1. A radiation inverse treatment planning system for a linear accelerator, comprising: a radiation source, configured for delivering individual dose shots, each individual dose shot having a predetermined location and incidence angle inside and/or outside a target area, a size and a shape at least a data bus system, a memory coupled to the data bus system, wherein the memory comprises a computer usable program code, and a processing unit coupled to the data bus system, wherein the processing unit ( 104 ) is configured to execute the computer usable program code to pre-compute a set of individual dose shots, associate a weight to each individual dose shot, based on one or more constraints, characterised in that the processing unit executes the computer usable program code to find the sparsest subset of individual dose shots, so as to satisfy said one or more constraints.