Obesity triples the radiation dose of stone protocol computerized tomography

Patients with recurrent nephrolithiasis are often evaluated and followed with computerized tomography. Obesity is a risk factor for nephrolithiasis. We evaluated the radiation dose of computerized tomography in obese and nonobese adults.

We scanned a validated, anthropomorphic male phantom according to our institutional renal stone evaluation protocol. The obese model consisted of the phantom wrapped in 2 Custom Fat Layers (CIRS, Norfolk, Virginia), which have been verified to have the same radiographic tissue density as fat. High sensitivity metal oxide semiconductor field effect transistor dosimeters were placed at 20 organ locations in the phantoms to measure organ specific radiation doses. The nonobese and obese models have an approximate body mass index of 24 and 30 kg/m(2), respectively. Three runs of renal stone protocol computerized tomography were performed on each phantom under automatic tube current modulation. Organ specific absorbed doses were measured and effective doses were calculated.

The bone marrow of each model received the highest dose and the skin received the second highest dose. The mean ± SD effective dose for the nonobese and obese models was 3.04 ± 0.34 and 10.22 ± 0.50 mSv, respectively (p <0.0001).

The effective dose of stone protocol computerized tomography in obese patients is more than threefold higher than the dose in nonobese patients using automatic tube current modulation. The implication of this finding extends beyond the urological stone population and adds to our understanding of radiation exposure from medical imaging.