Killers Within

What if you could spot cancer before it was too late?

Avis Picton

From the March 2002 issue of BC Business Magazine

What if you could find tumors before they had become big and bad enough to kill you?

Well, now you have a fighting chance with this latest technological gizmo: the PET scanner

What's the scoop?
The procedure's formal name is Positron Emission Tomography, PET for short. The first total-body PET scanner in Canada for private-pay clinical use by cancer patients became available in October 2000 in Vancouver. It's a Siemens ECAT EXACT 47, manufactured in a suburb of Chicago.

Does it scan pets?
No, although it's probably technically possible (sort of like CAT scanners and cats).

What does it do then?
The PET scanner demonstrates 'function', as opposed to the more familiar CAT and MRI scans which show 'structure'. This can be particularly beneficial in cases where normal anatomy has been distorted by surgery or radiation, making physical features difficult to recognize.

It is especially useful in determining location and extent or spread of cancer, as well as planning/monitoring treatment for cancers of the lung, colon/rectum, breast, head and neck, as well as lymphoma and melanoma. It is also helpful in some cases of ovarian, pancreatic and thyroid cancers.

PET scans are also used with cardiology patients (especially to determine who should have bypass surgery versus heart transplantation) and in neurology, where they have been in use since the 1980s.

Where can I get one in Vancouver?
So far, only at the Vancouver PETScan Centre operated by International PET Diagnostics in the BC Research & Innovation Complex at the UBC. Email: info@petscan.ca.

How does it work?
The PET scan exploits cancer's voracious appetite for glucose. The patient receives an injection of a small amount of radioactive compound fluordeoxyglucose (FDG), similar to glucose but with the addition of a radioactive fluorine atom, which malignant cells take up more avidly than normal cells. Once uptake is complete, the FDG is trapped within the cells, allowing time for imaging.

(Skip this paragraph if the equation E=mc2 makes you think of a rap artist rather than Einstein.) When the radioactive fluorine portion of an FDG molecule decays to its ground state, it emits a positron, the anti-matter equivalent of an electron. It then collides with an orbital electron, and as will happen when matter meets its corresponding anti-matter, both are annihilated and their rest mass energy converted to gamma radiation.

Simple, eh? In any case, the end result is two 511KeV photons, running away from each other in opposite directions at the speed of light (well, maybe not quite that fast, since the scan doesn't take place in a vacuum.) Photons traveling in this manner are identified by the specialized detection present in a full ring dedicated PET scanner. Sophisticated electronics convert the photon energy into electronic signals, which a computer uses to reconstruct a 3-D image of the body's glucose metabolism.

Who invented it?
UCLA medical scientist Michael E. Phelps (no relation to the Westcoast Energy honcho as far as we know) is generally credited with the invention. The first machine was developed in the U.S. in 1973.

Can I buy one?
Not likely. While the scanner itself is pricey enough at $2 million, the cyclotron unit needed to manufacture the radioactive compound will run you more like $4 million, with operating costs of about $1.5 million a year. The Vancouver scanner currently obtains its radioactive material from Seattle.

How do you get one?
You must be referred by a doctor. Most often this will be a cancer specialist. A date with the scanner normally takes a few weeks.

How much does a scan cost?
$2,500. The B.C. Medical Plan does not cover the test. The only province which fully covers PET is Quebec, with limited coverage available in Ontario and Alberta.

The cost of a PET scan paid for by an individual is eligible for the medical tax credit. The disability tax credit or the attendant care expense deduction may also be available. After that it gets fancy. Employees enrolled in group benefit programs may be able to have a PET scan paid for by the insurance carrier on an 'extra-contractual' basis (the expense is a tax deduction for the employer).
Business owners, whether sole proprietorship, partnership or corporation, can, if they do it properly, use company money to pay for their own PET scans. (The cost is tax deductible to the business and is not a taxable employee benefit.) Group insurance plans may cover the scan as an extra-contractual benefit, or, for businesses without group insurance, a Private Health Services Plan (PHSP) can be set up for this purpose.

(Consult with a tax or financial advisor for details on any of the above.)

Is it safe?
There are no known side effects. The radiation exposure involved is less than that received from many CAT scan procedures. According to Dr. Worsley, it is equivalent to the background environmental radiation a person receives just by living in Vancouver for five years.

Who shouldn't have it?
Like any test involving radiation, pregnant or breast-feeding women shouldn't undergo PET scanning. There can be technical difficulties with diabetic patients, as high levels of blood glucose will crowd out the FDG from the tumor cells.

Is it a big deal?
Not compared to a lot of tests. No strenuous exercise, long walks or heavy lifting from 24 hours before the scan; exertion stimulates the uptake of glucose by muscle tissue. You're allowed a light meal without sugar and caffeine six hours before the appointment, but only water after that. You're also 'encouraged' to bring a small snack to eat after the procedure (geez, for $2,500 couldn't they throw in a sandwich?).

You check in, sign a consent form and fill out a medical history sheet. No need for a bottom-baring gown - you get to wear your own comfy clothes. Things start off with a finger prick blood sugar test. The FDG tracer is injected intravenously, and you relax in a reclining chair for half-an-hour or so while the FDG circulates. Next, a bathroom break to eliminate excess FDG from your bladder. Finally you lie on a bed that passes through the PET scanner for another 45 minutes or so. The computer and the interpreting physicians do the rest of the work while you eat your snack and drive home. The faxed results reach your doctor by 2 p.m. the next day; hard copies of the results, and the images, follow within 48 hours.

Are they foolproof?
No. Due to the low metabolic activity of very small tumors or tumors that are in the process of breaking down, the scanner may miss them. As well, false positive results may occur in the presence of active inflammation or infection, since white blood cells that mediate the inflammatory process take up glucose at a high rate.

Dr. Avis Picton is a family practitioner in Delta as well as a freelance writer.