The ONCORTM Expression linear accelerator is a hi-tech, multifunctional cancer therapy unit. It is a high-precision unit of which a positioning error is less than 0.5mm. It can perform the most advanced radiotherapies such as image-guided radiation therapy (IGRT), intensity-modulated radiation therapy (IMRT), thee-dimensional conformal radiation therapy (3D-CRT), four-dimensional respiration-gated radiation therapy (4D gated RT), stereotactic radiosurgery (SRS) and stereotactic body radiotherapy (SBRT) that minimize radiation to which normal tissues are exposed but focus radiation on tumor or cancer tissue. In particular, this accelerator has a built-in conbeam CT system and so can take real-time 3D-CT images to make radiotherapy more accurate. Moreover, with the built-in 160 multivane collimator, this accelerator performs special radiotherapies more accurately and more rapidly.