Because this was basically an open tube from the hospital air to the depths of my thoracic cavity, the dressing at the top (shoulder) end had to be kept sterile. During a dressing change, the nurse who yanked up the tape sealing the hatch cover swore loudly. Then she hissed, told me not to move, and ran out of the room to find a doctor.
Doctor showed up moments later. Apparently what had happened was that the nurse felt the port tube, which features at the far (heart) end a metal needle, slip deeper into the vein. Which put my heart in immediate danger of having its hard-working smooth, aerobic muscles punctured. Which would have put me in danger of, well, dying.
Doctor yelled for the portable X-ray machine. While they set the apparatus up, I inquired about the relative risk of additional cancer induction via the radiation vs. the risk of being stabbed in the heart by the needle. The doctor looked at me funny. And explained, in the kindly and patient tone of voice reserved for those suffering from various post-traumatic stress disorders, that, yes, there is indeed a finite risk of inducing a new tumor with the radiation, but that risk was on the order of one-in-some-thousands, while the risk of being stabbed by a needle now squished down a major blood vessel to within millimeters of my heart muscle was on the order of one-in-ten.
No contest. Fire up the X-ray machine. See that, indeed, the needle has advanced dangerously close to my heart. Necessitating attendance by some sort of 24/7 on-call SWAT team who held me down, wadded me up with sterile cloths, and re-wired the port tube. The leader of the SWAT team was the only one who actually knew how to do this, but he very astutely talked one of his team members through the (intricate) process, quite successfully.
The next time we taught our risk assessment class, I used this episode as an example of comparative risk assessment. One among many examples, because, as we emphasized to the students, life itself is fundamentally an exercise in comparative risk assessment.
Let’s say you’re a shrew, and you’ve been foraging all night, and the sun’s coming up, and you have to decide whether it’s worth racing out onto the dewy lawn to rustle up one more earthworm before heading into cover for the day. The risk you run, of course, is that an owl, or an early hawk, or a weasel, or fox, or even the greenskeeper’s lawnmower, will find you out in the open. You have to balance your very real need for energy and nutrients with the equally real threat of BEING somebody else’s energy and nutrients.
Of course, we drill the students into recognizing the constant cascade of comparative risk assessment that makes up an average person’s day. Be late for class, or take the chance the campus bus won’t brake in time when we dash across the street? Trust the sterility of the processing, or skip the protein of a can of tuna? Slap together a peanut butter & jelly sandwich, or pass so you’re not exposed to the intensely carcinogenic aflatoxins? And on and on.
Radiation, of course, is a powerful source of cancer risks. Radiation damages cell components in various ways, depending on type and intensity. And certain of those cell damages yield tumorous outcomes.
And, once you’ve had cancer, your radiation dose per unit time rises enormously. In my case, over the 3+ years from my first diagnosis through my last treatment and post-treatment assessment, I had at least a dozen X-rays and, I believe, 4, possibly 5, PET scans with coincident CT scans. The PET/CT procedures are particularly interesting because there are two sources of radiation—the sugar molecules which are tagged with radioactive carbon atoms, and the X-radiation of the CT scanner.
It turns out, here in the 21st century, that we have surprisingly little quantitative information regarding the cancer risks associated with diagnostic radiation. In fact, as late as 2011 [1], an attempt to evaluate diagnostic radiation risks came with the caveat that "most of what we know about the risk of cancer for diagnostic radiation comes from an extrapolation of what happened with the atomic bomb in Japan.”
Yikes. Talk about “uncertainty” in risk balancing! Consider. To extrapolate from radiation-exposure outcomes at Hiroshima and Nagasaki, we first need to estimate the dose the dead and dying and chronically ill received. For that we have to make gross assumptions about the geographical chemistry of fission detonations more than a mile in the air at locations only generally approximated by the bomb sights [2]. We have no way to account for the vast number of parameters affecting subsequent dosimetry such as intervening structures, wind speed and direction, physical structure of the fallout, etc.
In other words, we have only the vaguest idea of what the 1945 radiation exposures were. Somewhat more subtle and credible attempts have been made to estimate risks of PET/CT procedures [3]. It is difficult to wade through the technobabble of such estimates to provide a simple summary. In general, it appears that the radiation exposure of a single PET/CT scan about equals the annual baseline or background radiation exposure for human beings. It is even more difficult to translate these exposures into estimates of cancer incidence associated specifically with the PET/CT procedures. Perhaps the best we can do is to go with the experts on this [1], and say that the likelihood of cancer attributable to PET/CT relative to cancers resulting from all sources is low but not trivial.
And, of course, the risk of excess cancers attributable to PET/CT is inversely correlated with age. Infants having such a procedure have relatively greater chances of contracting cancer than older people. Similarly, the more PET/CT procedures you have (at any age), the greater your cancer chances.
It all comes down to this. If you already HAVE cancer, or have been successfully treated for a type of cancer that is highly likely to recur, the risks of such cancer is always higher than the risk associated with the diagnostic radiation. This is similar to my SWAT team’s conclusion that the risk of being stabbed in the heart by a shiv in a major vein was greater than the risk of coming down with cancer at some later date from the diagnostic X-ray.
Finally, there is this bit of good news. Remember that risks of diagnostic radiation cancers is higher in younger patients. There are now procedures, using nano scale iron dust and magnetic resonance imagery (MRI), that can detect existing cancers as effectively as PET/CT scans [4]. This non-radiation procedure is most promising as a more benign diagnostic tool for young patients for whom radiation-based diagnostics are more dangerous.
Et voila! Problem solved! Well, sort of. There are of course the usual complications involved in bringing such an innovative tool into routine use. But it’s good to know that, at least for children, we may be able to diagnose without adding to their cancer worries.
Rock and roll, everyone. The lesson I take from my (ongoing) cancer experience? Pay attention to your comparative risks. But don’t let risk concerns hamper your quality of life. Live a rich and active life. Don’t give up ingested carcinogens (alcoholic beverages, peanut butter, barbecue), or physical carcinogens (air travel, sunlight), or crossing busy streets. Just try to balance things out so you as long as you can as well as you can. After all, you have a 100% likelihood of dying. Best to get as much good living under that constraint as possible!!!
[1] http://www.annarbor.com/health/candid-cancer-evaluating-radiation-risk-in-ct-and-pet-scans/
[2] http://inventors.about.com/od/astartinventions/a/atomic_bomb_2.htm
[3] Huang et al. 2009. http://pubs.rsna.org/doi/full/10.1148/radiol.2511081300
[4] Digitale 2014. http://med.stanford.edu/ism/2014/february/mri.html?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+NewsFromStanfordsSchoolOfMedicine+%28News+from+Stanford%27s+School+of+Medicine%29
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