Induction of spinal cord paralysis by negative pi-mesons

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Abstract
As part of investigations on late non-neoplastic injury induced by negative pi-mesons (pions), a series of studies was performed using pion beams for the induction of spinal cord paralysis in the Fisher 344 rat. Groups of rats were exposed to 1, 5 or 15 daily doses of peak pions or X rays. Paralysis appeared earlier after treatment with pions than after X rays even in a comparison of groups with similar final incidences. A single dose RBE [relative biological effectiveness] for spinal cord paralysis of 1.3 was found. The RBE rises to a value of 3.2 if the total dose is given as a series of 15 daily exposures. These RBE are far larger than observed using other late injury endpoints, such as tubular degeneration in the kidney or fibrosis and sclerosis in the support structures of the colon for which the single dose RBE is less than 1.2. The biological and/or physical basis for the high sensitivity of the spinal cord to peak pions has not yet been resolved, but these data have suggested caution in exposing the spinal cord to peak pions in clinical trials.