Dosimetric study of boron neutron capture therapy for malignant mesothelioma

The purpose of this study is to examine the applicability of boron neutron capture therapy (BNCT) to treatment of mesothelioma, a late effect disease of asbestos exposure, with use of imaging findings. CT images of 3 patients were analyzed by dose-volume histogram for dose distribution in the tumor and lung through the SERA (Simulation Environment for Radiotherapy), a therapeutic planning processor only for BNCT. Assumed was the 2-gated irradiation with boronophenylalanine: physical dose (Gy) was converted to photon-equivalent dose (Gy-Eq) with relative and compound biological effectiveness under conditions of the irradiation field of 10B(n, a)7Li, 14N(n, p)14C and fast neutron, of B ratio of tumor (level, 24 ppm)/lung=3.5, and of standard dose D05 (dose delivered to 5% volume of the lung)=5 Gy-Eq. The simulation revealed that the ratio of average doses in the tumor/lung was 5.3, 6.1 and 7.8 in each patient above, indicating that tumors undergo 5-8 times higher dose. The average dose in the lung was found to be 3-4 Gy-Eq, and for assumed 4 fractionated irradiations, tumor can undergo around 80 Gy-Eq or more. The result strongly suggests the usefulness of BNCT as a novel treatment of mesothelioma. (T.I.)