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Heavy charged particle beams can be widely used for cancer therapy if control in heterogeneous tissue is proved practical. A beam of protons at 200 million electron volts has been visualized in plastic and in a living animal by using an on-line positron camera. The fraction of the activity retained in the radiation site was found to be at least 70 percent of that produced in a dead animal. The sensitivity of the technique was established for a typical geometry.

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Accurate bolus is needed for extension of Bragg-peak therapy. Proton beam-stopping profiles in a lucite-styrofoam-tissue phantom and in a Rando phantom were recorded photographically. Air volumes caused the largest distortions. Lucite bolus was cut to achieve desired beam-stopping profiles. Verification of bolus effect in situ will be important to control beam penetration within 5 mm.