[Discrepancy between the intended isocenter and that from orthogonal linacgrams in the treatment of CT-guided stereotactic body radiotherapy(SBRT)].

Purpose: In our institution a CT scanner was installed in the same room as the linear accelerator. In stereotactic body radiotherapy (SBRT) we confirmed the isocenter position by serial thin-slice and long-scan-time CT images before every treatment as well as in planning. In planning we constructed digitally reconstructed radiography (DRR) of both the anterior and lateral views.