Tumor Therapy with Heavy Ions at GSI Darmstadt

In comparison to conventional photon therapy heavy-ion beams offer favourable conditions for the treatment of deep-seated local tumors. The physical depth-dose distribution in tissue is characterized by a small entrance dose and a distinct maximum (Bragg peak) near the end of range with a sharp fall-off at the distal edge. The well-defined range and the small lateral beam spread make it possible to deliver the dose with millimetre precision. In addition, heavy ions have an enhanced biological effectiveness in the Bragg peak region, which is caused by the dense ionization and the resulting reduced cellular repair rate. Furthermore, heavy ions offer the unique possibility to apply Positron Emission Tomography (PET) techniques for an in-vivo range monitoring of positron-emitting isotopes like C which are formed in nuclear fragmentation reactions. The pilot therapy unit at GSI started operation in December 1997 using C ions with energies of 80-430 MeV/u from the heavy-ion synchrotron SIS-18 and a novel fully active rasterscan system for beam delivery. So far more than 260 patients were treated with very promising clinical results. The indications comprise mainly inoperable and radio-resistant tumors of the skull base (chordoma, chondrosarcoma and others) which are located near sensitive organs such as the brain stem or the optical nerve. The treatments with a median tumor dose of 60 Gye delivered in 20 fractions were well tolerated and no significant side effects occurred. Local tumor control rates after three years follow-up time were 100% for chondrosarcomas and 81% for chordomas. The construction of a new dedicated proton/ion treatment centre (HIT) at the Radiological Clinic in Heidelberg with a planned capacity of more than 1000 patients per year has started in spring 2004. It will be equipped with one 360° isocentric Gantry system and two additional treatment rooms with horizontal beam lines. Clinical operation is expected to begin in 2007.