Radiobiology of pions in comparison with other heavy particles.

Our recent data on late effects of pions in spinal cord, lung and rectum in rodents is presented with reference to other high-LET radiations. Unlike high-LET radiations such as neutrons and neon ions, the RBE for late effects of pions (up to 1.5) is not found to be significantly different from acute effects. Because of the potential of matching treatment volume (especially by using dynamic treatments) to the target volume by using pions and heavy ions, it is of utmost importance to study the tolerance of normal tissues to late effects as a function of volume. Such knowledge combined with pion and heavy ion dynamic treatment could lead to a further step in heavy particle radiotherapy.