Estimated additional lifetime risk of cancer attributable to diagnostic CT in a pediatric bone marrow transplant cohort: Experience at a single academic institution

Purpose: To determine the frequency of CT procedures in a cohort of bone marrow transplant patients and estimate the effective dose from each CT procedure as well as rough estimates of lifetime attributable risk (LAR) of cancer (both incidence and mortality). Background: Pediatric patients who undergo bone marrow transplant benefit greatly from the diagnostic power of computed tomography, but due to the need for frequent imaging, these patients are repeatedly exposed to the carcinogenic potential of ionizing radiation. Methods: CT Imaging and patient parameters were collected from a retrospective cohort of bone marrow transplant patients. Dosimetry was estimated as a function of age, dose length product (DLP), and scan region based on published DLP to effective dose tables. Lifetime attributable risk (LAR) of cancer as a function of age, gender, and organ specific dose was derived from BEIR VII phase 2 estimates. Results: 44 patients with bone marrow transplant were included and ranged in age from 7 months to 20 years (average age, 9 years). The average number of CT studies per patient was 3.2 over the 15 month period. The average effective dose for each study was 5.9 +/– 4.5 mSv. Cumulative effective dose to each patient was 20 +/– 32 mSv. It was estimated that in this cohort, the CT imaging performed over a 15-month period on a 64-slice scanner led to a lifetime additional risk of cancer incidence of 5 in 1000 and a lifetime additional risk of cancer mortality of 2 in 1000. Conclusion: Diagnostic CT is important in the assessment and management of ill patients following bone marrow transplant. The risk of ionizing radiation leading to additional development of cancer merits using as low a CT technique as reasonable to achieve a diagnostic study.