Abstract
Stereotactic irradiation is widely applied for treating brain tumors, AVM and so on. Stereotactic irradiation therapy is divided into stereotactic radiosurgery (SRS) and Stereotactic radiotherapy (SRT). SRS is radiotherapy utilizing a large dose with a single fraction, and SRT is hypofractionated radiotherapy. The Gamma Knife, liniac surgery systems and CyberKnife are all used for SRS. The Gamma Knife contains 201 small Co-60 sources. A metal frame and helmet are used to fix the patient's head and to deliver the precise dose to the target. Patients are usually treated with multi-isocentric planning to obtain the correct homogenous dose distribution. The Gamma Knife can only be applied for use in the brain region, and not for the neck region because of the metal frame and helmet. Several defferent linac surgery systems are commercially available. Patients are usually fixed to a linac couch with a metal frame. Multiple arcs with small sized cones are usually used to obtain the proper spherical dose distribution. Multiple isocentric planning is applied for non-spherical targets. A micro-multileaf system is also used. It is easy to obtain an arbitrary field adjusted to the shape of the target using the micro-multileaf. Multiple non-coplanar beams are used for this micro-multileaf treatment. The CyberKnife is a linear accelerator mounted on an industrial robot. It contains a target locating system (TLS). If there is any movement of the patient during treatment, the CyberKnife evaluates the movement and the robot maintains its possition on the target. Because of the TLS, an invasive metal frame is not needed. Non-isocentric treatment can be performed with the CyberKnife, and the target can be treated with conformal shape planning. Stereotactic radiotherapy is also applicable for tumors in the body, especially of the lung and liver. There are several systems to adjust the movement of the tumor due to patient's respiration. A body frame is also commercially available. The FOCAL system is a combination of CT and liniac. The location of the tumor is evaluated with CT before treatment and liniac therapy is done on the same table as the CT. RTRT is a combination of fluoroscopy and liniac. Tumor is continuously monitored with fluoroscopy, and a linac X-ray beam is delivered when the tumor is inside the treatment area. The CyberKnife also can be applied for tumors in the body. A robot evaluates the tumor location and the robot according to the movement of the tumor. The linac X-ray beam can be delivered continuously. Every hospital must choose the best system according to the number of patients and distribution of the disease
