Answer to Question #3903 Submitted to "Ask the Experts"

My female child, at four months, had a CT scan of her head to rule out central apnea. I was hoping to find out if I should begin a list of the tests she has had that expose her, and what levels she was exposed to. I had been told by the doctor that the radiation is cumulative. I'm not sure how to go about finding out exactly how much she was exposed to or what the machine was set to—would I contact the imaging center, or is there a form I need to sign? Also, are there any dangers that are associated with this test—specifically to her brain, pineal, and ovaries? When considering, in the future, whether or not to consent to similar tests, should our family history of cancers be considered? She was premature and I had been on bed rest. Shortly after she was born, I had to have a scan with radioactive dye and xenon gas for questionable DVT/thrown bloodclot. I was told to wait 24 hours to breast feed. I waited 48 and pumped. Then, a month after her head CT, I had to have a series of x rays of my back, neck, and pelvis. I requested magnetic resonance imaging (MRI) instead because of breast feeding. I didn't want to expose her to additional unnecessary radiation. I was told that although I was breast feeding, the radiation would not be present in my breast milk and go on to my baby. However, I don't understand how this could be possible, as my understanding is the radiation is absorbed by that to which it is exposed, and my mammary glands, chest, and abdomen were exposed. You see, my major concern is that although these seemingly harmless levels are being offered with each test, overall I can see the levels may be escalating or are accumulating and I need help to understand when I should ask the doctors more questions. My baby is so very small, and radiation is such a very large and daunting concept. Any response is greatly appreciated. Thank you for your time and consideration.

First, let me commend you for taking such an active interest in the medical care of your baby and yourself. Active, informed patients are an important part of successful medical care, in my opinion. Radiation exposures from diagnostic medical examinations are generally low and are almost always justified by the benefits of accurate diagnosis of possible disease conditions. There is no direct evidence of radiation ever causing any harm at the exposure levels encountered with diagnostic radiological examinations. Therapeutic uses of radiation (which you have not mentioned) naturally involve higher exposures, and physicians will consider the risks of the treatment against the potential benefits. In diagnostic uses, we have only "theoretical" models that suggest the possibility of cancer risks, but these models all extrapolate results from higher exposures to these low levels, and no one is certain about whether or not any "real" risks are involved.

That being said, first, for the CT that your daughter did have—for an adult I have from the literature estimates of around 270 mrem to bone marrow, 190 mrem to the thyroid, and an effective whole-body dose of about 180 mrem (ICRP Publication 62). Exposure settings are usually set lower for children and smaller adults. I cannot give an exact dose estimate; only the people at the medical center could, if they have made such measurements on their specific machine using the settings that were used for the examination. The numbers above are probably reasonable to use, with some downward adjustment for the fact that this was a study done on a child. By comparison, all of us receive about 300 mrem of radiation from natural background radiation every year.

Second, for the examinations that you received, we have to make a distinction here between RADIOACTIVITY and RADIATION. Radioactive material was involved in your deep vein thrombosis (DVT) study. Radioactive material gives off radiation. If your breastfeeding child swallowed some of the radioactive material given to you that may have passed into your breast milk, she could have received a radiation exposure, yes. It sounds like you received good advice on the breast milk feeding interruption. If you received further x rays or CTs, these involve only radiation produced by machines (without any radioactive material involved, the machine simply produces radiation by a mechanical means), and no radiation could later pass to your child. As soon as the machine is disengaged, all radiation is dissipated. Further, it sounds like you opted for an MRI exam. It does not even produce any ionizing-type radiation, which we have been discussing so far (see the Ask the Experts area on Radiation Basics for more terms and definitions). The same principle of machine-produced radiation applies, and the type of radiation is called nonionizing, which means that it does not have the potential to do direct damage to cells of the body that ionizing radiation does. So, for a number of reasons, there is really no concern here for the child.

In summary, I think the concerns for any health effects at all in your child are very low. Talk with your physician about the tests your child has had so far if she orders further tests involving radiation for your child, but trust her if she thinks that the tests are indicated. The exposures are usually comparable to those that we receive routinely from natural radiation all around us, and the benefits of the medical exams are of course very significant.

Michael G. Stabin, PhD, CHP