A pilot study of patient-specific cardiovascular MDCT dose maps and their utility in estimating patient-specific organ and effective doses in obese patients.

BACKGROUND: Estimates of effective dose (E) for cardiovascular CT are obtained from a scanner-provided dose metric, the dose-length product (DLP), and a conversion factor. These estimates may not adequately represent the risk of a specific scan to obese adults.

OBJECTIVE: Our objective was to create dose maps sensitive to patient size and anatomy in the irradiated region from a patient's own CT images and compare measured E (EDoseMap) to doses determined from standard DLP conversion (EDLP) in obese adults.

METHODS: 21 obese patients (mean body mass index, 39 kg/m(2)) underwent CT of the pulmonary veins, thoracic aorta, or coronary arteries. DLP values were converted to E. A Monte Carlo tool was used to simulate X-ray photon interaction with virtual phantoms created from each patient's image set. Organ doses were determined from dose maps. EDoseMap was computed as a weighted sum of organ doses multiplied by tissue-weighting factors.

RESULTS: EDLP (mean ± SD, 5.7 ± 3.3 mSv) was larger than EDoseMap (3.4 ± 2.4 mSv) (difference = 2.3; P < .001).

CONCLUSION: Dose maps derived from patient CT images yielded lower effective doses than DLP conversion methods. Considering over all patient size, organ size, and tissue composition could lead to better dose metrics for obese patients.