Clinical trials of boron neutron capture therapy (BNCT) are being carried out using theJapan Research Reactor No.4 (JRR-4) in Japan Atomic Energy Agency (JAEA). BNCT is a sort of radiationtherapy for an obstinate cancer like a malignant brain tumor. The BNCT clinical trial at JRR-4 has been carriedout since 1999. To carry out the clinical trials based on accurate dosimetry, JAEA Computational DosimetrySystem (JCDS), a treatment planning system for BNCT, was developed by JAEA. To predict the neutrons andphotons behavior around an irradiation field of a patient, JCDS creates a detailed 3D model of a patient usingmedical images, and then the 3D model is converted into a voxel model. Distributions of neutron flux thecorresponding several doses in the voxel model are determined using Monte Carlo transport code, MCNP.BNCT clinical trials for malignant brain tumor derived from a proper treatment plan with JCDS were begun atJRR-4 in October 2003. To enhance the accuracy of dosimetry calculations, JCDS has been improved to create adetailed voxel model consisting of minute voxel cells as small as 2x2x2mm. To calculate the distributions of thefluxes and doses effectively, JCDS has employed transport calculations with “mesh tally” option installed inMCNP version 5. By using the mesh tally option, the computing time can be shortened significantly. Applicationof the minute voxel calculation combined with mesh tally improves the accuracies of dose evaluation so that anoptimum treatment planning for not only the malignant brain tumor but also the head-&-neck cancer can besuccessfully performed.Keywords: BNCT, JRR-4, treatment planning system, MCNP, dosimetry. Improvement of Treatment Planning System At JAEA (JCDS)For Boron Neutron Capture TherapyH. Kumada1*, K. Yamamoto1, Peng Hong Liem2, A. Matsumura3 and Y. Nakagawa41: Japan Atomic Energy Agency, Japan2: NAIS Co., Inc, Japan3: University of Tsukuba, Tsukuba, Japan4: National Children’s Hospital, Japan*E-mail: kumada.hiroaki@jaea.go.jp
