Calculation of pion dose distributions in water

Abstract

Techniques for calculating negative pion beam depth and off-axis dose distributions in a water pantom were developed at the Clinton P. Anderson Meson Physics Facility in Los Alamos, USA. The superposition of the unmodulated depth-dose curve produced modulated depth-dose curves. The addition of the collimator neutron dose, which depended on field size, to the modulated depth-dose curve yielded the collimated depth-dose distributions. Off-axis dose distributions under a collimator were produced by calculating the distortion of the uncollimated beam caused by multiple Coulomb scattering and beam phase space. Several comparisons of calculated and measured distributions were in agreement to .+-. 3% of peak dose or .+-. 3 mm for a particular dose contour. These distributions were modified by computerized tomography to give patient isodose distributions.