Dosimetry and radiobiology of negative pions and heavy ions

The advantages of using negative pion or heavy ion beams in radiation therapy are briefly reviewed. The contributions of a poster session from a clinical radiotherapy conference concerning progress with such beams is then summarised. The depth dose distributions of pion beams has not been found to be superior to protons. Additionally, pion radiobiology data have indicated lower RBE values and higher OER values compared to fast neutrons. Dose-average LET values are compared for neutrons, negative pions and heavy ions (helium, carbon, neon and argon). Heavy ions are found to have OER values much higher than the expected values of unity. In conclusion, biological effects such as RBE and OER of fast neutrons appear similar to those for some of the heavy ions; if dose localisation was the important criterion without changing the radiation quality from conventional low LET radiation, then the proton is the preferred choice of particle. (UK)