Calculation of the dose induced in tissue by negatively charged pion beams

Calculations have been carried out using the Monte Carlo radiation transport code HETC to determine the spatial distribution of the absorbed dose produced in tissue by monoenergetic negatively charged pion beams. The depth dependence of the absorbed dose has been computed for narrow (zero width) negative pion beams incident normally on one side of a slab of tissue 60 cm thick. Beam energies of 53, 82 and 108 MeV (corresponding to ranges in tissue of approximately 10, 20 and 30 cm) were used. For the beam having a range of 20 cm, the absorbed dose as a function of the lateral distance from the beam axis has also been computed. The use of the results from monoenergetic beams to synthesize the incident energy distribution needed to produce desired depth-dose distributions is discussed and, as an example, the energy spectrum of the incident beam required to produce a uniform absorbed dose over the depth interval from 20 to 30 cm is computed.