A small tabletop stationary five-degree of freedom device such as a "robot" is used to define the treatment region by tracing the region under direct visualization and then to precisely deliver the treatment plan created by an automatic planning system by positioning a single low energy radiation source, or a plurality of low energy sources connected to each other in a predetermined parallel or similar geometry, each source equipped with blocking and attenuation mechanisms, at a plurality of positions in a planar fashion across or through a selected treatment field, thereby delivering a plurality of parallel overlapping beams indexed on a millimeter or submillimeter grid such that a concentration of dose is achieved at a variable depth in tissue relative to the dose where the radiation first enters the tissue and can be used to treat regions on or below the surface of tissue, in a cavity and underlying region created following a surgical resection, on or below the surface of an internal cavity, hollow viscus, or lumen, or deep in tissue adjacent to an inserted probe or conduit or catheter. By generating a plurality of overlapping beams indexed on a millimeter or submillimeter grid that converge on a target volume loaded with gold nanoparticles, a tumorcidal dose of radiation can be delivered in as little as a single session to tumor cells but not to normal cells within or outside the treatment volume. This approach also makes it possible to deliver serial radiosurgical treatments.