ABSTRACT
Objective To evaluate the constancy of CT numbers of SIEMENS Sensation Open CT-simulator by analyzing the CT numbers of seven materials obtained from quality assurance(QA)tests. Methods QA tests for SIEMENS Sensation Open CT-simulator were performed with the Catphan504 phantom monthly. The CT images were obtained using three scan protocols(HeadSeq,RT_Head,and RT_Abdomen)for the CTP404 module in the phantom. The DoseLab software was used to analyze the 72 CT images acquired from January 2014 to December 2015,and the CT numbers(Y)of seven materials were obtained. Statistical analysis was performed on the Y data. The mean,standard deviation,maximum, minimum,and range values of Y for seven materials were calculated in three scan protocols. Results The standard deviation values of air,polymethylpentene,low-density polyethylene,polystyrene,acrylic acid, polyoxymethylene resin(Delrin),and polytetrafluoroethylene(Teflon)were as follows:(1)HeadSeq:0.54, 0.60,0.82,0.58,0.75,0.66,and 1.83 HU;(2)RT_Head:0.08,0.69,0.86,0.66,0.80,0.89,and 2.49 HU;(3)RT_Abdomen:0.11,0.61,0.76,0.72,0.78,0.96,and 2.56 HU.According to the statistical data, the constancy of CT numbers of the SIEMENS Sensation Open CT-simulator was in good condition in two years. Conclusions The variation of CT numbers of Teflon is the biggest among the seven materials. The relative values of CT numbers between different scan protocols vary with the relative electron density of materials.
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 : voltage :120 kV, 100 kV, 80 kV, electricity:25 mA, 40 mA, 64 mA,time of exposure :40 MHz, collimator: M20, L20, scanning angle :358°. 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.