Recently, image-guided radiation therapy (IGRT) with cone-beam computed tomography (CBCT) has been used to precisely identify the location of target lesion. However, the treatment accuracy for respiratory-sensitive regions is still low, and the imaging dose is also relatively high. These issues can be solved by using the respiratory-correlated 4D IGRT with digital tomosynthesis (DT). The purpose of this study was to develop the 4D DT imaging technique for the IGRT and compare image quality between the 3D DT and 4D DT. A DT model was based on a linear accelerator (LINAC) system. In order to simulate the motion of a lesion the sphere defined in a 3D phantom was moved with an irregular pattern. Projections were separately obtained through 3 phases, which were sorted according to the position of the sphere, for simulating the 4D DT imaging. We measured profile, normalized root-mean-square error (NRMSE), noise, contrast-to-noise ratio (CNR) and figure-of-merit (FOM). Noise of 4D DT images was averagely 0.99 times lower than 3D DT images. And, NRMSEs, CNRs, and FOMs of 4D DT images were averagely 1.03, 1.22, and 4.48 times higher than those of 3D DT images, respectively. The results showed that the 4D DT imaging technique accurately determined the position of a moving target and improved image quality compared to the 3D DT imaging technique. These benefits will enable the high-precision IGRT for respiratory-sensitive regions.