November 11, 1997 This is a preprint of a paper intended for publication in a journal or proceedings. Since changes may be made before publication, this preprint is made available with the understanding that it will not be cited or reproduced without the permission of the author. Lawrence Livermore National Laboratory UCRL-JC-129097 PREPRINT Fast Monte Carlo for Radiation Therapy: the PEREGRINE Project This paper was prepared for submittal to the 1998 Radiation Protection and Shielding Division Topical Conference Technologies for the New Century Nashville, TN April 19-23, 1998 C. L. Hartmann Siantar, P. M. Bergstrom, W. P. Chandler, L. J. Cox, T. P. Daly, D. Garrett, R. K. House, E. I. Moses, C. L. Powell, R. W. Patterson, A. E. Schach von Wittenau