By Nick Obradovich
Recently, Donald Frush, M.D., professor of radiology at the Duke University School of Medicine, chief of pediatric radiology at Duke Children’s Hospital and Health Center and a leading pediatric radiation dose expert, sat down with ITN to discuss the current efforts being made to lower the radiation dose for pediatric CT scans.
Q: What are the unique challenges with imaging children in terms of radiation dose?
A: You might be able to divide these up into a couple of categories. Pediatrics differ from adult medicine in a variety of ways. One of the ways is that the patient population, especially when they are younger, is not going to provide same kind of history and information that an adult would be able to provide. A lot of times the care is based on observation, is based on preliminary laboratory values, temperature and so forth, but the clinical history is often age dependent based on what the patents might observe. Getting individual studies is made more complex and the threshold may change. It may be lower because you’re not able to garner the same kind of information you get with an adult.
I think, oftentimes, children are cared for by people who feel much more comfortable dealing with adults and so there anxiety level about doing something or missing something ends up being a little bit higher and that may alter the threshold to obtain imaging studies. They may be less familiar with pediatric diseases, as well, so ordering studies may be more frequent in children versus an analogous situation with adults that a care provider feels more comfortable observing rather than ordering a study.
When the study is done, it’s important to tend to radiation dose issues. First of all, the kids don’t need as much dose to get diagnostic image quality as an adult. You can’t use the same settings in kids as you do adults because it will provide a higher dose to that child than an adult actually gets. If you scan an adult in x dose setting, and a child an x dose setting, they’re going to get more dose than an adult does for a variety of reasons. The kids are more sensitive to radiation. That is partly age-dependent and decreases somewhat as they older. The rough number quoted is going to be two to three times more sensitive to radiation in terms of biological effects than adults. Some people quote a number as high at 10 times, and I think that’s probably an extreme.
You have to realize with kids is that they might be getting a CT scan or two when they are five-years-old for some medical condition. One or two CT exams isn’t really going to make significant difference in terms of developing cancer, but you don’t know what that child is going to be need at age 10, 15, 20 or 30. They may develop kidney stones and get five or 10 CTs. They have this cumulative possibility that someone who is 75 or 80 isn’t. You are probably not going to be CT scanning an eighty-year-old for the next 20 years, but with someone who is five, you are talking about 70 to 75 years of potential scanning.
Those are all reasons why CT scanning in children ends up being a different bird than that of adults.
Q: What inspired you to create the color-coded pediatric protocols on CT scanners?
A: From a general sense, it was trying to find a way that protocols could be easily designed to have size-appropriate techniques for children. That’s what technologists and radiologists want. They want to have size-appropriate protocols. Many of the previous protocols were based on age. Age is only a rough indicator of size. You can have a 20kg one-year-old, you can a 20kg four-year-old…depending on height, the techniques may need to be different for those. You can have the same weight for someone one or four and the techniques may need to be similar. If you’re basing it on age, you may provide more radiation for a four-year-old that is skinny and short than someone who is overweight and tall. It makes more sense to have size-based protocols than age-based.
This color-coded system had been in used in the emergency setting for a number of years, and simply pre-calculated interventions where there was fluid or medications, based on the length or the weight of the child in emergency care. We elected to use the same color zone and size that had already been validated in those kids getting medications for CT protocols. It also made sense because we weren’t developing two different systems in the hospital. That is, if they have a color-coded category, they are assigned “blue” in the emergency room, that way we know they are going to be getting a “blue” body CT scan. There is some efficiency and decreased chance for doing the wrong kind of study on a child if we use the same system in the emergency room and radiology.
Q: Are there any types of CT scans that the radiation dose is particularly high for pediatric patients?
A: There is a very complicated answer to that. It’s probably best to treat all CTs the same, which is to be sure that you are using the necessary amounts of radiation to achieve the diagnostic information that you need. It’s important to decide that the CT is necessary. That’s the first step.
The major dose issues are going to be found when people do multi-phased scanning, pre- and post-contrast, arterial phase/venous phase or venous phase/delayed images. When you do more than one phase for a child that is going to increase the radiation dose and will usually increase in multiples of the number of phases you are doing if you don’t make any adjustments in the technique. Generally, there are very few situations where multi-phased scans are necessary in kids. That is a scan that I think is overused in children, pre- and post-contrast, in particular.
Repeat scans — get a scan, then another scan, then another scan, in a setting of renal stones or something. People have to realize that dose is cumulative. Sometimes patients go to different places or move…they may have gotten two CT scans in Boston, and now they are moving down to Atlanta and got two more. Boston doesn’t know that Atlanta did two more, and Atlanta doesn’t know that Boston did two. The parents may not remember that the kid has had four scans, but the fact is they’ve had four scans. Getting multiple scans is something people need to be cognizant of too. I think the way to address that, in the end, is some sort of dose record which commutes with that patient wherever they go, like a vaccine record. There are people working on that, but it’s far from a nationalized system.
Some regions of the body are more radiosensitive than others. If you are doing a CT scan of the foot, the dose ends up minimal to that part of the body. If you are talking about radiation in the chest (lungs, breast), thyroid, abdomen (liver, spine, intestines), those tend to be radiation-sensitive areas versus the extremities. I don’t want anyone to get the idea that they can scan the extremities as much as they want, because that is not the right thought process. Those areas (chest, abdomen, pelvic) have more tissues with a higher weighing factor in terms of risk of developing cancer.
Q: How much is understood about the risks of low-level radiation?
A: It depends on whom you are talking to. Physicians in the past five or 10 years are certainly more aware of the dose delivered by CT and the mechanisms to manage that dose. Radiologists, technologists, physicists are all more aware. I believe that awareness is slow but increasing in clinical colleagues…those people who order studies such as surgeons, emergency room physicians, pediatricians, internists, cardiologists…the awareness is increasing. It’s not there yet, as there is more education that needs to ensue, but it is better than it was.
Q: Are they any new features in developing on CT scanners that could further lower the dose for pediatric patients?
A: Some of the things in the works are better dose estimates for children. Right now, the ones available are geared for adults, so in terms of estimating or indexing the dose that the kids get on the scanner, it’s very problematic. There are some organizations, particularly The Alliance for Radiation Safety in Pediatric Imaging, that are working with groups including AAPM and other groups, to get better dose representation. That doesn’t necessarily decrease the dose in and of itself, but may make a better representation where people can actually use that as a quality measure. This is going to take a few years to do.
I would like to see a universal language among all the vendors in terms of the representation of dose on the exam that isn’t buried somewhere in DICOM information, about what the dose is; that there is something that conveys with an examination some representation of dose that is easily understood. What that language should be is something in the works.
I would also like the manufacturers to work towards having protocols or warnings or comments that if you put in a protocol that falls outside of a guideline range, a manual override would need to be made before the scan started. Right now you can do whatever you want and get whatever exam you want. This is not in the works right now. This will take some consensus by the manufacturers.
The companies are invested in designing better application training. Helping the individual users work their new scanners or technologies would be beneficial (by providing videos, etc.) This is something that came out of a vendors’ conference in August. The companies agreed to provide educational opportunities for training when new scanners where installed. I think that effort is going to have a tremendous impact on having people use the right protocols for children.
Q: Having a dose record sounds like another good reason to call for wider adoption of EMRs. Is there a specific dose record section in your EMR?
A: No, there is not. You raise a good point in that it would be helpful thing to do. These electronic systems, most of them, don’t talk to each other. Somebody will need to push for a national standard. It may take a company like Liberty Mutual or Blue Cross saying “we’re going to do this across the country for all our patients,” then other people may follow.
Right now [for dose records], parents have a card that they keep like their vaccine records to archive the exams their child has had. In terms of an electronic record, it’s going to take a commitment from someone to do that. The VA probably can, but that’s not the right population. We need to have this pushed from a national level, which is why my thought is if you have a major third-party payer pick this up and design it, that would be a start. Whether that system is what we’re using is 20 years isn’t as important as provoking others to do this and having a national dialogue. Right now [dose records] are just on a hard copy level.