The WOPR and radiation risk
When I have a tough problem I usually talk it out with the Wise Old Professor of Radiology (WORP).
“WOPR,” I said,“another article came out saying that there is a risk of cancer from getting a CT scan. No one is really sure if there’s a risk, but everybody agrees that there might be. How can a family make a decision when all I can tell them is that there ‘might be’ a risk?”
“Interesting question,” said the WOPR, looking thoughtful. “Risk is as much how you feel as it is about the numbers. What is the risk of cancer from a CT scan?”
“But that’s the point WOPR; no one really knows.”
“OK, so what’s the highest risk that people think there ‘might be’”?
“The highest I’ve heard is about 1 in 4000 for one CT scan.”
“OK,” said the WOPR. “Let’s look at that. Why not say that a CT scan is 99.975% safe? Anyone would rather have a test that’s 99.975% safe than one with a 1 in 4000 risk of cancer wouldn’t they?”
“WOPR,” I said, “you can’t trick people; you have to tell them the truth.”
“Of course you can’t, and I’m not,” said the WOPR. “A 1 in 4000 risk and 99.975% safe are the same thing. If something has a risk of happening once in 4,000 times that means it won’t happen 3999 times in 4000. That’s 99.975% of the time.” (I did the math. The WOPR is right.)
“OK,” said the WOPR. “Now that I’ve got you thinking, the question isn’t risk.”
“Huh?” I said.
“Risk isn’t the question, benefit is.”
“The question isn’t what could happen that’s bad, the question is what could happen that’s good.”
The WOPR said something I won’t write down about my lack of smarts. Sometimes you have to deal with some rough edges when you ask the WOPR for advice. It’s usually worth it.
“In medicine, it’s called the benefit/risk equation, but everybody uses it all the time. It’s deciding whether or not to do something by asking if the chance of something good happening is more than the chance of something bad. And when we’re talking about risks like 1 in 4000, it’s the good that you need to be thinking about.
Let me give you an example. Would you climb a dangerous cliff to get a better view? No? Me neither. Would you climb up that same cliff to help a boy who had his foot caught? Sure you would. The risk is the same, but the benefit is different.
It’s the same thing when deciding about a CT scan. Aunt Martha says little Billy should get a CT scan when he has a tummy ache after Thanksgiving dinner because then we’d know for sure he was OK. Billy isn’t sick and the benefit is too small to take even a small risk from a CT scan. So you say no. But it’s different if Billy is sick, and the ER doctor says Billy might have appendicitis. She orders an ultrasound because it’s a good test that doesn’t use radiation, but the radiologist says she still can’t tell if Billy has appendicitis. She thinks he should have a CT scan to find out. The ER doctor agrees because if Billy has appendicitis he gets an operation and if he doesn’t he goes home. Without the CT he could get an unnecessary operation, or be sent home with appendicitis. There’s plenty of benefit and a very small risk so you say yes to the CT scan.”
The WOPR looked pleased with himself, reached into his desk drawer and took out a cigar. Trust me, the smoke from the WOPR’s cigar is something you don’t want to be around. I thanked him and left quickly.
The only thing I have to add is that it’s our job as your child’s doctors to help you to understand the benefit and the risk of the things we do. We want you to ask all the questions you have. It’s also my job as a pediatric radiologist to make even a tiny risk smaller if I can. Using the lowest dose of radiation the best equipment, and knowing what to look for are all ways we reduce the risk while maintaining the benefit when we do a CT scan.
Thanks for reading, and thanks to the WOPR.
Contributed by Dr. Alan Brody and edited by Tony Dandino, RT(MR).