In this population-based cohort of IBD patients, the annualized median total effective dose from diagnostic radiation was equivalent to the average dose of naturally occurring ionizing radiation received annually by the average American or European. With the greater risk of extraluminal complications that are often assessed by CT, CD patients had a median total effective dose more than twice that of UC patients. The upper quartile of patients with IBD had annualized total effective doses 2–11 times above annual natural background exposure.
Computed tomography accounted for 51% of the effective dose in our patients with CD, and 40% in UC, and practice trends demonstrate the increasing use of computed tomography (13
). While the risks of ionizing radiation at levels associated with CT imaging are extremely low (the exact value remaining a topic of debate), numerous studies have shown the usefulness of CT imaging for the evaluation of IBD patients (2
). Computed tomography has been shown to change the management of CD in 28% of patients, while computed tomography enteroclysis changed the management in 62% of patients with symptomatic CD (31
). The use of CT for the diagnosis of IBD in a pediatric population, compared to barium studies utilizing less ionizing radiation, was equally effective in 72% of patients and superior in 28%, by identifying skip lesions and better visualizing the terminal ileum (34
Over the course of our study, we observed the increasing use of CT enterography, particularly in CD patients (36
). At our institution, small bowel follow-through exams decreased by 65%, from 2,800 studies per year in 2003–2004 to 975 studies in 2007, while CT enterography increased 840% from 375 studies in 2003 to 3,166 studies in 2007 () (37
). Several studies have demonstrated superior specificity and sensitivity of CT enterography for detecting inflammatory CD compared to conventional CT and fluoroscopic exams (38
) and superior specificity compared to capsule endoscopy (CE) (40
). Recently, Higgins et al.
showed that clinical assessments correlated poorly with CT enterography findings, and CT enterography changed clinicans' perceptions of the likelihood of steroid benefit in more than 60% of patients (41
Figure 1 Small bowel imaging volumes at Mayo Clinic, Rochester from 2003 to 2007 (37). SBS = small bowel series/follow-through; CTE = computed tomography enterography.
Over the period of our study, CT enterography delivered approximately 1.5–2 times the effective dose of conventional abdominopelvic CT scanning. The radiation doses employed at CT enterography arise from the extension of acquisition parameters used from other types of CT exams using narrow slice thicknesses and requiring visualization of soft tissue attenuation differences. In our own practice, after the preliminary results of this study were known, we successfully lowered our tube current (milliampere [mA]) or increased our pitch (depending on scanner types) to reduce radiation dose by over 30%. Further reductions in radiation dose can be achieved by similar changes in CT image acquisition parameters, but even more dramatic dose reduction will likely be possible using newer image reconstruction methods or denoising algorithms applied in image space or after image reconstruction. Dose reduction is particularly important for younger patients with IBD.
Magnetic resonance imaging, US, and capsule endoscopy are alternatives to radiologic studies employing ionizing radiation. In addition to lack of ionizing radiation exposure, MR has the advantage of evaluation of stenotic lesions with MR fluoroscopy technique and conspicuity of abnormal bowel wall signal (6
). However, the benefits of CT over MR include greater availability and robustness, shorter exam times, and higher spatial resolution. At this time, MR is used as a first-line test to evaluate perianal disease, but is generally not used to evaluate small bowel disease due to long exam times, problems with patient tolerance and motion, and lack of subspecialized clinical expertise (33
). Because of its potential advantages of increased bowel wall signal and lack of ionizing radiation, MR may become the ideal modality for determining response to therapy for refractory inflammatory CD (44
In European and Canadian centers, ultrasonography is used to evaluate the thickness, stratification, and vascularity of the bowel wall to diagnose CD and UC. In their studies, the diagnostic accuracy of US was comparable to X-ray examinations, including CT (45
). Yet, widespread use of US in the United States has been limited in part due to the operator-dependent quality, inability to visualize large portions of the bowel due to bowel gas, and inability to evaluate the mesentery.
Lastly, capsule endoscopy has emerged as a relatively noninvasive method for direct evaluation of the small bowel mucosa (49
). Yet, individual study sizes have been small, and the yield of CE for the initial diagnosis of CD versus
evaluation of recurrent, known disease remains unknown. In addition, capsule retention remains a concern in patients with stricturing CD (52
The strengths of this study include the population-based inception cohort used with a broad distribution of disease subtypes and ages with significant follow-up periods (mean, 9 yr). In addition, the resources of the Rochester Epidemiology Project permitted the accurate accounting of all imaging studies obtained by the patients at the medical centers in Olmsted County, where the vast majority of health care is delivered to these patients. A final strength is the availability of accurate technique data on effective dose values from our institution's medical physics team.
However, there are some limitations of our study. First, with the resources of a large referral center and a community-based hospital, it is possible that our cohort had greater access to health care, which may either increase or decrease the number of scans a patient receives. Second, to find a median effective dose, a subset of actual exams was used, as well as known data from standard exams performed at our institution, and these values were used to represent all scans for all years in this study. With improvements in dose modulation, lower tube voltages, and changes in slice thickness, the effective doses delivered by CT have changed, and these dose reductions arc not reflected in the values estimated (19
Finally, this study was of a population-based cohort. For a referral cohort, containing patients with greater severity of illness who more often undergo repeated radiological imaging studies, one would expect total exposures of significantly higher effective doses, as suggested by the upper quartile range seen in our study.
For most patients in our cohort, annualized exposure to diagnostic radiation was not significantly greater than naturally occurring background radiation. However, for this upper quartile of patients, the degree of exposure was significantly greater, potentially increasing the risk of cancer induction. Much like gastroenterologists inform patients about the risks of biologic therapy (55
), clinicians should inform patients about potential risks of ionizing radiation (particularly those patients undergoing multiple exams), and weigh these risks against the clinical benefit in each situation (56
). Further study is needed to identify patients who require more scans and who may be at higher risk, even if only theoretical. Practice guidelines, which take into account patient age, clinical scenario, and potential benefit and risk of alternative imaging strategies, should be developed. The development of dose reduction techniques in CT, faster, more robust MR examinations, refinement of US, and the further study of the clinical usefulness of capsule endoscopy for IBD patients will decrease radiation exposure from cross-sectional small bowel imaging.
In conclusion, in this population-based IBD cohort, patients with CD were exposed to 2.46 times more diagnostic radiation than patients with UC. Overall, the annualized exposure to diagnostic ionizing radiation was equivalent to natural background radiation exposure. However, a subset of patients had substantially higher levels of exposure. Particularly in such patients, it is important to consider dose reduction techniques for CT imaging, as well as further research of imaging modalities that do not employ ionizing radiation and the development of imaging practice guidelines to limit diagnostic radiation exposure. Finally, clinicians caring for patients with IBD need to consider the radiation exposure associated with radiologic studies, particularly repeated CT scanning, and should only use these tests when the results will have an impact on the patient's management.
What Is Current Knowledge
- The average American is exposed to approximately 3.2 mSv of naturally-occurring background ionizing radiation, equivalent to 17 chest X-rays or approximately 20% of a single computed tomography of the abdomen/pelvis.
- Radiographic imaging, particularly computed tomography, provide clinically-valuable assessments of inflammatory bowel disease patients.
- Current research is beginning to elucidate the effectiveness of magnetic resonance imaging and capsule endoscopy for inflammatory bowel disease patients, representing two modalities that limit the diagnostic ionizing radiation exposure.
What Is New Here
- For comparison, median annual radiation exposure in this inflammatory bowel disease cohort is approximately equivalent to the average annual background radiation exposure in the U.S.
- Patients with Crohn's disease were exposed to 2.46 times more diagnostic ionizing radiation than patients with ulcerative colitis.
- Though risks of ionizing radiation remain unclear, the further investigation and validation of additional modalities with no ionizing radiation exposure, such as magnetic resonance imaging and capsule endoscopy, may prove particularly helpful in the subgroup of inflammatory bowel disease patients who require more frequent imaging.