3D Treatment Planning for 14 MeV Neutrons

Three-dimensional treatment planning is now widely used in radiotherapy with high energy photons. Special tools, for example beam's-eye view (BEV) and dose-volume histograms (DVH) are developed to simulate the shape and position of the beams and to evaluate the dose distribution in the target and the organs at risk. 3D visualisation is used to assess the dose distribution with respect to the target and the organs at risk. Standard blocks made from steel are used at our department to reduce the dose to critical organs. The ring model, originally developed for photon treatment, could be modified to be used with neutrons, too. This implies that the neutron dose is separated into its primary and secondary components, arising from concentric rings around the point of interest. A comparison between measurements in a water phantom and corresponding calculations demonstrates the attainable accuracy. For the DT neutron generator used for patients' treatment at our institution a commercially available treatment planning system was modified to enable the coplanar calculations of three-dimensional treatment plans. Furthermore, a visualisation system developed at our hospital is used to render the 3D dose matrix, together with anatomical data and the regions of interest. The mode of shaded surfaces and transparency simulates a three-dimensional impression of the rendered structures. A realistic case of a neutron treatment is used to clarify the different steps of the 3D treatment planning procedure and its implementation into clinical use.