International Conference on Advances in Nuclear Science and Engineering in Conjunction with LKSTN 2007(93-97) Improvement of Treatment Planning System At JAEA (JCDS) For Boron Neutron Capture Therapy H. Kumada 1 *, K. Yamamoto 1 , Peng Hong Liem 2 , A. Matsumura 3 and Y. Nakagawa 4 1: Japan Atomic Energy Agency, Japan 2: NAIS Co., Inc, Japan 3: University of Tsukuba, Tsukuba, Japan 4: National Children’s Hospital, Japan *E-mail: kumada.hiroaki@jaea.go.jp Abstract IMPROVEMENT OF TREATMENT PLANNING SYSTEM AT JAEA (JCDS) FOR BORON NEUTRON CAPTURE THERAPY. Clinical trials of boron neutron capture therapy (BNCT) are being carried out using the Japan Research Reactor No.4 (JRR-4) in Japan Atomic Energy Agency (JAEA). BNCT is a sort of radiation therapy for an obstinate cancer like a malignant brain tumor. The BNCT clinical trial at JRR-4 has been carried out since 1999. To carry out the clinical trials based on accurate dosimetry, JAEA Computational Dosimetry System (JCDS), a treatment planning system for BNCT, was developed by JAEA. To predict the neutrons and photons behavior around an irradiation field of a patient, JCDS creates a detailed 3D model of a patient using medical images, and then the 3D model is converted into a voxel model. Distributions of neutron flux the corresponding 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 at JRR-4 in October 2003. To enhance the accuracy of dosimetry calculations, JCDS has been improved to create a detailed voxel model consisting of minute voxel cells as small as 2x2x2mm. To calculate the distributions of the fluxes and doses effectively, JCDS has employed transport calculations with “mesh tally” option installed in MCNP version 5. By using the mesh tally option, the computing time can be shortened significantly. Application of the minute voxel calculation combined with mesh tally improves the accuracies of dose evaluation so that an optimum treatment planning for not only the malignant brain tumor but also the head-&-neck cancer can be successfully performed. Keywords: BNCT, JRR-4, treatment planning system, MCNP, dosimetry 1. Introduction BNCT is a sort of radiation therapy for an obstinate cancer such as malignant brain tumors and melanoma. The physical principle of the BNCT was presented in 1936 and its medical application for malignant brain tumors was conducted [1]. In the BNCT procedure, doctors inject a boron compound that builds up selectively in the cancer cells of a patient at first, and subsequently the affected region of the patient is irradiated by a neutron beam from a reactor core. Alpha particles and lithium atoms, which are generated by interactions between neutrons and boron-10 atoms in the cells, destroy the cancer cells selectively. In the last decade, clinical trials of BNCT with epithermal neutron beams have been performed around the world. By using the epithermal neutron beams, the therapeutic range is expanded to deeper regions in the brain than using thermal neutron beams. Clinical trials for BNCT in Japan had been performed using thermal neutron beams at several research reactors: Japan Research Reactor No.2 (JRR-2), Musashi Institute of Technology Reactor (MuITR) and Kyoto University Research Reactor (KUR) [2]. To deliver thermal neutrons to depth in the brain, the BNCT procedure at that time had included craniotomy such as skin flap reopening and bone removal. At present in Japan, the clinical trials for BNCT are performed using mainly epithermal neutron beams at JRR-4 and at KUR. The BNCT clinical trial at JRR-4 was begun since 1999 [3]. First, the BNCT trials in JRR-4, Intra- Operative BNCT (IOBNCT) including the craniotomy were performed with thermal neutron beams. Based on further developments described below and the experiences obtained from the 93 Table of Contents