An improved x-ray generation system produces a converging or diverging radiation pattern particularly suited for substantially cylindrical or spherical treatment devices. In an embodiment, the system comprises a closed or concave outer wall about a closed or concave inner wall. An electron emitter is situated on the inside surface of the outer wall, while a target film is situated on the outside surface of the inner wall. An extraction voltage at the emitter extracts electrons which are accelerated toward the inner wall by an acceleration voltage. Alternately, electron emission may be by thermionic means. Collisions of electrons with the target film causes x-ray emission, a substantial portion of which is directed through the inner wall into the space defined within. In an embodiment, the location of the emitter and target film are reversed, establishing a reflective rather than transmissive mode for convergent patterns and a transmissive mode for divergent patterns.