Dose outside the treatment volume for irradiation with negative pions

Irradiation of humans with negative pions requires a knowledge of the absorbed dose and radiation quality outside the primary pion beam. In conjunction with early clinical trials at LAMPF, experimental data have been obtained with microdosimetric techniques and multiwire proportional counters. Theoretical calculations have been made for the neutron contribution to the dose and are consistent with these data. Measurements were made within a 40 cm*51 cm*76 cm water phantom for a negative pion beam of initial momentum of 170 MeV/c, Delta p=+or-3 MeV/c. The absorbed dose outside the treatment volume is the result of: (1) neutrons and photons from the pion interactions, (2) treatment room background and (3) peripheral muons, electrons and pions in the primary beam.