Abstract
The possibillty of using beams of negative pi mesons for the treatment of tumors is considered. Possible advantages of pion beams are considered. Biological tissue is made up of hydrogen, carbon, nitrogen, and oxygen. When a pi -meson is brought to rest in such a medium it may be captured by any one of these atoms. When captured by hydrogen the resulting mesic atom migrates a short distance in the tissue until it encounters a heavier nucleus to which the pi / sup -/ is transferred. As a result, all the mesons interact before decaying with one or another of the nuclei C/sup 12/, N/sup 14/ or O/sup 16/ >s. In such interactions, about 20% of the total rest-energy of the meson, that is sbout 30 Mev, appears in the form of alpha particles and protons, nearly all of which have ranges less than 1 mm in biological materials. A further 40 Mev is expended in breaking up the nucleus, and the remaining 70 Mev is carried off as fast particles, mostly neutrons, of which about 60 or 70% will escape from the tissue without interacting. Advantages of using beams of negative pi -mesons in the treatment of tumors aremore » based on the fact that meson capture by light elements, especially C/sup 12/ and O/sup 16/, leads to an exceptionally large release of energy in the form of short-range a particles. The range of alpha pi /sup -/ meson of 52 Mev is about 10 cm in biological tissue, the maximum depth at which it is commonly necessary to irradiate tumors in the human body. If such a beam is homogeneous in energy, there will be a straggling in range of about 2.5 mm. The advantages of such a beam are illustrated by a calculated radiation field due to an initially parallel beam of 52 Mev. Results are compared with the comput field due to gamma rays. Available data on biological effects and dosimetry are reviewed. For a beam of pi /sup -/ mesons, the damage per unit volume is many times greater in the tumor than in adjoining regions, and the total damage in the tumor region appreciably exceeds that in the whole of the surrounding body tissue. The advantages appear to be very great. (C.H.)« less
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