Traditionally, the physician needs to increase safety margin around the tumor for conventional radiation therapy to ensure the radiation is still within the tumor area, thus we cannot effectively spare normal tissue organ. These limitations were mainly due to patient setup uncertainties and internal organ motion. Image guided radiation therapy (IGRT) provides high-resolution, two dimensional imaging and three-dimensional volumetric images prior to treatment to pinpoint bony landmark or internal markers to ensure the treatment accuracy and targeted to the same position on every treatment session. Further, minimize the deviation of internal organ motion or patient setup uncertainties, and decrease the irradiation to the normal organ.

Through more precise targeting of the beam to tumors, doses to the tumors might be increased and to the non-target volumes can be reduced. Higher radiation doses have been shown to enhance tumor control and better sparing on non-target regions reduces the possibility of side effects after radiotherapy.

On-Board Imager®kV imaging system with cone-beam CT and imaging fusion technique, it provides us more precise localization information and better treatment quality and accuracy. Utilizing image guided radiation therapy needs to take x-ray and make correction before each treatment, thus it takes about four to five minutes more than the conventional radiation therapy treatment time.