Therapeutic radiation source with increased cathode efficiency

A therapeutic radiation source, comprising:

• A. a radiation generator assembly, comprising:
• a. an electron source for emitting electrons to generate an electron beam along a beam path, said electron source including a thermionic cathode having an electron emissive surface, and
• b. a target positioned in said beam path, said target including means for emitting therapeutic radiation in response to incident accelerated electrons from said electron beam;
• and
• c. a substantially rigid housing enclosing said thermionic cathode and said target, wherein said housing defines a substantially evacuated interior region extending along said beam path between an input end and an output end of said housing.
• B. a source of optical radiation;
• and
• C. optical delivery structure having a proximal end and a distal end and adapted for transmitting to said distal end optical radiation generated by said source and incident on said proximal end, said optical delivery structure being adapted for directing a beam of said transmitted optical radiation upon a surface of said thermionic cathode, wherein said beam of optical 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;
• and
• wherein said thermionic cathode has a non-planar configuration adapted to allow incident optical radiation to undergo a plurality of absorption processes from a plurality of regions within said surface in succession.