A cryogenic source of negative pions for cancer therapy

The depth-dose distribution of a beam of negative pions is calculated. Special attention is given to the many pion-nucleus in-flight interactions that occur in the entrance plateau region. These interactions include elastic scattering, in-flight stars, and charge exchange. Using published cloud chamber and nuclear emulsion data the contribution to entrance dose of these processes is approximated. The results are in better agreement with several depth-dose experiments than previous calculations. The substantial dose contribution in the entrance region indicates that multi-field techniques will be necessary in order to take full advantage of the potential of pion beams for cancer therapy