Impact of the image quality of conebeam CT on the accelerator for the Bowtie filter / 中华放射肿瘤学杂志

ABSTRACT

Objective To estimate the impact of the image quality of conebeam CT on the accelerator for the Bowtie filter. Methods This study used the system of conebeam CT on the accelerator,and scaned the phantom of Catphan 500 in the multiplicate scanning conditions with and without the Bowtie filter. The scanning conditions were voltage120 kV, 100 kV, 80 kV, electricity25 mA, 40 mA, 64 mA,time of exposure40 MHz, collimator M20, L20, scanning angle358°. We transmitted the scanning data in the treatment planning systems of Philips Pinnacle 8. 0, and estimated the influence of the image quality.Results With and without the Bowtie filter, all of the images had high geometric precision, and the maximum difference of the nominal and actual distance at the horizontal, vertical and arrowy directions in the transection were 0. 50% and 0. 56% ( t = 0. 44, P ＞ 0. 05 ), 0. 44% and 0. 48% ( t = 1.01, P ＞ 0. 05 ),0. 50% and 0. 56% (t = 1.06,P ＞0. 05 ), respectively. The spatial resolution was 0. 167 cm, immutably.The ununiformity with the Bowtie filter was decreased of 28.0% -76.0% (t=2.53,P＜0. 05)、2.8%-50.0% (t= 3.02,P＜0.01 ) than those without the Bowtie filter, and the contrast-to-noise ratio was increased of 4.0% -41.6% (t=2.70,P＜0.05)、4.0% -50.0% (t=2.14,P＜0.05), using the collimators of M20 and L20, respectively. The Bowtie filter could display clearly the edge of scanning phantom, and improve the CT number of the image edge of phantom. And the linearity of CT number was also improved. Couclusions With the Bowtie filter, the image uniformity, the precision and linearity of CT number and the contrast-to-noise ratio were improved obviously, the edge artifacts were decreased, and the geometric precision and the spacial resolution did not change.