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The comparative narcotic effects of argon, nitrogen and helium have been previously studied by Behnke (1940) and by Behnke & Yarbrough (1938, 1939. Exposure up to 10 atm. of either air or an 80% argon, 20%.oxygen mixture produces progressive narcotic effects in man. These effects are attributed to the dissolved inert gases, nitrogen and argon. Breathed in equivalent concentration, argon has approximately twice the narcotic effect of nitrogen and is twice as soluble as nitrogen in water and in fat. The fat-water solubility ratio of the two gases is nearly the same. Helium, on the other hand, with its lower solubility in water and fat has negligible narcotic effects when compared with argon and nitrogen.

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Since 1954, 840 patients have been treated at Lawrence Berkeley Laboratory with stereotactic charged-particle radiosurgery of the pituitary gland. The initial 30 patients were treated with proton beams; the subsequent 810 patients were treated with helium ion beams. In the great majority of the 475 patients treated for pituitary tumors, marked and sustained biochemical and clinical improvement was observed. Variable degrees of hypopituitarism developed in about one-third of patients treated solely with radiosurgery. In the earlier years of the program, 365 patients underwent radiosurgery to treat selected systemic diseases by inducing hypopituitarism. Focal temporal lobe necrosis and cranial nerve injury occurred in about 1% of patients who were treated with doses less than 230 Gy.

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With confluent cultures of the C3H10T1/2 mammalian cell line, we have investigated the effects of heavy-ion radiation on neoplastic cell transformation. Our quantitative data obtained with high-energy carbon, neon, silicon, argon, iron, and uranium particles show that RBE is both dose- and LET-dependent for malignant cell transformation. RBE is higher at lower doses. There is an increase of RBE with LET, up to about 100-200 keV/micron, and a decrease of RBE with beams of higher LET values. Transformation lesions induced by heavy particles with LET values greater than 100 keV/micron may not be repairable in nonproliferating cells. RBE for slow and nonproliferating cells may be much higher than for actively growing cells.