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[Study of the additional filter in transcatheter hepatic arterial embolization].

It is well known that Interventional Radiology (IVR) is useful. However, the patient dose in IVR is increasing because of the prolongation of fluoroscopic time and the increase in the number of radiographies in recent years. We studied the adequacy of the additional filter for the decrease of the skin surface dose in patients with hepatocellular carcinoma of transcatheter arterial embolization (TAE). In 20 patients (15 men and 5 women, average age: 66.9 and 72.0 years old) who had undergone TAE, we estimated the skin surface dose from the records of their exposure condition (tube voltage, tube current, time, and field size of image intensifier) and the results of the phantom experiment with 2 kinds of additional filter. The estimated skin surface dose of the patient was 1.75 ± 0.84 with the additional filter of 1.5 mm thickness of aluminum (1.5 mmAl), 1.46 ± 0.67 Gy with 0.03 mm thickness tantalum (0.03 mmTa) and 1.17 ± 0.55 Gy with 0.06 mm thickness of tantalum (0.06 mmTa). Against a skin surface dose of 1.5 mmAl, the dose reduction of 16.7% was shown in 0.03 mmTa and 33.2% in 0.06 mmTa. With a DSA phantom of iodine density 0.5 and 1.0 and 2.0 mgI/ml, DSA images were acquisitioned at tube voltage 70, 80 and 90 kV to compare the detectability of contrast media in 0.06 mmTa with 1.5 mmAl. To evaluate the detectability of contrast media in 0.06 mmTa in 1.5 mmAl, receiver operating characteristic (ROC) analysis was performed with the pixel value of the phantom image. The area under the ROC curve in a 1.5 mmAl filter and the 0.06 mmTa filter provided with each contrast media density and each tube voltage was approximately a constant value. It was suggested that there was no differences in the detectability of contrast media in both additional filters. In conclusion, the skin surface dose of the patient was able to be reduced 33.2% without decreasing contrast media detectability by changing the additional filter from 1.5 mmAl to 0.06 mmTa. It was most suitable in TAE in our hospital to choose 0.06 mmTa as an additional filter.