title: An improved optical backpointer for isocentric radiotherapy machines.
abstract: A simple optical backpointer has been designed as a retrofit for isocentric radiotherapy machines. Two lasers are used to project two fan beams of light which intersect in line with the central ray of the radiation beam. The system is mechanically rugged, and the projected cross is visible even in room light.
mesh_terms: D006801:Humans; D007834:Lasers; D010315:Particle Accelerators; D011878:Radiotherapy / Q000295:instrumentation*