Hello, in 2020 when my daughter was 4 1/2 years old she had an ear infection that would not go away with antibiotics, tubes and other treatments. The doctor presented an option of an “Xray” since no other diagnostic procedures were available to due Covid. He pushed to have us do the adenoidectomy but I chose the but when I got to the imaging center I found out it would be a CT of her temporal bone. I went ahead with it with little information from her doctor/the radiologist on radiation exposure. I called recently to get the dose and they said she received 55.75 mgy and the report shows DLP 420 with a note that says “pediatric reductions used.” On the phone, a radiologist from the facility she went to said “ooh, I usually turn it down” when reading the CTDI mgy which has caused me great distress the past year. My question is, should I be concerned about the amount of radiation for this one time exposure for my daughter and approximately how much MSV is this?
Thank you for your question, which we have broken down into a series of smaller questions:
What is the difference between an “x-ray” and a “CT scan”?
The term “x-ray” refers to a radiograph, a 2-dimensional picture created by passing x-rays through an object such as a body part, and capturing a stationary shadow image that shows differences in internal structures. A CT scan or CAT scan is an image obtained by passing x-rays through an object at many different angles around the object, measuring the transmission of those x-rays at every angle, and then using those measurements to create images that look like slices through the object, similar to slices from a loaf of bread.
What is CTDI?
CTDI stands for Computed Tomography Dose Index. It is a measurement of the x-ray output that was used during a CT scan. CTDI (also known as CTDIvol) is measured in milliGray or mGy. It is a dose index, not a direct measure of a patient’s radiation dose. The CTDIvol value mentioned in the dose report (55.75 mGy) is a typical value for a CT scan of the temporal bones in a pediatric patient, and is within the expected range.
What is DLP?
DLP stands for Dose Length Product. It is a calculated quantity obtained by multiplying the CTDI of a CT scan by the length of the scan in cm. The unit of measure of DLP is mGy x cm, often written as mGycm. The DLP mentioned in the dose report (420 mGycm) is typical for a pediatric patient.
What is the difference between a radiation dose reported in mGy vs a radiation dose reported in mSv?
mGy is a unit of measure of radiation dose, which is defined as the energy deposited in a sample of matter divided mass of that sample. Therefore, dose is energy (measured in Joules) per unit mass (measured in kg). 1 mGy is equal to 1 mJ/kg. mSv is the unit of measure of “effective dose”. This is a calculated value that takes into account the part of the body that was exposed to radiation. To convert a radiation dose in mGy to an effective dose in mSv requires knowing which organs were exposed. For example, a DLP of 420 mGycm for a pediatric head CT corresponds to an effective dose of about 1.7 mSv.
Should pediatric patients be imaged with the same radiation dose that would be used for an adult?
Most radiographs and CT scans are performed using automatic exposure control. This means that the amount of radiation used to form the image is automatically tailored to the body part, to use the correct amount of radiation that will create a good quality image with the least amount of radiation necessary. Using too little radiation can produce an image with inferior quality. Using too much radiation is wasteful and, in extreme cases, potentially harmful. Small children can be imaged with less radiation than adults, but larger teenagers may need adult-sized doses of radiation to produce images of adequate quality for diagnosis.
What would be a concerning level of radiation dose for an x-ray or a CT scan?
Medical imaging professionals receive extensive training in how to operate their x-ray machines and CT scanners. This training emphasizes the use of the appropriate amount of radiation to achieve the best results for the patient with the least amount of radiation. In addition, modern imaging technology includes features such as automatic exposure control that makes the job of the imaging professional easier and reduces the likelihood of errors such as incorrect radiation dose to nearly zero. The amount of radiation used in medical imaging is far below the levels that have been associated with injury or disease. Therefore, there is little need for concern about the radiation from an x-ray image or a CT scan, or even a few x-rays or CT scans. The widely accepted effective dose level above which there may be some cause for concern is 100 mSv. In medical imaging, the effective dose may reach as high as 25 mSv in rare cases, but most exams use less than a 10 mSv, and very often less than 1 mSv. The risk of harm from a single medical imaging exam (such as a CT scan) is so small that it cannot be reliably estimated.
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