Optically driven therapeutic radiation source

A source of therapeutic radiation, comprising:

• A. a radiation generator assembly, including:
• a. an electron source for emitting electrons to generate an electron beam along a beam path, wherein said electron source includes a thermionic cathode having an electron emissive surface;
• and
• b. a target element positioned in said beam path, said target element being spaced apart from and opposite said electron emissive surface, said target element comprising at least one radiation emissive element adapted to emit therapeutic radiation in response to incident accelerated electrons from said electron beam;
• and
• c. a substantially rigid capsule, wherein said electron source and said target element are disposed within said capsule, and further wherein said capsule defines a substantially evacuated interior region extending along a beam axis between said thermionic cathode at a proximal end of said housing and a radiation transmissive window at a distal end of said housing;
• B. a source of laser radiation;
• C. a probe assembly coupled to said radiation generator assembly and including an optical delivery structure, said optical delivery structure having a proximal end and a distal end;
• wherein said optical delivery structure is adapted for transmitting laser radiation, generated by said source and incident on said proximal end, to said distal end, and for directing a beam of said transmitted laser radiation to impinge upon said electron emissive surface of said thermionic cathode, and wherein said beam of laser radiation has a power level sufficient to heat at least a portion of said surface to an electron emitting temperature so as to cause thermionic emission of electrons from said surface;
• D. one or more reflector elements disposed at predetermined locations along an inner surface of said capsule, said one or more reflector elements being operative to reflect incident laser radiation unabsorbed by said thermionic cathode back to said thermionic cathode.