Abstract 689: Effective Patient Radiation Doses and Skin Organ Doses at Coronary CT Angiography and Invasive Coronary Angiography
Purpose: To compare overall effective patient radiation doses and skin organ doses at coronary CT angiography (CTA) with those received at conventional invasive coronary angiography (ICA).
Methods: We obtained data for 104 consecutive patients undergoing coronary CTA on a 64-slice CT scanner (Somatom Sensation Cardiac, Siemens). The effective patient radiation dose was quantified using the Dose Length Product (DLP), which was converted into a corresponding value of effective dose equivalent using a conversion coefficient of 19 μSv/mGy-cm. The average skin organ dose was quantified using the volume Computed Tomography Dose Index (CTDIvol). We also obtained data on 102 consecutive patients who underwent diagnostic ICA on a single plane unit (Axiom Artis, Siemens). Data were obtained pertaining to a reference dose 15 cm from the isocenter that estimates the point where the x-ray beam enters the patient as well as to the number of runs, fluoroscopy time and Kerma-Area Product (KAP). Values of KAP were converted into a corresponding value of effective dose using a conversion coefficient of 180 μSv/Gy-cm2.
Results: The mean DLP value for coronary CTA was 1,120 ±200 mGy-cm with an average patient effective dose equivalent of 21 mSv. For ICA, the mean number of imaging runs was 12.2 ± 7.6 and the mean fluoroscopy imaging time was 9.9 ± 11.5 minutes. For these patients, the average KAP was 84.1 ± 83.7 Gy-cm2 with an average patient effective dose equivalent of 15 mSv. The mean CTDIvol for coronary CTA was 63 ± 7 mGy. The median CTDIvol was 58 mGy with 10th and 90th percentile values of 58 and 69 mGy, respectively. For coronary CTA examinations, the skin organ dose in patients is approximately 2.5 times higher than CTDIvol, and the average skin organ dose is thus estimated at ~150 mGy. For ICA, the average reference point dose was 1,420 ± 1,440 mGy. The median reference point dose was 960 mGy with 10th and 90th percentile values of 300 and 2,940 mGy, respectively.
Conclusion: Average effective patient radiation doses at coronary CTA are somewhat higher than those of ICA, but the latter show much more variation between patients. Average skin doses at ICA are an order of magnitude higher than those associated with coronary CTA and may exceed the threshold dose (2,000 mGy) for inducing skin damage.