Conventional Wisdom

“Curmudge, if we’re going to talk about conventional wisdom, I hope you will define it for me.”

“O course, Jaded Julie. In my view, conventional wisdom is the generally accepted knowledge about a topic at a given point in time. For example, in medieval times, the accepted way to treat an open wound was to pack it in goat dung. And until the time of Galileo, most everyone believed that the sun went around the earth once per day.”

“Wow! I’m sure glad things had changed by the time I was a child and skinned my knee.”

“Conventional wisdom can do two things; it can stagnate and become unassailable dogma, or it can evolve with the growth of knowledge. Although new knowledge in medicine seems to be slow in its adoption, we’ve seen amazing advances in our lifetime. I remain intrigued by the oft-quoted medical school professor who told entering students, ‘About half of what we teach you here will eventually be proven to be incorrect, but we don’t know which half.’ “

“What about that ‘unassailable dogma’ stuff, Curmudge? How does that come about?”

“It is easy to scare people but hard to ‘unscare’ them. When something frightens people, it is very difficult to change their view. A pertinent example is radiation. Some people fear radiation whether it’s the small amount used in medical imaging or the massive amounts confined in nuclear power plants.”

“Confess, Curmudge. Are you making this up, or do you actually know something about radiation?”

“The latter, Doubting Julie. I spent most of the summer of 1970 studying it in Oak Ridge, Tennessee. Of course, during the intervening 41 years I’ve forgotten most of what I learned. And to make matters worse, the international pooh bahs changed the names of the units of measurement. So I guess the most truthful answer to your question is that I read a lot.”

“So what did you read that catalyzed your concern about radiation and conventional wisdom?”

“Well, years ago we learned that any amount of radiation—no matter how little—had the potential of causing cancer. A plot of cancer occurrence vs. exposure, based on high levels of exposure, could be extrapolated to the origin, i.e., there was no threshold below which there was no effect. This was called the ‘linear no-threshold theory’ (LNT). It was the conventional wisdom then, and over time it became dogma and even the basis of laws and regulations. Additionally, it justified the anxiety of those who were extremely fearful of all radiation.”

“Does your reading suggest, Curmudge, that the LNT theory no longer represents the consensus regarding radiation exposure?”

“That is certainly implied in several review articles published during the past ten years. Here is a typical conclusion, ‘Based on a review of epidemiological and other data for exposure to low radiation doses and dose rates, it was found that the LNT model fails badly.’ (Vaiserman) Other authors have discussed protective effects from low radiation doses, ‘Irradiated cells protect themselves (a) by immediate defense, repair, and damage removal mechanisms and (b) by delayed and temporary protection also against renewed DNA damage, irrespective of its causes—that is, through adaptive responses.’ (Tubiana, et al.)”

“But Curmudge, there have been articles in the recent scientific and popular literature suggesting that the growing use of diagnostic computed tomography (CT) scans might increase the incidence of cancer. (Brenner & Hall, Landro) It sounds as if conventional wisdom is up for grabs.”

“It seems to be. Others have said: ‘There is no credible evidence to support the contention that current routine usage of CT scans in clinical settings in the United States will cause future cancers. Rather, the available data indicate that occasional exposure to diagnostic x-rays could possibly reduce the risk of future cancers among irradiated adults.’ (Scott et al.)”

“How do we resolve issues like this, Curmudge?”

“As you know, Jaded Julie, we’re not qualified to address that question. However, there is one more bit of older conventional wisdom that we should consider even though it contains regulations based on the LNT theory. It’s called ALARA, the acronym for As Low As Reasonably Achievable. Although the regulations might change, the concept is common sense: don’t expose anyone—patients, workers, or yourself—to more radiation than is absolutely essential. In the case of CT scans, one should be especially protective of children and pregnant women.”

“In your work long ago and for more recent diagnostic purposes you have been exposed to a variety of kinds of low-level radiation. Do those exposures leave you concerned?”

“I have always respected radiation and tried to minimize my exposures. However, for old geezers like me who won’t be around long enough to experience long-term effects—good or bad—from low-level radiation, this literature is just interesting to read and share.”

Affinity’s Kaizen Curmudgeon

Literature Cited

Vaiserman, A.M. Radiation Hormesis: Historical perspective and implications for low-dose cancer risk assessment. Dose-Response 8:172-191 (2010). http://pubget.com/paper/20585444

Tubiana, M., et al. The linear no-threshold relationship is inconsistent with radiation biologic and experimental data. Radiology 251(1):13-22 (April 2009). http://radiology.rsna.org/content/251/1/13.full.pdf

Brenner, D.J. and Hall, E.J. Computed tomography—an increasing source of radiation exposure. N. Engl. J. Med. 357: 2277-2284 (2007). http://www.nejm.org/doi/full/10.1056/NEJMra072149

Landro, Laura. Radiation risks prompt push to curb CT scans. Wall St. J. (March 2, 2010)

Scott, B.R., et al. CT scans may reduce rather than increase the risk of cancer. J. Am. Physicians & Surgeons 13(1):8-11 (Spring 2008). http://www.jpands.org/vol13no1/scott.pdf