Microdosimetry of multiport irradiation with the Stanford Medical Pion Generator

Microdosimetric measurements are presented for multiport negative pion irradiation of a 26-cm-diameter cylindrical water phantom at the Stanford Medical pion generator (SMPG). The data were obtained with a 1.27-cm-diameter spherical tissue equivalent (TE) proportional counter filled with TE gas to a pressure corresponding to an equivalent thickness, along a diameter, of 2.0 μm of unit density tissue. Beam configurations with the mean pion range greater than, equal to, and less than the phantom radius were studied. Dose-averaged lineal energies, anti y/sub D/, calculated with these data varied between 2.6 +- 0.2 and 63.5 +- 3.2 keV/μm