The present disclosure relates to a system, a method, a computer program and a computer readable medium for determining the thickness of a range shifter to attain target dose coverage in ion beam treatment, wherein the range shifter is for use in a machine for radiation treatment of a target volume, by: receiving, in a processor, input parameters comprising a radiation energy parameter, a range shifter material parameter, object geometry information, and beam characteristic parameters； and further calculating, for each of at least one delivery direction, a range shifter thickness, based on the input parameters, which will deliver the optimum dose conformity.
