An on-line detection system for the external visualization of the stopping region in pion radiotherapy

External visualizations of the stopping region of negative pions in plexiglass have been obtained using an on-line detection system incorporating a multi-wire proportional chamber. One-dimensional projections of the stopping region were obtained with low background and good statistics with irradiation times of a few minutes and a deposited dose in the peak of 4-6 Rad. Results are presented for pion momenta from 140 to 185 MeV/c, with various momentum bites, and these are compared with expected ranges in plexiglass and measured depth-dose curves. An additional visualization in water has been carried out at a momentum of 180 MeV/c and a similar comparison made. The work was carried out at the biomedical pion channel πE3 of the SIN meson factory. (Auth.)