Estimating the risk of solid organ malignancy in patients undergoing routine computed tomography scans after endovascular aneurysm repair.

ABSTRACT

OBJECTIVE: Computed tomography (CT) scans are routinely used for graft surveillance in patients who have had endovascular repair (EVAR) of an abdominal aortic aneurysm. There is a growing concern for cancers associated with inadvertent use of CT scans. We report the estimated risk of radiation associated solid organ malignancy caused by routine surveillance CT after EVAR using the Biological Effects of Ionizing Radiation (BEIR VII) model created by U.S. National Institute of Science and National Research Council. METHODS: Our study estimated the excess relative risk (ERR) of a patient acquiring a solid organ malignancy secondary to radiation exposure from postoperative EVAR surveillance CT imaging. The radiation dose was calculated in sieverts (Sv). The ERR of solid organ malignancy, as given by the BEIR VII model, is = ß(s) D exp {γe*} (a/60)(η), where ß(s), γ, and η are data-derived parameters, e is age at exposure, and e* = (e-30)/10 for e < 30 and zero for e ≥ 30, a is attained age, and D is dose in sieverts. Dose-weighted ERRs were calculated to allow a comparison of malignancy risk when using a CT at all time points (model 1 0, 1, 6, 12, and 18 months, 2, 3, and 4 years, and yearly thereafter) vs replacing the CT scan with two other models (model 2 CT once in 3 years) and (model 3 CT once in 5 years). The risk was stratified by age groups, sex, and use of two different radiation doses (15 or 31 mSv) per CT scan. Statistical analysis used the paired t test. RESULTS: There were significant differences between the ERR of solid organ malignancy in those patients who would undergo surveillance CTs at all time points vs those whose surveillance consisted of alternative modalities at some time points (P < .0001). The cumulative ERR of cancer from radiation was higher in those exposed to contrast-enhanced CT scans, younger people, with highest in the group aged 50 to 55 years (ERR, 0.43), and lowest in patients aged ≥ 80 years (ERR, 0.10). CONCLUSIONS: Patients undergoing routine CT scans for postoperative surveillance after EVAR are at risk for acquiring new solid organ malignancy due to radiation exposure. The risk is higher in young patients, women, and those exposed to multiple contrast-enhanced CT scans. Our analysis questions the need for routine surveillance CT scans after EVAR in the absence of endoleaks or a change in aneurysm morphology, based on an increased malignancy risk.