gms | German Medical Science

Protontherapy is developing very rapidly while the results obtained with carbon ions on about 5000 patients indicate the superiority of these light ions in the control of radioresistant tumors. More and more radiation oncologists express the wish to acquire state-of-the-art protontherapy centres – featuring more than one gantry – and in a second phase, to possibly upgrade them by accelerating carbon ions to 400-430 MeV/u. The ‘dual’ centre here described fulfills these requirements.

Since 1993 TERA is working on the development of new fast-cycling accelerator complexes dubbed ‘cyclinacs’, which are best suited to treat moving organs with the multi-painting spot scanning technique. A cyclinac is the combination of a cyclotron (which can be used also for other valuable medical and research purposes) followed by a high gradient linear accelerator powered by many independently controlled klystrons, so that the range of the particles can be varied by ±10 mm in only 1–2 milliseconds. Following the successful construction and test of a 3 GHz linac prototype, a proton cyclinac is at present offered commercially by Applications of Detectors and Accelerators to Medicine (A.D.A.M. SA, Geneva).

The TERA ‘dual’ centre consists of a commercial Electron Beam Ion Source (from Dreebit Gmbh), a superconducting synchrocyclotron and a high-gradient linac. The source delivers both C⁶⁺ and H₂ ⁺ ions at the desired repetition rate (400 Hz). At the same rate, the synchrocyclotron accelerates the ions to 230 MeV/u (K_bending = 920 MeV), the energy needed for proton therapy. The machine features an azimuthally symmetric and radially decreasing magnetic field (central value of 5 Tesla), a mechanical radio frequency modulation by a rotating capacitor and a regenerative beam extraction system. This choice was driven by the possibility to work in pulsed mode, limit the size of the magnet and the power consumption of the radiofrequency system to less than 25 kW.

The 230 MeV/u carbon ions have a 12 cm penetration range in water and can be used for shallow tumours. The linac (possibly installed in a second phase) accelerates the ions to 430 MeV/u, corresponding to a 32 cm range. Various linacs are under design under the name CABOTO (CArbon BOoster for Therapy in oncology). Two Standing Wave Linacs at 3 GHz and 6 GHz and one Travelling Wave Linac at 9 Ghz. Frequencies higher than 3 GHz have been chosen to limit the power consumption of the complex to about 350 kW. This work is part of a collaboration with the CLIC group working at CERN on very high-gradient electron-positron colliders.