Abstract: A radiation therapy system optimized for treating extremities such as the breast has unique geometrical features that enable the system to deliver an accurately located prescribed dose to a target volume while eliminating or reducing the collateral dose delivered to the rest of the patient. The patient lies in a prone position on a rotating, shielded table, with the anatomy to be treated protruding through an orifice in the table into the path of a radiation beam. An optional integral imaging system provides accurate target volume localization for each treatment session. Utilizing the effects of gravity on a prone patient maximizes the separation of a target volume within the breast to adjacent critical structures such as the chest wall, heart and lungs, thereby reducing long term complications not associated with the primary disease. A shielded interface surface between the radiation source and the patient reduces patient dose due to scattered or stray radiation.