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 of muliport pion irradiation using the Stanford Medical Pion Generator (SMPG). Chinese hamster cells (HA-1) were suspended in a tissue-equivalent 25% gelatin/medium solution. Hypoxic and aerobic HA-1 cells were irradiated simultaneously in a cylindrical water tank at either 4 or 16 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, and 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 survival values very close to those obtained with similar doses of 85 kV X-rays. Preliminary studies with large irradiation volumes in broadened pion stopping regions indicate RBEs significantly > 1 for survival > 50%. Supporting microdosimetric data with the SMPG are consistent with the radiobiological results.