Tumor therapy with carbon ion beams.

Beams of heavy charged particles like protons or carbon ions represent the optimum tool for the treatment of deep seated, inoperable and radioresistant tumors growing in close vicinity to organs at risk. In contrast to photon therapy, the dose deposited by heavy charged particles increases with the penetration depth, culminating in a sharp maximum at the end of the particle range - the Bragg peak. This peak can be shifted in depth by energy variation and distributed laterally through magnetic deflection of the particle beam, thus allowing a precise and conform irradiation of the selected target volume. Furthermore, carbon ions offer the most conform irradiation due to their lower lateral scattering when compared to protons. In addition to this excellent physical selectivity, the biological efficiency concerning cell killing increases towards the end of carbon ion range. Therefore, the high dose at the Bragg peak is further enhanced by an increase in biological efficiency. Finally, by applying PET techniques, an in-situ dose localization control can be performed by tracing the small amount of beta⁺ emitters (¹¹C, ¹⁵O, ¹⁰C) which are produced in nuclear fragmentation reactions between the ¹²C projectiles and atomic nuclei in the target volume. A pilot tumor therapy unit that fully exploits the advantages of carbon ions is under operation at GSI since December 1997 and has now treadet more than 70 patients. Its mayor goal is to demonstrate the safe and routine application of charged particle beams for radiotherapy.