ABSTRACT
In current standard radiation therapy process, patient anatomy is represented by the snapshot of computed tomography (CT) images at the simulation for treatment planning. Ÿe planned radiation dose distribution, obtained from either three-dimensional (3D) conformal radiation therapy (3DCRT) or intensity-modulated radiation therapy (IMRT) can have submillimeter precision through computer-based treatment planning. Ÿe improvement in the quality assurance of the treatment delivery system, as described in Chapter 15 in this book, can also achieve similar accuracy in geometry of the collimation components and <1%–2% on the radiation output. However, patient anatomy during the the treatment course is not static; the changes can be in the orders of centimeters. Ÿese deviations in patient anatomy from the time of initial simulation to the time of treatment delivery should be minimized or accounted for, to ensure that the optimal planned dose distribution is delivered to the patient.
