Comparison of Patient Localization Accuracy Between Stereotactic X-Ray Based Setup and Cone Beam CT Based Setup on Intensity Modulated Radiation Therapy

1.1 Background and objectives Radiotherapy aims to deliver a radiation dose to the tumor which is high enough to kill all tumor cells. Daily patient localization variation, internal organ motion and deformation have long been a concern for radiotherapy. To account for these variations and to make sure adequate target coverage, margins for each direction are added around clinical target volume (CTV) to define a planning target volume (PTV). However, the larger margins may increase the irradiated volume. Nowadays, image-guided radiation therapy (IGRT) is used to accurate the patient localization and to deliver the radiation correctly under monitoring the respiratory motion. Recently, there are available several IGRT technologies such as kilovoltage (kV) and megavoltage (MV) X-ray imaging, on-board kV and MV computedtomography (CT), in-room conventional CT, and ultrasound systems. These images are most frequently used for image-guidance: positioning of the patient or target position is evaluated by a comparison of the acquired images with the planning CT or digitally reconstructed radiography (DRR) related to the planning CT. With IGRT, the dose for tumor cells is able to be escalated because that for normal tissue becomes reduced. The principle and merits of these technologies are reported by many investigators and defined in American Association of Physicists in Medicine Report. The NovalisTx (NTX), this is manufactured by BrainLAB (Heimstetten, Germany), is a dedicated to high precision radiotherapy system that offers a versatile combination of advanced technologies for treatment of tumors and other anatomical targets (Fig. 1). NTX is equipped with a 2.5 mm high-definition multi-leaf collimator and special patient localization system for precise tissue targeting (Fig. 1). The patient localization system distinguishes into 3 systems: BrainLAB 6D system, an on-board imager (OBI) based cone