Interview with Dr. John MacKenzie: Medical Imaging and Radiation Risk in Children

Audio Interview

Hear a Patient Power interview with Dr. John MacKenzie, chief of Pediatric Radiology at UCSF Benioff Children's Hospital, who discusses the risks and protective measures in medical imaging for children.

Interview Transcript

Introduction

Andrew Schorr:

Hello and welcome to Patient Power, sponsored by UCSF Medical Center. I'm Andrew Schorr. I'm also a parent of three children, and along the way those kids have had diagnostic imaging exams. I have one child who has had a chronic GI condition, and she's been imaged several times. So parents, if you're plugged into things you see on the news, you know that there is a concern about the long-term effect of radiation on all of us but certainly on children.

We're going to explore that now with someone who is a real expert. That's Dr. John MacKenzie. He's chief of Pediatric Radiology in the Department of Radiology at UCSF Benioff Children's Hospital.

Dr. MacKenzie, thanks. Are parents asking you about radiation as their kids need imaging?

Dr. John MacKenzie:

Yes, they absolutely are. The question comes up quite often, both directly from the parents as well as the primary care physicians that care for these children.

Andrew Schorr:

I understand that the rate of imaging of children, in CT scans and fluoroscopy, X-rays and all that, and we'll differentiate different kinds of imaging as we go along, but I understand that's been going up, and that is an effort to try to understand what's going on with a health concern with a kid and maybe even spare them from a more invasive test.

Imaging in Children and Adults

Dr. John MacKenzie:

The imaging of children and adults has been increasing in this country and has been for quite some time. I wouldn't necessarily take this as a bad thing. Actually, I think it indicates how valuable medical imaging is for diagnosing as well as managing patients. It's a noninvasive test. There's no needle or surgeon's scalpel involved, and we provide our clinicians with a tremendous amount of information that's helpful in treating children.

Andrew Schorr:

So I mentioned at the outset that there was a concern that radiation might affect children differently than adults. Help us understand that.

Dr. John MacKenzie:

It comes from several lines of thinking. First, we have to understand what radiation does and what we're worried about. To answer that, it's basically radiation can cause cancer. It depends on the amount of radiation you receive, and the cells that are susceptible to cancer are those that are rapidly dividing. Certain parts of the body are more susceptible to cancer, like the gastrointestinal tract where cells are continually turning over, or in children where they're actively growing. Also children have a longer life span so they're more susceptible to accumulating additional mutations from radiation exposure we receive in the environment, and that over time later in life may predispose them to increased risk of cancer.

Andrew Schorr:

Do we have any idea what the extent of this risk is?

Dr. John MacKenzie:

That is a good question, and some people would like to think that they do. I have come to the conclusion, but I'm still open to adjusting my thinking, that we really don't know what the risk is. The reason we don't know is because the radiation doses we typically give are very low. The radiation doses that we do know cause cancer are quite a bit higher.

Because of this problem, knowing that high doses of radiation cause cancer while medical imaging with low doses of radiation may cause cancer, many people around the country and around the world have studied this problem — does low-dose radiation cause cancer. There are several different camps.

Some think that no matter what the exposure it places you at increased risk, where others feel that a little bit of radiation is actually protective. And why would that be? Well, when you're exposed to radiation your body revs up machinery that repairs DNA and repairs damage, and so if you've been exposed to a little higher levels of radiation, it may actually be a way for the body to respond to that and rev up that protective machinery.

So there are a couple different camps — those that feel that low-dose radiation does cause cancer and others who say, well, it may be even protective. I take the middle ground, just saying, well, we really don't know.

Andrew Schorr:

So given that, more imaging going on, all of us parents concerned, the debate in the radiology community about the extent of the danger or the danger at all, and you're being cautious . . . what do you do at UCSF so that kids have the proper imaging?

I understand there are alternatives. Ultrasound is not radiation, right? And MRI is not radiation. Sometimes alternative exams can be done, and then you have precautions you take when you are using X-rays, right?

Alternative Exams

Dr. John MacKenzie:

Yes, that's absolutely correct. We're doing many, many things at UCSF on many different levels, and this is true of other centers around the country as well. The first is the mantra that radiologists have adopted which is "as low as reasonably achievable," the ALARA principle. That's the acronym for as low as reasonably achievable. We try to set the dose of radiation we give as low as possible while still providing acceptable image quality to see the things we need to see inside the body.

If we step back one step further, we also ask ourselves, does the child need the test? Do they really need a CT or fluoroscopy or X-ray study that has radiation, or can we answer the clinical question differently with a different test that doesn't have radiation, such as MRI or ultrasound. So those are some of the things. If we've made a decision that, well, the best test is one with radiation, then we've set up our imaging department to image children at the lowest dose possible while still providing images that give us valuable information.

Andrew Schorr:

So that depends upon maybe what you're imaging and the sort of size and density of the kid. So a little baby, maybe needs a lot less radiation; kid who is 14, who is bigger, maybe more; the others in between, and what are you trying to look at. And I know you have lead protection for anybody who has had X-rays. So those are all precautions.

Dr. John MacKenzie:

Absolutely. For example, we've worked with our CT manufacturers and they've help us set up a color-coded system based on patient size and weight, much like when you give medications to a child, you have to adjust it based on their size and weight. We do the same thing with radiation. Those are some of the things we're doing to adjust for a smaller patient that we can see things with less radiation versus a larger one which would need more in order to produce good imaging.

Andrew Schorr:

All right. You focus on radiology for children, and you have a whole center related to that. You have technicians who are tuned in to that, but that's not always the case where someone could go. Let's give some advice to parents, whether they come to your center or wherever, and they're told their kid needs some sort of imaging. Let's go through some of the questions that you would recommend that parents could ask.

Questions Parents Should Ask

Dr. John MacKenzie:

Oh, absolutely. I think the first one that parents could ask when their physician has made the decision that their child needs an imaging study is to ask their physician if radiation is involved, and is there an alternative if radiation is involved. Then from that point, if the exam of choice does have radiation, like a CT, there are choices to be made.

A lot of people provide CT imaging in the community, and I would recommend that parents look for centers of excellence that are involved in the imaging care of children on a daily basis. There are some centers that are set up to image primarily adults, so when they get a child, it's a rare event, and they may not be as attuned to the unique imaging concerns when caring for children.

So the primary recommendation I would make is to have a discussion with their physician who is ordering the test. Then the second would be to seek out imaging centers that are involved in the imaging care of children on a daily basis.

Andrew Schorr:

Now let me ask you about that. Having been with my daughter to imaging centers, a couple questions. One is I recall vividly she had a CT. There was concern about her back, and she had a CT at a university center, but we didn't see the radiologist, and I was wondering about fertility. I don't know if I thought about cancer at that time, but fertility for a young girl, is that an issue at all?

And the other question I'd ask you just along the way is could I have asked to speak with the radiologist because often you just see the technician and you're not sure if they have the full story.

Dr. John MacKenzie:

Yes, absolutely. The radiologist is often viewed as a doctor's doctor, so we're usually interacting with the physicians who are working directly with the patients. I'm fortunate as being a pediatric radiologist that often my job takes me in contact with parents and their children, so that would be a time to ask those questions, especially during a fluoroscopy exam. A radiologist comes in and performs the exam.

The CT technologists I work with are actually very adept at answering a lot of questions, so that would be an opportunity for parents to ask at the time. If there's one the technologist can't answer, they will often call me, and then I'll talk with the parent as well. So it really is helpful to know that you can ask to talk to a radiologist if and when it is an important question.

Andrew Schorr:

And the fertility question in girls? We talked about cancer. What about imaging of their abdomen, and you worry about ovaries and all that?

Dr. John MacKenzie:

The radiation doses again are very low, so it's less a concern about fertility and more about the cancer. But then again the ovaries as well the testes in boys are areas where there are rapid turnover of cells, so we worry about a primary cancer developing in those organs. But that's usually with a much higher dose of radiation.

Andrew Schorr:

At UCSF, you see kids with long-term, sometimes very serious conditions where there may need to be imaging over time. Is that part of the discussion too, not just somebody went to the emergency room and they need to get some imaging . . . it's an accident or whatever. But maybe a kid has some kind of abdominal cancer and there needs to be imaging. Does that need to be plotted out, how often do we need to do this?

Dr. John MacKenzie:

Yes, absolutely. That's a huge concern because one or two CT scans may or may not increase the risk of cancer but when you're looking at children that have to be scanned repetitively to monitor their disease to know if the chemotherapy is working when the child is suffering from cancer, that is a concern. And we've done a number of things. We work closely with our pediatric oncologists, and they have many treatment protocols set up where imaging is a part of that treatment strategy. We're always talking about how we can minimize the number of scans, maybe scan with an even lower dose. Although the image quality may be less we're still going to see the cancer, and the child will receive less radiation.

We're also seeing a trend in these children being moved to imaging studies that don't have radiation. So ultrasound and MRI are being used more and more in place of CT for that reason, to reduce the radiation that these children receive.

The Future of Imaging

Andrew Schorr:

So that's my next question. Is thisan issue that's important in radiology and important for parents. Where are we headed in the technology and the procedures? You mentioned it now in cancer but overall, to try to do more with less, if you will.

Dr. John MacKenzie:

Sure. This is a crucial area. It's also very exciting because there are some newer developments right around the corner. But let's just talk about the nuts and bolts. I think it's a process of continual education and awareness amongst radiologists and the technologists that are running the equipment as well the larger medical community and the patients. I think with education and continued awareness we'll help tackle this area.

The other is there are some exciting technologies coming down the pike. One is MRI is getting better and better. We're able to do things with MRI that we couldn't do, like imaging faster and at higher resolution, which will help children tremendously, so fewer children will probably have a CT scan.

Then, there's new CT scan technology that is just around the corner that we may start testing at UCSF shortly where the dose received is almost 100 times less. It requires super computers to process the images and some newer technology that manufacturers are just putting the finishing touches on, but we're going to see a real change in medical imaging very shortly. I think this question about dose is hopefully going to be one of less concern because there will be less dose given for these examinations.

Andrew Schorr:

Well, this is all good news, and as a parent I think it underscores several points. First of all, if your child needs imaging you want to ask questions. And as you said, do we need to do the imaging, is there a way to do it without radiation, or if it does need radiation, can we make sure that it's the lowest possible dose for the doctors to get the information they need.

If you have a child with a chronic condition where he or she needs to be imaged over time, then it's a longer discussion about a plan that makes the most of the least radiation and least often. Then of course, can you go to a center like UCSF where, as you said, you're testing even newer technology that may have an even greater benefit.

Dr. John MacKenzie, you've covered a lot. Did we cover it all?

Dr. John MacKenzie:

Well, you know, I think there's one other important point to bring up that and that's about the risk benefit.

Andrew Schorr:

Right.

Dr. John MacKenzie:

You know, we talked about the potential risk for developing cancer with medical imaging, and my opinion, and I think some data supports it, is we just don't know what the risk is. And then the other, though, the new point I want to make is that we've been able to minimize risk in medicine in other areas by imaging children. And one example of this is for an appendicitis. Before CT was invented it was acceptable for 20 percent of children to go to the OR (operating room) and have an incision in their belly and that for the clinical diagnosis of an appendicitis, and then 20 percent of these would turn out to have a normal appendix.

Now with CT, this happens very, very rarely, so fewer children are having operations that they don't need. This is just one disease where CT has helped, so you have to think about the risk benefit.

There's maybe a slightly increased risk of cancer. I personally believe that we really don't know what that risk is. But there's also the risk associated with having an operation, going under general anesthesia that we're completely taking off the table with these exciting new imaging technologies.

Closing Comments

Andrew Schorr:

Great point. Great point. And I think this is all helping parents put it in perspective wanting the best for their child's health. Dr. John MacKenzie, chief of Pediatric Radiology at UCSF Benioff Children's Hospital, thank you so much for being with us on Patient Power.

Dr. John MacKenzie:

It was my pleasure. Thank you.

Andrew Schorr:

Well, this is what we bring you, the listener, time after time, connecting you with leading experts like Dr. MacKenzie in this program to help you get answers for yourself and in this case for your child.

I'm Andrew Schorr. Thank you for joining us. Remember, knowledge can be the best medicine of all.

Please remember the opinions expressed on Patient Power are not necessarily the views of UCSF Medical Center, its medical staff or Patient Power. Our discussions are not a substitute for seeking medical advice or care from your own doctor. That’s how you’ll get care that’s most appropriate for you.

Recorded in July 2011

 

Reviewed by health care specialists at UCSF Benioff Children's Hospital.

This information is for educational purposes only and is not intended to replace the advice of your doctor or health care provider. We encourage you to discuss with your doctor any questions or concerns you may have.

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