It’s astounding how much press you can get these days as soon as you start throwing around the word “radiation” and “cancer.” It seems that just by saying that something might possibly maybe perhaps increase the risk of cancer by a tiny bit you can be guaranteed massive coverage. Perhaps it’s that people just love to hate radiation or that they love to fear cancer. Maybe it’s that radiation has become associated with “big corporations” and “unnatural” medicine that should be much more “gentle.”
(and maybe I’m using too many quotes.)
It seems that finding out that diagnostic heart scans cause a tiny increase in the rate of some cancers would not be news worthy. After all, just about every procedure has some risk involved and most of these are preformed on people who are suffering from major cardiac problems, such as those who just suffered a heart attack. In such circumstances these tests undoubtedly save lives.
Never the less, this apparent tiny increase in risk has gotten tremendous press.
Heart attack survivors who undergo scans and nuclear medicine tests tend to have higher rates of cancer than those with less exposure, a new Canadian study suggests.
The researchers, from the McGill University Health Centre and the Jewish General Hospital in Montreal, note that the use of cardiac imaging tests has exploded in recent years in both Canada and the U.S.
And yet, they point out, little attention has been paid to the cumulative effect of the radiation used in those tests, or on how they might be affecting cancer rates.
So for this study, which appears in the Canadian Medical Association Journal, the researchers looked almost 83,000 patients who had a heart attack between 1996 and 2006, but who had no history of cancer.
About 77 per cent underwent at least one cardiac procedure using low-dose ionizing radiation within a year of the attack.
The tests included a heart imaging test called myocardial perfusion imaging, angiogram procedures called diagnostic cardiac catheterization and percutaneous coronary intervention, as well as a form of nuclear imaging called cardiac resting ventriculography All the tests involve exposing patients to low-dose ionizing radiation.
While most patients received only a low or moderate level of radiation, a substantial group were exposed to high levels through repeated tests — and these patients tended to be younger, healthy men.
The study’s lead author, Dr. Louise Pilote, a researcher in epidemiology, says her team found a distinct link between the cumulative exposure to low-dose ionizing radiation from cardiac imaging and the risk of cancer.
Over the course of the study, the researchers found 12,000 incidents of cancers, with two-thirds of the cancers affecting the abdomen/pelvis and chest areas.
They calculated that for every 10 “milliSieverts” of ionizing radiation, there was a 3.0 per cent increase in the risk of cancer, the study found. (A milliSievert is commonly used to measure the radiation dose in diagnostic medical procedures.)
Since the risk for cancer grows with age, the researchers accounted for that in their calculations.
“These results call into question whether our current enthusiasm for imaging and therapeutic procedures after acute myocardial infarction should be tempered,” she and her co-authors conclude.
But Pilote also cautioned that patients who need to undergo scans after a heart attack shouldn’t be dissuaded from undergoing the tests because of these findings.
“In cardiac patients who just sustained a myocardial infarction [heart attack], it’s clear that the exposure to these radiation (procedures) is warranted,” Pilote told The Canadian Press in an interview.
“And it probably way outweighs the risk of them ever developing a cancer.”
I’m sorry but I simply cannot accept the results of this study as being reliable at all. That’s not to say that it’s impossible that there isn’t a risk, there very well could be, but the study in question has a very large flaw in it. There’s really no proper control group. A proper scientific study needs to have demographic consistency between the groups being compared.
In this case, researchers looked at patients who had been treated for cardiac ailments. Some of those who were treated were given diagnostic procedures that involved ionizing radiation and some were not. The problem is that who received the radiation-based diagnostic procedures were those who doctors had greater concerns over or who had more severe cardiac conditions. These were persons who likely were in worse general health to begin with.
In general, the more severe and prolonged a person’s cardiac conditions are, the more imaging and diagnostics they will receive. A person who shows up at a hospital with a very mild heart murmur or a mild case of ventricular fibrillation is probably not going to get much in the way of diagnostic imaging of the heart. On the other hand, a person who has suffered multiple heart attacks and has a severely enlarged heart, angina and palpitations is going to receive quite a lot of diagnostic imaging.
The groups are therefore not comparable. The cardiac health of a patient is always going to be proportional to the amount of radiation they receive because worse cardiac health means more need for imaging. In all likelihood this will also mean that the patient is in worse overall health and has been under greater stress, possibly also taking more heart-related drugs and needing a variety of other procedures. They may also tend to be older, although the study claims to have compensated for this bias.
Even if this claim was true, it’s hardly newsworthy. A tiny increase in cancer risk from a lifesaving procedure does not alter the risk/reward balance by very much at all. In the case of this study the obvious bias is simply too great to even walk away with that conclusion.
…and yet it was reported like crazy anyway.
This entry was posted on Sunday, February 27th, 2011 at 10:46 pm and is filed under Bad Science, Good Science, Misc. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
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