The accurate calculations of the absorbed dose distribution in patients irradiated by clinical beams is very important in radiotherapy treatment. Currently, the most accurate method of radiation therapy dose calculation is the Monte Carlo (MC) simulation of radiation transport, which requires detailed information on the character of the beam in the form of a phase-space file, which imposes very high requirements for disk space and CPU time. Monte Carlo calculations of dose distribution using multiple-source models is an alternative to using the phase-space information as direct input to the dose calculation code.