Introduction

Recently, diagnostic X-ray imaging, including conventional radiography, computed tomography (CT) and nuclear medicine, have played major roles in screening, diagnosis and monitoring of treatment response in the evaluation of disease. Consequently, there has been a dramatic increase in radiation exposure: two-fold in per capita radiation dosage (from 3.6 mSv to 6.2 mSv) and six-fold in annual dosage from medical radiation (from 0.54 mSv to 3 mSv) in the United States (US) population between the early 1980s and 2006 [1,2]. Similar to rates observed in the general population, radiation exposure in injury patients who visited an emergency department (ED) has continuously increased; this rise is mainly due to the fact that CT has become one of the most important tools in the evaluation and planning for appropriate injury treatment [3,4,5].

Several studies on the cumulative effective dose (cED) of patients with a specific disease have been conducted [6,7,8]. Recently, a large-scale retrospective cohort study demonstrated an increased incidence of leukemia and brain tumors in patients who received low-dose radiation during childhood: cumulative dosages of 50 mGy and 60 mGy might triple the risk of leukemia and brain tumors, respectively [9]. However, populations in these studies included a high proportion of relatively older patients or patients who had underlying cancer or chronic disease, and as a result, the expected residual lifespan was relatively short.

In comparison with cancer or chronic disease patients, injury patients are relatively young, and can live out their natural expected lifespan if their injuries are appropriately treated. Even though multiple and repeated scans might be performed during admission, radiation exposure in injury patients has been overlooked and underestimated because of it occurring during emergent situations. Therefore, the purpose of this study was to conduct a comprehensive analysis of radiation exposure in injury patients who visited the ED of a tertiary teaching hospital according to injury mechanism, type of radiological imaging, age, and sex. We expect this analysis to present an overview of radiation exposure in injury patients and to become a basis for finding possible ways to reduce radiation dose in injury patients.

Methods

Results

Number of radiologic examinations

Of the 11,676 visits, at least one conventional radiograph was performed in 7,868 visits (67.4%), and at least one CT scan was conducted in 4,175 visits (38.5%). No radiological examination was performed in 27.6% of patients. In all, 78,025 radiologic examinations were carried out. Among these, 92.2% (6.2 per visit) were conventional radiographs, and 7.8% (0.5 per visit) were CT scans (Figure 1).

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Figure 1. Proportion of radiological examinations (n = 78,025).

CR: conventional radiography; CT: computed tomography.

https://doi.org/10.1371/journal.pone.0084870.g001

Discussion

Our results showed that, although the number of CT scans was relatively small compared to conventional radiography, most of the cED of injury patients resulted from CT. Also, traffic accident-related injury patients and fall down injury patients received relatively high radiation exposure, whereas many patients with simple lacerations, burns or animal bites did not undergo any radiological examination during their ED visit. In patients who were less than 15 years old, the most common injury mechanism was slip down injury, and most of the cED resulted from head CT scanning.

As expected, the most common injury mechanism in patients in the 0-4 years age group was slip down injury, which accounted for 46.5% (1156 of 2487 patients) of all injury mechanisms and 54.2% of the total cumulative effective dose, followed by fall down injury (13.6% of injury mechanisms, 32.3% of the total cED). This finding might be because toddlers do not walk in a stable manner, and they are frequently injured by slip downs or fall downs. Infants often fall from high locations, such as beds; therefore, fall down injuries might make up a large proportion of injury mechanisms. Furthermore, in infants and toddlers, the head is relatively larger in proportion to both weight and body length than it is in older patients; a reason why injury to the head is thought to be more common in this age group than in older patients. This trend might explain why almost all CT scans (761 of 767, 99.2%) performed in patients between 0-4 years old were head CT scans.

A previous study reported that there were differences in cED depending on trauma mechanism[15]. In that study, patients with traffic accident related injuries (motor vehicle collision, bicycle, pedestrian collision) and with fall down injuries showed higher cED than that of other patients, which was comparable with our result. In comparision to our study, patients with burn also showed high cED in the previous study. This might be because the demographics of included patients were different with only pediatric trauma patients being included in the previous study. The reason why patients with traffic accident related injuries or with fall down injuries have higher cED than other patients is probably because patients with these kind of injury mechanisms are more often severely injured than others [19,20], and diagnostic radiologic modalities might have to be more frequently performed for these severely injured patients.

Nevertheless, the first and also the most effective way to reduce radiation exposure is to avoid performing unnecessary examinations. According to an informal poll of pediatric radiologists who were surveyed during a multidisciplinary conference, organized by the Society for Pediatric Radiology, about 30% of CT examinations might not be necessary [21]. An awareness of the possible radiation hazards present during radiological examinations is essential for the risk-benefit evaluation of radiological examinations, and an education campaign for physicians and patients might be one solution to increase understanding of the possible hazards of low-level radiation [22,23]. In addition, appropriate guiding criteria that recommends when CT examinations can be justified could also reduce unnecessary scanning. In this aspect, the American College of Radiology appropriateness criteria has been shown to potentially reduce the estimated radiation dose by 44% when correctly applied [24]. Second, if a CT is performed for patient evaluation, the scanning protocol must be adjusted to the individual patient. With the advent of multidetector-row CT (MDCT), multiphase CT is frequently performed. Obtaining additional phase CT images directly increases radiation exposure, so only diagnostically beneficial phase scans should be obtained. In addition, scanning area (field of view) optimization could reduce unnecessary radiation exposure. The field of view (FOV) should be limited only to the organs or areas of interest. If a chest or abdomen evaluation is needed, omitting the thyroid or gonads from the FOV can reduce unnecessary radiation exposure on these radiosensitive organs. Third, if technically feasible, state-of-the-art dose reduction techniques, such as automatic tube current/voltage modulation, and image noise reduction with iterative reconstruction, should be applied. If these techniques can be used together, more than half of the radiation exposure can be reduced without sacrificing diagnostic accuracy [25]. Fourth, the development and use of alternative imaging modalities for injury patients (i.e., magnetic resonance image (MRI) or contrast-enhanced ultrasonography) can reduce radiation exposure. According to a recently published report, access to alternative diagnostic modalities allows for a decreased number of CTs among pediatric patients who visit the ED [26]. Fifth, clinical assessment criteria rather than a radiologic examination could present an alternative treatment or diagnosis plan. As presented in our results, performing a head CT is a major source of radiation exposure in children. According to a previous report, 70-90% of treated brain injuries are mild [27], and not all of them require CT examinations. Recently, age-specific prediction rules for identifying children at very low risk of clinically important traumatic brain injuries (and for whom CT is unnecessary) were validated with a high negative predictive value (99.95%-100%) and sensitivity (96.8%-100%) [28]. If this kind of clinical assessment model can be widely distributed, the number of CT scans and therefore the amount of radiation exposure can be reduced.

There are several limitations in our study. First, this study had a retrospective design with a single center experience. Second, other imaging studies, such as fluoroscopy and angiography, were not included in this study and the cED might be underestimated, especially in patients with severe trauma. Third, we did not evaluate the effect of CT scanning parameters in each patient, which can affect the radiation exposure during the CT scan. CT protocol optimization is also important and an effective way to reduce radiation exposure. Hence, further studies on optimizing CT protocols in injury patients should be done in the future. The last limitation is the exclusion of patients because transfers in or out of the hospital might affect the results of this study, although the number of such patients was relatively small compared to the total number of included patients.

In conclusion, most of the cED of injury patients resulted from CT, in spite of the relatively small proportion of examination numbers and the mean cED was different according to injury mechanism, age and sex. Therefore, to reduce the cED of injury patients, age-, sex- and injury mechanism-specific dose reduction strategies should be considered in more detail in the future.

Acknowledgments

The authors thank Dong-Su Jang, B,A. ( Research Assistant, Department of Anatomy, Yonsei University College of Medicine, Seoul, Korea), for his help with the figures.