GANTRY STUDIES FOR THE PROPOSED HEAVY ION CANCER THERAPY FACILITY IN HEIDELBERG

The Heavy Ion Cancer Therapy Facility HICAT [1] proposed for the clinic in Heidelberg will contain three treatment rooms - one treatment room will be equipped with a fixed horizontal beam line and two treatment rooms will contain heavy ion gantries. In parallel to the design of the accelerator facility, the heavy ion gantries were subject of detailed studies at GSI during the last years. Different layouts of the gantry ion optical system and of the gantry structure have been compared. The mechanical stability during rotation was analyzed and the effects of deformations on the beam transport were studied. Finally, an integrated gantry concept was found which satisfies the requirements on beam position stability in the ISO center. A gantry provides the capability to treat patients from arbitrary directions perpendicular to the original horizontal beam axis. Unfortunately, the magnetic rigidity of heavy ion beams with a suitable range is about three times higher than the rigidity of proton beams. Therefore, a main design criteria for heavy ion beam gantries is to restrict the growth of the geometrical extension and weight. However, the size and weight of the main dipole magnets is defined by the maximum allowed flux density in the iron yoke. Therefore, the total gantry weight is given by the weight of the beam guiding elements and the weight given by the the enhanced volume of the gantry structure. However, beside the layout of the ion optical system, a careful study of the mechanical properties is required. Gantry structure designs and analysis were performed by means of finite element programs. Such programs enable the calculation of mechanical stress and deformations for arbitrary gantry angles. The misalignment of the gantry magnets caused by structure deformations or by other reasons like temperature variations have been determined.