The Heidelberg Ion beam Therapy center (HIT) offers charged particle cancer treatment with proton and carbon ions. More than 2000 patients have been treated at two horizontal fix beam lines and one fully-rotational gantry place since the start of operation in November 2009. The particular ballistics of the beam particles allows for a highly conformal energy deposition in the target volume at a better sparing of the surrounding healthy tissue compared to conventional photon therapy. The energy of the charged particles has to be chosen such that they are completely absorbed within the target volume. Thus, verification methods commonly known from the photon world, which rely on the measurement of primary beam radiation exiting downstream the patient, are not applicable. There are, however, several approaches to detect secondary particles, generated in interactions between the primary beam and the patient tissue and able to emerge the patient, to extract information about the actual beam range. The most extensively applied method in clinical practice exploits the generation of positron emitting radionuclides in the irradiated tissue, which can be monitored shortly after beam delivery with a conventional PET/CT scanner. For this purpose, a commercial PET/CT has been installed at HIT in close vicinity to the irradiation places. Selected patients receive a post-irradiation PET/CT-scan after one or several treatment fractions in order to verify in-vivo the actual beam range and field position.

Since the spatial distribution of the tissue activation does not directly correlate with the dose distribution, which is the quantity to be verified, the assessment is based on a comparison of the measurement to an activity prediction. This prediction is derived from Monte-Carlo calculation methods under the assumption of a correct beam application according to the patient-specific treatment planning.

HIT represents together with the project partners from the Ludwig-Maximilians-University Munich the interface to particle therapy in the SPARTA project. HIT is responsible for the compliance and integration of particle-therapy specific software demands in the context of image registration and segmentation and development of an efficient data management concept under the technical support from the project partner FME. The main goal of HIT in the frame of SPARTA is the development of a decision support system, which will be able to interpret range verification results under consideration of various uncertainties, therefore providing a reliable in-vivo assessment of beam range, which should support medical physicists and radio-oncologists in view of adaptive treatment decisions.