Figure 4.

Workflow of image-guided radiotherapy (IGRT). An essential feature of IGRT is that it allows image guidance therapy through in-room images obtained during radiation delivery. Physicians can reduce target margins and spare additional normal tissue dose using 2D or 3D image guidance techniques (helical megavoltage CT (MVCT), kilovoltage cone-beam CT (CBCT), and MV CBCT), compared to in-room laser beams and skin marks. Degree of error is evaluated by comparing reference images with in-room images at every treatment time. If the error is beyond the allowable range and physicians sees a need for adaptive planning, they should retake a planning CT and restart treatment after new RT planning.