Neutron beam characterization at the finnish BNCT facility:Measurements and calculations

A Boron Neutron Capture Therapy (BNCT) treatment facility with an epithermal neutron beam has been successfully completed at the Finnish FiR 1 TRIGA reactor at VTT, Espoo. The clinical trials on human patients were started in May 1999. The beam utilizes a specially developed moderator material FLUENTAL™ Extensive measurements and calculations have been carded out to characterize the neutron and gamma fields, both in the "free beam" and in tissue substitute phantoms. Despite the fairly low reactor power (250 kW) an epithermal fluence rate of 1.06 × 109 n cm-2 s-1 is achieved at the beam exit aperture with low fast-neutron contamination. The beam has been modeled in detail using the DORT transport code with the BUGLE-80 library. The neutron spectrum has been adjusted with the LSL-M2 code based on multiple-foil activation. Similar calculations and measurements have been performed by the Finnish BNCT team at the BMRR facility for direct comparison.