Is there a role for heavy ion beam therapy?

The aim of this contribution is to review the radio-oncological rationale of heavy ion beam radiotherapy in the management of cancer. Protons and helium ions are being investigated because of the improved dose distributions, perhaps superior in many clinical situations to those obtainable with photons or electrons. Heavy ions also bear the advantage of superior dose distribution and may additionally provide higher biological effectivity. A substantial database of historical results supports the hypothesis that conformal radiotherapy is superior to conventional radiotherapy. For the selection of patients for ion beam therapy, the following questions have to be evaluated: Can any significant radiation morbidity by conventional treatment expected? Is the radiation morbidity caused by unintended irradiation of non-target tissue outside the planning target volume? Can the tumor control be improved due to dose escalation with less radiation morbidity? A substantial number of patients have been treated by light ion radiotherapy. There are only a few clinical trials attempting to compare conventional photon radiotherapy with light ion radiotherapy. Clinical results with heavy ions such as carbon ions seem very promising in certain tumors. However results of randomized trials are still to be seen. Clearly the control arm has to be designed to be as close as possible to the optimal photon/electron treatment methods in use. The feasibility of heavy ion treatment has been demonstrated worldwide, with more than 10,000 patients. In the near future more centers worldwide will start patient treatments. The wider availability of light ion beams for clinical use will enable the establishment of a database of clinical results and the elucidation of the role of heavy ion beams in the treatment of cancer.