s going to significantly impair our function as a department.”