Histopathological findings in autopsied glioblastoma patients treated by mixed neutron beam BNCT.

Since 1998, we have introduced a mixed epithermal- and thermal neutron beam for boron neutron capture therapy (BNCT) to improve the neutron beam distribution. Sixteen patients with malignant glioma (glioblastoma, n = 14; anaplastic ependymoma, n = 1; PNET, n = 1) were treated by BNCT in Japan. Of these, 9 died; 3 due to cerebrospinal fluid (CSF) dissemination, 1 each of tumor invasion, meningitis, pneumonia, and unknown causes, and 2 patients died of local recurrence or radiation necrosis. The current postmortem study is comprised of 3 patients with glioblastoma who were treated with BNCT employing an epithermal neutron beam and sodium borocaptate (BSH: Na2B12H11SH). None of the patients manifested local regrowth at the primary site. However, in 2 patients there was CSF dissemination; tumor cells were recognized throughout the subarachnoid space. In the other patient, tumor cells had massively invaded the ipsilateral- and contralateral hemisphere and brain stem from the bottom of the tumor cavity via the corpus callosum and cerebral peduncle. Our findings indicate that BNCT can achieve local control of glioblastoma at the primary site. However, to further improve the clinical outcome after BNCT, steps must be taken to prevent CSF dissemination.