A method of using a computer system (100) to assist in programming a path for a surgical insertion into a skull, the method comprising: providing the computer system with a three-dimensional representation of the skull and crucial objects (781, 183) located within the skull, in which said crucial objects comprise anatomical characteristics to be avoided during surgical insertion； providing the computer system with a target location (770) for insertion into the skull； generating by the computer system a first set comprising a plurality of entry points (760), each entry point representing a superficial location in the skull, and each entry point being associated with a path from the entry point to the location Diana； discarding the entry points of the first set by the computer program to form a second, reduced set comprising a plurality of entry points, in which one entry point is discarded from the first set of entry points if the entry point has an angle that does not meet a condition of being substantially perpendicular to the surface of the skull； and for each entry point in the second set, evaluate by the computer system said entry point against a set of one or more criteria, in which the set of one or more criteria includes a risk factor based on the separation between the crucial objects and the path that is associated with said entry point； the method further comprising providing a plurality of target locations, and wherein said one or more criteria for evaluating a path include ensuring that the paths to the respective target locations do not conflict with each other, wherein two paths are considered to fall in conflict with each other if they pass within a predetermined distance from each other, and in which said guarantee includes, for a set of N target locations that have an arbitrary ordering: 1) start n = 1 2) select a nth target point 3) add the lowest risk path for the nth target point 4) evaluate to see if there is a conflict between the n selected pa
