I. Objective and Importance of the Project We have been using MC-50 cyclotron and NT-50 neutron therapy machine for treating cancer patients since 1986 at Korea Cancer Center Hospital. It is mandatory to measure accurately the dose distribution and the total absorbed dose of fast neutron for putting it to the clinical use. At present the methods of measurement of fast neutron are proposed largely by American Associations of Physicists in Medicine (Task Group 18), European Clinical Neutron Dosimetry Group, and International Commission on Radiation Units and Measurements. The complexity of measurement, however, induce the methodological differences between them. In our study, therefore, we tried to establish a unique technique of measurement by means of measuring the emitted doses and the dose distribution of fast neutron beam from neutron therapy machine, and to invent a standard method of measurement adequate to our situation. II. Scope and Contents of the Project For establishing a unique technique of measurement and inventing a standard method of measurement of fast neutron beam, 1. to grasp the physical characteristics of neutron therapy machine 2. to study the principles for measrement of fast neutron beam 3. to get the dose distribution (dose rate, percent-depth dose, flatness etc) throught the actual measurement 4. to compare our data with those being cited world-widely.