抄録
Proton Medical Research Center of Tsukuba University employs a scattering method to obtain approoriate prooriate (almost flat dose distribution of 16cm in diameter on the treatment table) irradiation field for the proton beam therapy. A simple estimation shows that only 10% of protons impinging into the scatterer can reach the irradiation field. Collimators as well as other devices placed along course of the beam port interrupt the rest of protons. As is well known, energetic protons generate neutrons when they interact with matters. Some portions of these strongly penetrating neutrons cause an unexpected whole body irradiation of patients during the proton therapy. In this report, the neutron dose per unit proton target dose is estimated about 0.006 Sv/Gy for a typical treatment planning (the specific fluence and average energy of protons at the surface of the patient are about 1.1 x 109cm-2/Gy and 135 MeV respectively), and a strategy for reducing them is proposed.
