[en] 1 - Description of program or function: PTRAN, Version 1.1, uses a Monte Carlo program to calculate the transport of proton beams through extended media. The PTRAN code uses 50 to 250 MeV beams through water phantoms. Multiple scattering and Coulomb interaction energy loss mechanisms are taken into account along with nonelastic nuclear interactions. PTRAN calculates deposition of energy as a function of depth and radial distance from the beam, energy spectra of the primary protons as function of depth. Both 1 and 3 dimensional calculations are available. 2 - Method of solution: The PTRAN system uses several cross-section preparation programs and two main codes, PTRAN3D and PTRAN1D. The heart of the calculations is the Monte Carlo model which is based on the condensed-random-walk method (BERGER, 1963), and takes into account the following types of events occurring in successive short track segments: (a) energy-loss straggling in Coulomb collisions with atomic electrons, (b) multiple-scattering deflections due to elastic scattering by atoms, and (c) energy loss in nonelastic nuclear reactions. Data preparation programs facilitate the sampling of energy losses (VAVILOV, 1957) and angular deflections (MOLIERE, 1948). The initial proton stopping powers and ranges in water use PSTAR (NISTIR 4999, RSIC PSR-330). 3 - Restrictions on the complexity of the problem: The codes PTRAN1D (PTRAN1DX and PTRAN1DY) and PTRAN3D are memory intensive, and need 7.5 Mbytes of RAM to execute. The support codes, data conversion and preparation codes (PTSUM, PARAM4, MPREP, VPREP, MCON, VCON) need 4 Mbytes RAM. The code PTRAN3D ran an example that took 56 minutes on a 80486/87 50 MHz machine. The math co-processor is mandatory with the executables supplied which used the Lahey Fortran F77L3 compiler and Phar Lap DOS Extender/Linker