Role of XCT in the radiotherapy

X-ray computed tomography is very useful in various aspects of treatment planping in radiotherapy. However, conventional CT has no means to transfer spatial information of irradiation beam to a patient body surface. There are several ideas for making a therapy oriented CT machine. We have developed a Beam Pointer System (BPS) which is a special apparatus to mark an irradiation fields on the patient skin. The BPS is an optical device operated under computer control of the CT scanner (Pfizer/AS and E 0450) and can be manipulated in an interactive mode using CT images that are displayed on a CRT. We believe this type of system is useful when the diagnostic CT is employed for treatment planning. (author)