Radiobiologic properties of pions and heavy ions. A comparison.

1. Depth-dosage distributions of pions and heavy ions are similar, but the dose fall-off near the range is much steeper for heavy ions compared to pions. 2. Radiation quality and hence biologic effects of heavy ion beams in the peak region depend only on peak width, whereas for pion beams because of fast neutrons from stars, the radiation quality may depend not only on peak width but also on beam size. 3. For neon and argon ions, the biologic effects of fractionated doses in proliferating cells are found to be more effective than for single doses. Such an effect was not observed for either fast neutrons or for pions. 4. Radiobiologically, pion beams are similar to helium and carbon ions.