The present invention concerns a radiation inverse treatment planning system for a linear accelerator, comprising: - a radiation source, configured for delivering individual dose shots (aj), 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 (102), - a memory (106) coupled to the data bus system (102), wherein the memory (106) comprises a computer usable program code, and - a processing unit (104) coupled to the data bus system (102), wherein the processing unit (104) is configured to execute the computer usable program code to - pre-compute (10) a set of individual dose shots (aj), - associate (40) a weight (sj) to each individual dose shot (aj), based on one or more constraints (20), characterised in that the processing unit (104) executes the computer usable program code to - find (30) the sparsest subset of individual dose shots, to satisfy said one or more constraints (20).
