Figure 1.

Treatment plan for a petroclival meningioma, showing some of the main steps. Single beams of radiation penetrate mainly through the splanchnocranium so as to protect the brain. Trajectories through the eyeballs are excluded. The use of tuning structures (green circles): these tuning shells are used as artificial critical organs in the inverse planning algorithm. A specific dose is set for each shell in order to contain the lower dose distribution outside the planning treatment volume (PTV). This is a fundamental step of non-isocentric planning, in order to force the system to use a wide array of beams (hundreds) and to avoid dangerous peripheral radiation hot-spots.