Are Diagnostic Scans Killing You?

We came to Houston Sunday for Jim’s scans—the first since November when he was declared to be in full remission from stage IV lung cancer. The scan was to be a combined CT/PET. At least that is what we expected. But when Jim reported for the scan early Monday morning, the radiologist informed him that they would only be doing a PET—to be followed by a CT scan if anything lights up on the PET.

Obviously, the doctors are concerned about the excessive amount of cumulative radiation exposure Jim has incurred over the past nine years. I don’t have a precise number but I would be safe to say he has had 30 PET scans, 30 CT scans, 10 chest X-rays, 8 bone scans plus CT guided surgeries, and therapeutic high dose radiotherapy. It’s a wonder he is allowed to pass through airports! Initially no one thought he would live long enough to experience problems from the multitude of diagnostic tests and therapeutic procedures he has endured. But, he surprised them.

All of this got me thinking—and subsequently researching. How many scans are too many? What risks are involved? Do the benefits outweigh the risks?

Most diagnostic tests use a form of radiant energy. X-rays have been around since 1895 when Wilhelm Conrad Röntgen accidentally discovered that cathode rays penetrated many kinds of matter. He took a picture of his wife’s hand and was amazed to see the clear image of her bones. His study led to the discovery of a new kind of electromagnetic wave which he called the “X-ray.”

At about the same time, scientists in other parts of Europe were working with other forms of penetrating radiation. The implications of these discoveries for the medical field were immediately apparent. What was not immediately apparent was the risk involved with prolonged exposure. Marie Curie whose work with uranium led to the discovery of radium and polonium died of pernicious anemia—more than likely a result of repeated exposure to the radioactive materials.

The risks inherent in the chemical structure of these elements present the same problems for us in the twenty first century.

We are exposed to radiation in every day living. In fact, you might say we are showered with it. The amount depends in part on where one lives and how much sun exposure one receives. The average exposure from natural sources is thought to be between 2 and 3 mSv per year. (An mSv is a measure of radiation--the effective dose or risk averaged over the entire body.) This is an oversimplification but gives us a comparison point for the ensuing discussion of exposure from tests and procedures.

One chest X-ray is equivalent to the amount of naturally occurring radiation one would absorb over a ten 10 day period. In other words, it is negligible.

But what about a CAT scan? I was surprised to learn that the radiation from a CAT scan of the abdomen and pelvis is equivalent to five years of naturally occurring radiation. If done with contrast—ten years!

Tomorrow I will discuss the risks verses benefits of routine testing.