Abstract: A method of optimizing a radiation treatment plan of ion treatment, in which the optimization procedure is interrupted, some but not all low-weight spots are discarded and the optimization procedure is resumed with a reduced set of spots. The weight of one or more remaining spots may be increased before resuming the optimization procedure, for example by adding the spot weight of one or more of the discarded spots to one or more of the remaining spots.

Abstract: A method of evaluating a radiotherapy treatment plan for ion based radiotherapy, is proposed, comprising the steps of determining multiple elastic scattering of ions for scattering angles in a first angular interval having an upper limit at a selected cut-off angle by means of a model for Coulomb scattering; determining multiple elastic scattering of ions for scattering angles in a second angular interval having a lower limit at the selected cut-off angle; determining the scattering for angles in a range comprising at least a part of the first angular interval and at least a part of the second angular interval, based on the results obtained for the first and second angular interval, respectively. The method avoids the double counting of particles at large scattering angles that occurs when using conventional methods.

Abstract: A method of performing dose calculations for ion radiotherapy compensating for tissue in which the density within a voxel may be inhomogeneous by approximating a portion of the voxel as an air cavity. For each dose voxel, the voxel is inscribed in a three-dimensional grid comprising a number of cells and the propagation of ions through the voxel is calculated based on the cell pattern in the at least one cell overlapping the voxel. Preferably, the voxel is inscribed in the three-dimensional grid in such a way that it overlaps at least one cell fully. Each cell comprises a first portion representing a first density corresponding to a density of a tissue and a second portion representing a second density corresponding to the density of air, the first and second portions forming a cell pattern.

Abstract: A system for determining a treatment plan in active ion beam treatment, to minimize unwanted dose, while maintaining or improving target dose coverage, whereby a beam is split into at least two sub-beams and where each sub-beam has a range shifter of different settings.

Abstract: A method of evaluating the robustness of a radiotherapy treatment plan for ion based radiotherapy, comprises the steps of: obtaining information related to the incident energy of ions that will stop in each voxel of the treatment volume; calculating a quantity value representative of the incident energy of these ions; and using the quantity values calculated for the first and second portion as a measure of the quality of the radiotherapy treatment plan, in particular its robustness. The information may include the mean incident energy for all ions, and/or an indication of the distribution of the energy values for all the ions.