Does radiation exposure from abdominal computed tomography increase cancer risk in patients with inflammatory bowel disease and Behçet disease?

Although high dose ionizing radiation (>100 mSv) harms humans, particularly (but not exclusively) concerning cancer, the effect of lower radiation doses is less clear.1 Low dose radiation exposure is of societal importance in relation to screening tests for cancer and occupational radiation exposure, as two examples. Inflammatory bowel disease (IBD) patients and cancer survivors undergo multiple radiological evaluations. Epidemiological data has implicated protracted exposure to a dose of 50 to 100 mSv with increased cancer risk.1 An X-ray irradiation from disease-related diagnostic procedures has recently been questioned because of the potential cancer risk associated with the increasing use of computed tomography (CT). The effective dose from plain abdominal X-ray, for example, is around 0.7 mSV, and the effective dose from abdominal CT is equivalent to the effective dose of approximately 14 to 15 abdominal X-rays.1,2 The effective radiation dose for abdominal CT is estimated to be 10 mSv and the dose for multidetector abdominal CT is 16.1 mSv.2 The number of CT scans performed has been increasing recently. Concerns arise when CT is used without a proven clinical rationale, when alternative modalities like ultrasound and magnetic resonance imaging (MRI) could be used with equal efficacy, or when CT is repeated unnecessarily. Another important issue is the increasing use of CT scans as a screening procedure in asymptomatic patients. The benefit/risk balance for CT should be considered.

Chronic inflammation of the gastrointestinal (GI) tract in Crohn’s disease and ulcerative colitis increases the risk of cancer and medications including azathiopurine, mercaptopurine, and infliximab may also increase the risk of lymphoma.3–6 Patients with Crohn’s disease have a higher cumulative radiation exposure from diagnostic imaging than patients with ulcerative colitis.7–9 About 7% to 8% of Crohn’s disease patients receive over 50 mSv every 5 to 8 years.3 Diagnosis of Crohn’s disease, surgery, prednisone use, first year of diagnosis and younger age are independent predictors of increased exposure in IBD patients.4,9 Younger patients are at greater risk for developing radiation related cancer.9

Behçet disease patients are exposed to significantly harmful doses of diagnostic radiation, especially abdominal CT. Behçet disease patients may also have an increased risk of GI malignancies because of chronic inflammation and the use of immunosuppressive agents. Use of immunosuppressants, surgery, and hospitalization carry a greater risk of increased radiation exposure in patients with Behçet disease. The impact of an additional risk factor, radiation, on the development of malignancy is likely to be greater than in healthy workers exposed to an equivalent dose. Hence, physicians should be restrictive in exposing patients with Crohn’s disease and Behçet disease to radiation-based investigations.

The first study to elucidate the cumulative radiation dose in patients with Behçet disease showed that a substantial proportion of intestinal Behçet disease patients were exposed to high doses of ionizing radiation from diagnostic tests, contrary to expectations.10 Over a mean follow-up of 7.5 years, 28.1% of intestinal Behçet disease patients received cumulative doses exceeding 50 mSv, with the mean dose being 41.3 mSv. Several other studies regarding radiation exposure from diagnostic medical imaging in Crohn’s disease reported a mean dose of 14.3 to 36.1 mSv and 7.0% to 23.7% of Crohn’s disease patients had radation exposures exceeding 50 mSv.3,5,7,8

Exposure to higher levels of ionizing radiation from diagnostic studies in Behçet disease warrants further consideration. Clinicians should consider cumulative radiation exposure dose and order the radiologic examinations only at the time of predicting the clinical impact, for example, affecting the management.

The practical issue to be considered is how to minimize radiation exposure from repeated radiation-based diagnostic examinations in these patients. Two approaches can be conceived. The first involves alternative nonradiation-based diagnostic modalities, such as MRI-based investigations and videocapsule endoscopy.11,12 Secondly, reduction of radiation exposure as much as possible is important by adjusting exposure for height and weight, using advanced technology (dual-source scanner) and techniques that reduce exposure.11