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@#<b>Objective</b> To analyze the distribution features of the Bragg peak of carbon ion beams in materials using SRIM software, and to explore the use of computed tomography (CT) number to calculate the incident energy of carbon ion beams. <b>Methods</b> SRIM software was used to study the travel of carbon ion beams (100 to 300 MeV/u) in different equivalent materials, and analyze the effects of the incident energy of carbon ion beams and the type and thickness of equivalent materials on the depth of the Bragg peak of carbon ion beams. Origin 2017 was used to analyze the functional relationship between CT number and water-equivalent Bragg peak depth ratio (<i>Di</i>) through data fitting. <b>Results</b> The ratios of the Bragg peak depths in equivalent materials to that in water almost stayed constant with the increase in the incident energy of carbon ion beams. Through the functional relation between CT number and <i>D</i><sub><i>i</i></sub>, the Bragg peak depth of a carbon ion beam of a given energy in an equivalent material could be converted to the equivalent Bragg peak depth in water. <b>Conclusion</b> With the water-equivalent Bragg peak depth ratio <i>D</i><sub><i>i</i></sub> and CT number of different volume units of human tissues, the equivalent Bragg peak depth in water required for the Bragg peak to fall in the tumor can be accurately calculated, which can be used to reversely infer the needed incident energy of carbon ion beams.
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Objective This study is aimed to compare the CT number and volume of the parotid of the NPC patients between the first CT scan and the rescanning after 20 fractions.Method 14 NPC patients who had been treated were selected for analysis. Each patient was rescanned after the treatment of 20 fractions as the same protocol of the first CT sim for replanning. The CT number and volume change of the Parotid were compared and the CT number and volume change of the brain stem were also evaluated as a reference data. The results were analyzed with SPPS19, The results were analyzed with SPPS19 for t test. Results Mean right parotid CT number of the 14 patients for pre treatment and re-plan(after 20 fractions) was 6.4 and-0.5 ( =0.02) separately, the mean stand deviation was 26.5 and 35.6 ( = 0.04) separately、the mean volume was 24.6 cm3 and 16.1 cm 3 ( = 0.002) separately. Mean left parotid CT number of the 14 patients for pre treatment and re-plan was 4.4 and-1.8 ( =0.024) separately, the mean stand deviation is 29.7 and 35.5 ( =0.026) separately、the mean volume was 24.1 cm3 and 16.7 cm3 ( =0.001) separately. The Mean brain stem CT number of the 14 patients for pre-treatment and re-plan was 28.7 cm3 and 28.9 cm3 ( =0.887) separately. Conclusion After the treatment of 20 fractions , the volume of the parotid was significantly shrinked, the CT number was significantly decreased and the SD of CT number was significantly increased. The volume, CT number and SD of the Brain stem did not have significant changes. The change of the CT number could be a new observed data for the adaptive plan during the treatment as the tumor response.
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Objective To investigate the predictive value of spiral CT in composition changes of pediatric urinary.Methods A total of 25 pediatric patients with urinary stones were investigated.Eighteen patients with renal stones were stratified into two groups:an alkalization therapy alone group ( n =9 ) and a comprehensive therapy group (n =9).Flame atomic absorption spectrum (AAS) was employed to measure calcium level of the pediatric urinary stones.Spiral CT was employed to measure the peak CT number in vitro of all the pediatric urinary stones and 61 adult urinary stones,which served as controls.Results All pediatric urinary stones contained calcium ( 0.11％ - 26.30％ ).A positive correlation was observed between the CT number of pediatric urinary stone and its stone calcium level ( r =0.855,P ＜ 0.01 ).Compared to the alkalization therapy alone group,the CT number and stone calcium level of pediatricrenal stones in the comprehensive therapy group were significant higher (stone CT number:162 ± 60 HU VS.783 ±476 HU,P ＜ 0.01 ; stone calcium level:1.30 ± 1.52％ VS 19.83 ± 7.48％,P ＜ 0.01 ).Compared to ≤400 HU pediatric renal stones,＞ 400 HU renal stones contained more calcium (21.71 ± 5.27％,1.65 ±1.82％,P ＜ 0.01 ) and failed to dissolve by alkalization therapy alone ( x2 =11.455,P ＜ 0.01 ).Conclusions CT could be a predictive tool for composition changes of pediatric urinary stones.In clinical CT scanning setting,＞400 HU pediatric urinary stones probably will contain more calcium and not be suitable for alkalization therapy alone.
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PURPOSE: To compare the CT numbers on 3 cone-beam CT (CBCT) images with those on multi-detector CT (MDCT) image using CT phantom and to develop linear regressive equations using CT numbers to material density for all the CT scanner each. MATERIALS AND METHODS: Mini CT phantom comprised of five 1 inch thick cylindrical models with 1.125 inches diameter of materials with different densities (polyethylene, polystyrene, plastic water, nylon and acrylic) was used. It was scanned in 3 CBCTs (i-CAT, Alphard VEGA, Implagraphy SC) and 1 MDCT (Somatom Emotion). The images were saved as DICOM format and CT numbers were measured using OnDemand 3D. CT numbers obtained from CBCTs and MDCT images were compared and linear regression analysis was performed for the density, rho (g/cm3), as the dependent variable in terms of the CT numbers obtained from CBCTs and MDCT images. RESULTS: CT numbers on i-CAT and Implagraphy CBCT images were smaller than those on Somatom Emotion MDCT image (p<0.05). Linear relationship on a range of materials used for this study were rho=0.001H+1.07 with R2 value of 0.999 for Somatom Emotion, rho=0.002H+1.09 with R2 value of 0.991 for Alphard VEGA, rho=0.001H+1.43 with R2 value of 0.980 for i-CAT and rho=0.001H+1.30 with R2 value of 0.975 for Implagraphy. CONCLUSION: CT numbers on i-CAT and Implagraphy CBCT images were not same as those on Somatom Emotion MDCT image. The linear regressive equations to determine the density from the CT numbers with very high correlation coefficient were obtained on three CBCT and MDCT scan.
Subject(s)
Cone-Beam Computed Tomography , Linear Models , Nylons , Plastics , Polystyrenes , Tomography, X-Ray Computed , WaterABSTRACT
Objective To study the effects on tissue CT number caused by scan protocols.Methods The phantom was repeatedly scanned in different protocols by changing only one of parameters,such as X-ray tube voltage,mAs and recon kernel,while other parameters were ketp unchanged.The CT number of different materials in phantom were measured and analyzed.Results The CT numbers of tissues changed remarkably with the tube voltage and had different relativity for different tissues.The CT numbers had positive correlation with kV for such maierials as polyethyle,lexan,perspex,but for teflon the correlation was negative.The mAs and recon kernel had no effects on CT number.Conclusions The CT number of tissue changes with scanning X-ray tube voltage,so the setting of scan parameters should be taken into account in image diagnosis and radiotherapy.
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The cone-beam CT (CBCT) which is acquired using on-board imager (OBI) attached to a linear accelerator is widely used for the image guided radiation therapy. In this study, the effect of respiratory motion on the quality of CBCT image was evaluated. A phantom system was constructed in order to simulate respiratory motion. One part of the system is composed of a moving plate and a motor driving component which can control the motional cycle and motional range. The other part is solid water phantom containing a small cubic phantom (2 x 2 x 2 cm3) surrounded by air which simulate a small tumor volume in the lung air cavity. CBCT images of the phantom were acquired in 20 different cases and compared with the image in the static status. The 20 different cases are constituted with 4 different motional ranges (0.7 cm, 1.6 cm, 2.4 cm, 3.1 cm) and 5 different motional cycles (2, 3, 4, 5, 6 sec). The difference of CT number in the coronal image was evaluated as a deformation degree of image quality. The relative average pixel intensity values as a compared CT number of static CBCT image were 71.07% at 0.7 cm motional range, 48.88% at 1.6 cm motional range, 30.60% at 2.4 cm motional range, 17.38% at 3.1 cm motional range. The tumor phantom sizes which were defined as the length with different CT number compared with air were increased as the increase of motional range (2.1 cm: no motion, 2.66 cm: 0.7 cm motion, 3.06 cm: 1.6 cm motion, 3.62 cm: 2.4 cm motion, 4.04 cm: 3.1 cm motion). This study shows that respiratory motion in the region of inhomogeneous structures can degrade the image quality of CBCT and it must be considered in the process of setup error correction using CBCT images.
Subject(s)
Cone-Beam Computed Tomography , Lung , Particle Accelerators , Radiotherapy, Image-Guided , Tumor Burden , WaterABSTRACT
The CT number corresponds to electron density and its influence on dose calculation was studied. Five kinds of CT scanners were used to obtain images of electron density calibration phantom (Gammex RMI 467). Then the differences between CT numbers for each scanners were +/-2% in homogeneous medium and 9.5% in high density medium. In order to investigate the influence of CT number to dose calculation, patients' thoracic CT images were analyzed. The maximum dose difference was 0.48% for each organ. It acquired the phantom images inserted high density material in the water phantom. Comparing the doses calculated with CT images from each CT scanner, the maximum dose difference was 2.1% in 20 cm in depth. The exact density to CT number conversion according to CT scanner is required to minimize the uncertainty of dose depends on CT number. Especially the each hospital with various CT scanners has to discriminate CT numbers for each CT scanner. Moreover a periodic quality assurance is required for reproducibility of CT number.