title: An investigation of the characteristics of a negative pion beam by means of induced chromosome aberration in human peripheral blood lymphocytes.
abstract: The depth dose profiles of unstable chromosome aberrations were determined by irradiating blood samples at various depths in a plastic phantom exposed to a beam of negative pi mesons (pions). The pions were derived from an experimental beam line from the Nimrod 7 GeV proton synchrotron. With a momentum of 160 MeV/c and a spread of 15 per cent a Bragg profile was produced peaking at 13-9 cm. An ionization peak to plateau ratio of 1-6 was obtained and for cytogenetic damage this was increased to 2-9. Dicentric and acentric dose-response data from peak and plateau positions were fitted to Y=alphaD+betaD-2 models for comparison with data obtained from 60-Co gamma-rays and fission neutrons. With respect to 150 rads gamma-radiation, the r.b.e. values for the pion peak were 2-1 for dicentrics and 2-3 for acentrics. In the plateau the value for both aberrations was 1-5. At pion doses likely to be used as daily radiotherapy fractions, the aberrations predominantly resulted from single-track events, indicating little likelihood of interfraction recovery, particularly in the peak position. It is concluded that the biological damage characteristics of pion beams, as determined from a cytogenetic end-point, offer several features attractive to the radiotherapist.
mesh_terms: D002869:Chromosome Aberrations; D003037:Cobalt Radioisotopes; D004307:Dose-Response Relationship, Radiation; D004601:Elementary Particles; D005720:Gamma Rays; D006801:Humans; D066298:In Vitro Techniques; D008214:Lymphocytes / Q000528:radiation effects*; D009502:Neutrons; D011830:Radiation Effects
chemical_list: D003037:Cobalt Radioisotopes