High-LET pion dose contours under the LAMPF biomedical channel by plastic track detector scanning.

Cellulose-nitrate plastic track detectors have been tested as high spatial-resolution dosimeters at the Biomedical Channel of the Clinton P. Anderson Meson Physics Facility (LAMPF) at the Los Alamos Scientific Laboratory during pilot clinical trials with negative pi mesons (pions). Six plots of dose contours are presented. Reliable macrodosimetry with track detectors would in principle require detector calibration for the particular conditions of geometry and beam parameters in every case but it is interesting that absolute dose values, estimated from data taken with a quite different calibration geometry, were within 20% of agreement with dose values obtained by electronic dosimetry methods. The track detectors measure only the high linear energy transfer (LET) components produced by the pion beam; it is these components which are of special interest in the negative-pion therapy program. Plastic track detectors appear to have many favorable properties for pion dosimetry.