Radiotherapy systems using proton and carbon beams.

Abstract

Radiotherapy using proton beams (proton therapy) is rapidly taking an important role among the techniques used in cancer therapy. At the end of 2007, 65.000 patients had been treated for cancer by proton beams in one of the 34 proton therapy facilities operating in the world. When compared to the now classical IMRT, and for a similar dose to the tumor, proton therapy provides a lower integral dose to the healthy organs surrounding the tumor. It is generally accepted that any reduction of the dose to healthy organs reduces the probability of radiation induced complications and of secondary malignancies. Proton therapy equipment can be obtained today from well established medical equipment companies such as Varian, Hitachi or Mitsubishi. But it is a Belgian company, Ion Beam Applications of Louvain-la-Neuve that is the undisputed leader in this market, with more than 55% of the world installed base. In addition to the now classical proton therapy equipments, using synchrotrons or cyclotrons as accelerators, new solutions have been proposed, claiming to be more compact and less expensive. A small startup company from Boston (Still Rivers) is proposing a very high magnetic field, gantry mounted superconducting synchrocyclotron. The us Company Tomotherapy is working to develop a new accelerator concept invented at Lawrence Livermore National Laboratory: the Dielectric Wall Accelerator. Besides proton beam therapy, which is progressively becoming an accepted part of radiation therapy, interest is growing for another form of radiotherapy using ions heavier than protons. Carbon ions have, even to a higher degree, the ballistic selectivity of protons. In addition, carbon ions stopping in the body exhibit a very high Linear Energy Transfer (LET). From this high LET results a very high Relative Biological Efficiency (RBE). This high RBE allows carbon ions to treat efficiently tumors who are radio-resistant and which are difficult to treat with photons or protons. The largest experience in carbon beam therapy comes from Japan, from the National Institute for Radiation Science (NIRS) in Chiba, where more than 4000 patients have been treated with carbon beams. In Europe, carbon beam therapy has been tested on a limited number of patients in GSI, a national laboratory for heavy ion research in Darmstadt. A clinical carbon therapy center has been developed by GSI and the prototype is located at the German National Cancer Research Center (DKFZ) in Heidelberg. This center (HICAT) is close to being completed, and should treat patients in 2009. Another national carbon therapy facility is under construction in Pavia (Italy), and is build by a group of Italian physics laboratories. Siemens has obtained the intellectual rights of the GSI design in Heidelberg, and has sold two other carbon therapy systems in Germany, one in Marburg and one in Kiel. All existing systems for carbon therapy use cyclotrons as accelerators. IBA has introduced the innovative concept of using a superconducting cyclotron for the acceleration of carbon ions for radiotherapy. The superconducting cyclotron technology should allow a reduction of the size and cost of carbon therapy facilities.