Image-guided radiation therapy (IGRT) uses frequent imaging during a course of radiation treatment to verify the position of the tumor and improve the precision and accuracy of the treatment delivery. Special on-board imaging system for IGRT, most commonly cone-beam CT (CBCT), is attached to a linear accelerator. After the patient is positioned on the treatment table, images of the tumor and surrounding anatomies are taken and compared with the simulation scans. Necessary adjustments are then to more precisely target the tumor and avoid surrounding healthy tissue.