RESUMEN
ObjectiveTo investigate the CT number linearity of the cone-beam CT (CBCT) images at the different spatial locations in the scanning area.MethodsThe CatphanS04 phantom at the different locations are scanned repeatcdly using the CBCT on the Varian 23EX linear accelerator.The phantom is located the isocenter point,eccentric 3 cm,eccentric 6 cm,and different points on the z-axis successively on the accelerator.The scanned mode is the standard head mode.The reconstructive thickness is 2.5 cm.The different densities inserts of CTP404 module on the different locations are measured via Eclips treatment planning system (TPS) and computed by Matlab 7.0 and the CT linear fitting are then processed.In order to understand better the linear distribution along with the value of CT in the spatial distribution the results are compared with the fan-beam CT.ResultsPhantom studies show that:CBCT has good linearity performance not only under the standard header (body) of the scanning conditions,but also on such locations including the cross-sectional,the sagittal,the coronal plane and the eccentric position ( R2 ＞ 0.953 ).Bowtie filtration device does not change the CT finearity but changes the value of CT.ConclusionsThe linearity of X-ray CBCT on the Varian linear accelerator is favorable.CBCT will be used in the TPS dose calculation via further correction of the CT value.