The positron-emitting activation of tissue by a-particle beams has been studied, using the annihilation y-ray coincidence detection technique, and the Anger positron camera.The decay spectrum in tissue following irradiation by 53 Mev a-particles from the Berkeley 88-inch cyclotron has been measured, as well a3 a visualization of the activation pattern resulting from a 910 Mev a-particle beam stopping in a tissue-like plastic phantom, a t the Berkeley 184-inch synchrocyclotron. Also studied were the activation patterns resulting from transmission of 910 MeV a-beams through a wax heed phantom, end the activation pattern in patients' heads resulting from one sitting for the pituitary ablation therapy technique. With alight improvements in resolution and sensitivity, en " on-line " positron camera technique could be useful for alignment of the end of the beam track in &eggpeak therapy with heavy charged particles. There are other novel applications which might be possible, using tissue activation techniques.

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The doses from the cobalt-60 teletherapy machines were measured using the FBX and secondary-standard dosemeters of Farmer-Baldwin type. The FBX dosemeter contained 0.20 mM ferrous ammonium sulphate, 5.0 mM benzoic acid and 0.20 mM xylenol orange in 0.05 N sulphuric acid. The values were compared with the values from a Fricke dosemeter and a graphite chamber used as primary standards. The values of the FBX, Fricke and graphite chambers agreed. There were, however wide differences among the different secondary-standard dosemeters themselves and with the FBX dosemeter. The FBX dosemeter was used for the measurement of central axis depth dose distributions for 5, 8, 10, 20 and 30 MeV electron and 42 MV x-ray beams.

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