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 shapeat 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, anda 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 tofind (30) the sparsest subset of individual dose shots, so as to satisfy said one or more constraints (20).
