Radiobiological Background for Negative Pion and Heavy Ion Therapy on Cancers

Abstract

Recent advances in radiotherapy have been remarkable. However, there are some tumors which are incurable with conventional radiation therapy because of their histological features, localization and the like. In addition, conventional radiations such as photons, gamma rays or electrons show several disadvantages to bring tumors to cure. Hence more and more attention is being paid to new modalities such as fast neutrons, protons, negative pions and heavy ions, which are expected to overcome some of the defects of the conventional radiations. Except for fast neutrons, these particle radiations show excellent physical dose localization in tissue. Moreover, in terms of biological effects, they demonstrate several features compared to conventional radiations, namely low oxygen enhancement ratio ( OER), high value of relative biological effectiveness (RBE), smaller cellular recovery, larger therapeutic gain factor (TGF) and less cell cycle dependency in radiation sensitivity. In the present paper the biological effects of pions on murine tumor cells are shown comparing to the effects of conventional radiation, or heavy ions (Ne or Ar ions).