Treatment planning for heavy ion radiotherapy: clinical implementation andapplication

The clinical implementation and application of a novel treatment planning s ystem (TPS) for scanned ion beams is described, which is in clinical use fo r carbon ion treatments at the German heavy ion facility (GSI). All treatme nt plans are evaluated on the basis of biologically effective dose distribu tions. For therapy control, in-beam positron emission tomography (PET) and an online monitoring system for the beam intensity and position are used. The absence of a gantry restricts the treatment plans to horizontal beams. Most of the treatment plans consist of two nearly opposing lateral fields o r sometimes orthogonal fields. In only a very few cases a single beam was u sed. For patients with very complex target volumes lateral and even distal field patching techniques were applied. Additional improvements can be achi eved when the patient's head is fixed in a tilted position, in order to ach ieve sparing of the organs at risk. In order to test the stability of dose distributions in the case of patient misalignments we routinely simulate the effects of misalignments for patie nts with critical structures next to the target volume. The uncertainties i n the range calculation are taken into account by a margin around the targe t volume of typically 2-3 mm, which can, however, be extended if the simula tion demonstrates larger deviations. The novel TPS developed for scanned ion beams was introduced into clinical routine in December 1997 and was used for the treatment planning of 63 pati ents with head and neck tumours until July 2000. Planning strategies and me thods were developed for this tumour location that facilitate the treatment of a larger number of patients with the scanned heavy ion beam in a clinic al setting. Further developments aim towards a simultaneous optimization of the treatment field intensities and more effective procedures for the pati ent setup. The results demonstrate that ion beams can be integrated into a clinical environment for treatment planning and delivery.