An odd test and its interesting results

This past Wednesday I had my first PET scan. I’m going to describe the experience of the PET scan in a moment, but first, in an effort to understand the science behind the experience a little better, I’ve looked up some terms, and here’s what I’ve learned:  

“PET” stands for positron emission tomography.

“Positrons,” in case you didn’t know (I didn’t have this clear), are subatomic particles with the same mass and magnitude of charge as electrons, and they are the “antiparticle” of the electron. According to the online Encylopaedia Britannica, my source for all this, they “quickly react with the electrons of ordinary matter by annihilation to produce gamma radiation.” That process evidently is less dramatic than it sounds, however, since I didn’t feel any explosions during the test. Man-made radioactive sources – such as the radioactive glucose that was injected into me – produce positron emissions, and these can be measured in the PET scan. (Incidentally, I received a card explaining why I might show up for a couple of days after the scan as radioactive on Homeland Security sensors – but I guess I didn’t pass through the zone of any machine tuned to quite this level of sensitivity.)

“Tomography,” meanwhile, is defined by Merriam-Webster as “a method of producing a three-dimensional image of the internal structures of a solid object (such as the human body or the earth) by the observation and recording of the differences in the effects on the passage of waves of energy impinging on those structures.” I have to admit I’m not sure which “waves of energy” are involved here; what I understand better is that the radioactive glucose, as the Mayo Clinic explains, “collects in areas of your body that have higher levels of chemical activity, which often correspond to areas of disease. On a PET scan, these areas show up as bright spots.” Cancer shows up because cancer cells “have a higher metabolic rate than do normal cells.”

So the PET scan catches the telltale signs of cancer’s metabolic activity. It doesn’t directly measure the physical dimensions of the tumors; for that, apparently, other scans are more effective. But it does tell you how active your tumors are.

Now, the actual experience of the scan: As readers of this blog know, the MRI is an extremely noisy test – full of loud clanking noises which somehow reflect the ongoing use of the magnet that drives the “magnetic resonance imaging.” The CT (computerized tomography) scan is simpler, but even the CT scan often features breathing instructions (“hold your breath”) as the machine’s operator seeks a clear and precise image.

The PET scan has none of this. Although you lie on a narrow table and the table slides you into a donut-ring machine, all of which resembles the MRI or CT process, once you get into the machine – you’re not all the way in, apparently, but I did feel pretty enclosed – nothing happens. No clanking. No breathing instructions. Not even much movement of that table to get a focus on one part of the body or another. And nothing in particular for the patient to do; the operator encouraged me to sleep, and I think I did. About a half hour later, you’re done. Someone said it was really like magic, and I agree – something is being done that you have no perception of at all, and yet it is really happening.

What were the results so magically obtained? We learned these from the interventional radiologist an hour or two after the test was over. He confirmed that I have some areas of tumor activity – I think he found three different areas in different parts of my liver. But he also said that my other tumors, which I think include the largest tumor as well as various smaller ones, are inactive. They’re so inactive that they may be dead – which would be great – but even if they’re not dead they seem to have become inert. I’d rather they weren’t there taking up space, but my liver doesn’t seem to mind them (my liver bloodwork numbers continue to be good), and if most of my tumors have become inert, then it seems as if these years of chemotherapy have had a more profound effect than I’d realized. I thought all the tumors were still in action, just held in check by regular treatment, but it seems that most of them may have moved out of the fight.

The task ahead is to attack the ones that are still showing up as bright spots on the PET scan. We thought that the next step, the step we would discuss with the interventional radiologist, was to attack three or four particular tumors, most or all in one place, but the radiologist wants to do much more than that: he wants to attack all of the tumors that are still bright spots. That means sending Y-90 radioactive beads to multiple parts of my liver, and may mean two separate infusions of the beads.

Needless to say, it would be great to find that all of my remaining active tumors were degraded by this treatment. That may not happen, of course, but the chances of the treatment succeeding in damaging the tumors are good. That’s primarily as measured by the treatment of 15,000 -- or was it 50,000? Teresa and I heard different numbers -- colon cancer patients. (I think this is a newer technique for cholangiocarcinoma, my illness, and as always cholangiocarcinoma is such a rare cancer that the numbers of patients aren’t large.) Assuming we do hit the tumors successfully, the radiologist also expects lasting benefit as a result, rather than, say, the quick arrival of new tumors to replace the old ones.

All this is now moving pretty fast. I’m scheduled for a detailed mapping of my tumors the week after next, and for actual treatment with the Y-90 beads in early June. I’ll report on those experiences as they arrive!