MAMMALIAN-CELL SURVIVAL STUDIES CHARACTERIZING MULTIPORT NEGATIVE PI-MESON IRRADIATION WITH THE STANFORD MEDICAL PION GENERATOR (SMPG)

Radiobiological measurements have been made under various conditions o f muliport pion irradiation using the Stanford Medical Pion Generator (SMPG). Chinese hamster cells (HA-1) were suspended in a tissue-equiva lent 25% gelatin/medium solution. Hypoxic and aerobic HA-1 cells were irradiated simultaneously in a cylindrical water tank at either 4 or 1 6-degrees-C. Irradiation at the focus of 60 converging pion beams, at a peak dose rate of 6 rads/min, gave relative biological effectiveness (RBEs) of 2.8, 1.8 and 1.4 at 50, 20 and 5% survival, respectively, a nd an oxygen enhancement ratio (OER) of 1.7. Plateau irradiation with crossing pion beams, at a peak dose-rate of 3 rads/min, resulted in su rvival values very close to those obtained with similar doses of 85 kV X-rays. Preliminary studies with large irradiation volumes in broaden ed pion stopping regions indicate RBEs significantly> 1 for survival > 50%. Supporting microdosimetric data with the SMPG are consistent with the radiobiological results.