Measurement of stopping power ratios for 60 MeV positive or negative pions

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Abstract
Pion stopping power ratios are essential parameters for pion radiotherapy [in humans] treatment planning. The validity of scaling proton stopping powers to pions is questioned since the pion mass is intermediate between the electron and proton masses. Direct measurements of stopping power ratios with respect to water were made for 60 MeV pions of both charges in Teflon, Plexiglas, nylon, paraffin, gelatine, tissue-equivalent plastic (Shonka A150), graphite, Al, steel and Cu. Corrections for multiple scattering and energy dependence of the stopping power are applied. Measured stopping power ratios at an accuracy of 0.6% are within the limits of experimental error with stopping power ratios calculated from the Bethe-Bloch equation using elemental I-values and Bragg additivity.