Patent Number: 
Section: claims

1. A radiation therapy system comprising:a megavoltage radiation source and beam modulator producing a programmable radiation beam;a rotatable patient positioning system, comprising:a patient interface surface; andan aperture to permit passage of the anatomy to be treated through the patient interface surface;means to move the patient positioning system about a substantially vertical axis with respect to said radiation source;a beam stop to substantially absorb the radiation beam which bypasses or is transmitted through the patient during operation;an integrated shielding system cooperating with the patient interface surface configured to shield the patient, except for the anatomy to be treated, from substantially all direct and scattered radiation from the radiation source, beam modulator, and beam stop. 2. The radiation therapy system of claim 1 further including x-ray imaging means for visualizing the patient anatomy. 3. The radiation therapy system of claim 1 where the system is mounted in a mobile enclosure. 4. The radiation therapy system of claim 1 including a shielded enclosure which encloses the radiation source and modulator where the patient interface surface cooperates with the enclosure to shield the patient, except for the anatomy to be treated, from substantially all direct and scattered radiation from the radiation source, modulator and beam stop. 5. The radiation therapy system of claim 1 where said radiation source is a linear accelerator. 6. The radiation therapy system of claim 1 where the anatomy to be treated is a breast.