Evaluation of neutron irradiation field for boron neutron capture therapy by using absorbed dose in a phantom.

Abstract

The method of an evaluation for the dose characteristics of BNCT is presented, and an eccentric core design for the TRIGA-II reactor is proposed. We have defined the "irradiation time" as the time of irradiation in which the "maximum 1 microgram/g dose" becomes 3,000 RBE-cGy, because we assumed that the normal tissue contained 1 microgram/g 10B. We have also changed the RBE values and calculated the absorbed dose in the "irradiation time" by using an arrangement including both a facility structure and a body phantom. Moreover, we have modified the dose criteria for BNCT as follows: The "eye dose," "total body dose," and "except-head dose" should be less than 200, 100, and 50 RBE-cGy, respectively. We have added one more criteria for BNCT-that the thermal neutron fluence at the tumor position (5 cm from the surface) should be over 2.5 x 10(12) n/cm2 in the "irradiation time." The distance from the core side to the irradiation port is a very important factor to design a neutron irradiation field for BNCT. We can get the acceptable dose for BNCT with only 1-h irradiation by using a 100 kW reactor if we can get the irradiation port at the distance of 120 cm from the core side.