Abstract: Process for determining the configuration or configurations [treatment time (TT.sub.i)/diameter (.phi..sub.i,f) of each collimator] of a helmet for stereotactic radiosurgery, to which can be fitted an plurality of collimators focused on an irradiation isocenter, consisting in automatically optimizing, through iterative dose calculation, the dose (D.sub.p) received at predetermined optimization points (M.sub.p), by modifying, in the course of the successive iterations, the treatment time (TT.sub.i) of at least one shot (i) and the diameter (.phi..sub.i,f) of at least one collimator (C.sub.f) of at least one shot (i), and by calculating, at each iteration, an objective function (OF) having as variables the differences between the calculated dose (D.sub.p) and the expected dose (ED.sub.p) for each point of optimization (M.sub.p), iterative calculation of the doses being carried out automatically until the objective function (OF) satisfies a predetermined optimization criterion.