Trauma professionals worry about radiation exposure in our patients. A lot. There are a growing number of papers dealing with this topic in the journals every month. The risk of dying from cancer due to CT scanning is negligible compared to the risk from acute injuries in severely injured patients. However, it gets a bit fuzzier when you are looking at risk vs benefit in patients with less severe injuries. Is it possible to quantify this risk to help guide our use of CT scanning in trauma?
A nice paper from the Mayo clinic looked at their scan practices in 642 adult patients (age > 14) over a one year period. They developed dose estimates using a detailed algorithm, and combined them with data from the Biological Effects of Ionizing Radiation VII data. The risk level for injury was estimated using their trauma team activation criteria. High risk patients met their highest level activation criteria, and intermediate risk patients met their intermediate level activation criteria.
Key points in this article were:
Average radiation dose was fairly consistent across all age groups (~25mSv)
High ISS patients had a significantly higher dose
Cumulative risk of cancer death from CT radiation averaged 0.1%
This risk decreased with age. It was highest in young patients (< 20 yrs) at 0.2%, and decreased to 0.05% in the elderly (> 60 yrs)
Bottom line: Appropriate CT scan use in trauma evaluation is challenging. It’s use is widespread, and although it changes management it has not decreased trauma mortality. This paper shows that the risk of death from trauma in the elderly outweighs the risk of death from CT scan radiation. However, this gap narrows in younger patients with less serious injuries because of their very low mortality rates. Therefore, we need to focus our efforts to reduce radiation exposure on our young patients with minor injuries.
CT scan is a valuable tool for initial screening and diagnosis of trauma patients. However, more attention is being paid to radiation exposure and dosing. Besides selecting patients carefully and striving for ALARA radiation dosing (as low as reasonably achievable) by adjusting technique, what else can be done? Obviously, shielding parts of the body that do not need imaging is simple and effective. But what about simply changing body position?
One simple item to consider is arm positioning in torso scanning. There are no consistent recommendations for use in trauma scanning. Patients with arm and shoulder injuries generally keep the affected upper extremity at their side. Radiologists prefer to have the arms up if possible to reduce scatter and provide clearer imaging.
A recently published article looked at arm positioning and its effect on radiation dose. A retrospective review of 690 patients used dose information computed by the CT software and displayed on the console. Radiation exposure was estimated using this data and was stratified by arm positioning. Even though there are some issues with study design, the results were impressive.
The dose results were as follows:
Both arms up: 19.2 mSv (p<0.0000001)
Left arm up: 22.5 mSv
Right arm up: 23.5 mSv
Arms down: 24.7 mSv
Bottom line: Do everything you can to reduce radiation exposure:
Be selective with your imaging. Do you really need it?
Work with your radiologists and physicists to use techniques that reduce dose yet retain image quality
Shield everything that’s not being imaged.
Think hard about getting CT scans in children
Raise both arms up during torso scanning unless injuries preclude it.
Reference: Influence of arm positioning on radiation dose for whole body computed tomography in trauma patients. J Trauma 70(4):900-905, 2011.
The use of radiographic imaging in trauma patients has exploded over the past decade. A growing amount of research is looking at adult patients, but what about children?
Johns Hopkins did a one year retrospective review of radiographic imaging in kids age 14 and below. The studies performed and the estimated radiation dose was calculated for each child. A total of 719 children were studied and they underwent a total of 4603 studies:
CT scans – 1457 (32%)
Plain radiographs – 3097 (67%)
Fluoroscopy – 49 (1%)
CT accounted for only 32% of studies but delivered 91% of the total radiation dose. Children involved in car crashes received the highest dose of radiation (18mSv) versus burned children, who had the lowest dose (1.2 mSv). Radiation exposure increased as the injury severity increased. The average age was 8 years, which means that these children have a long time until possible side-effects emerge.
What to do? First, seriously weigh the risks and benefits of every radiographic study before you order it. If CT is not essential, do something else. The ALARA concept is key (as low as reasonably achievable):
Use weight-based CT protocols in order to deliver the minimum amount of radiation needed to get decent images
Shield all sensitive areas that are not being imaged
Use focused studies
Avoid repeat exams
Become knowledgeable about the effects of radiation exposure
Ask yourself: “What if this were my child?”
Reference: Brown, et al. Diagnostic radiation exposure in pediatric trauma patients. J Trauma 2010, ahead of print.
Okay, so you’ve seen “other people” wearing perfectly good lead aprons lifting them up to their chin during portable xrays in the trauma bay. Is that really necessary, or is it just an urban legend?
After hitting the medical radiation physics books (really light reading, I must say), I’ve finally got an answer. Let’s say that the xray is taken in the “usual fashion”:
Tube is approximately 5 feet above the xray plate
Typical chest settings of 85kVp, 2mAs, 3mm Al filtration
Xray plate is 35x43cm
The calculated exposure to the patient is 52 microGrays. Most of the radiation goes through the patient onto the plate. A very small amount reflects off their bones and the table itself. This is the scatter we worry about.
So let’s assume that the closest person to the patient is 3 feet away. Remember that radiation intensity diminishes as the square of the distance. So if the distance doubles, the intensity decreases to one fourth. By calculating the intensity of the small amount of scatter at 3 feet from the patient, we come up with a whopping 0.2 microGrays. Since most people are even further away, the dose is much, much less for them.
Let’s put it perspective now. The background radiation we are exposed to every day (from cosmic rays, brick buildings, etc) amounts to about 2400 microGrays per year. So 0.2 microGrays from chest xray scatter is less than the radiation we are exposed to naturally every hour!
The bottom line: unless you need to work out you shoulders and pecs, don’t bother to lift your lead apron every time the portable xray unit beeps. It’s a waste of time and effort!