Boron neutron capture therapy (BNCT) for high-grade gliomas of the brain: a cautionary note

Boron neutron capture therapy (BNCT) is a method of treating high-grade gliomas of the brain that involves incorporating 10B into the tumor using appropriate pharmacological agents and then irradiating the tumor with thermal or epithermal neutron beams. To date, over 120 patients have been treated in this manner by Japanese investigators using a thermal neutron beam from a nuclear reactor. Favorable reports on outcome have motivated considerable current research in BNCT. The purpose of this study is to provide an independent analysis of the Japanese data by identifying the subset of patients from the United States who received this treatment in Japan and comparing their outcomes relative to a matched cohort who received conventional therapy in various Radiation Therapy Oncology Group (RTOG) studies.

The principal referral sources of patients to Japan for BNCT were identified and the names of patients sent for treatment obtained. The treating physicians in Japan were also contacted to see if additional patients from the United States had been treated. Either the patients or their next of kin were contacted, and permission was obtained to retrieve medical records including tumor pathology for central review. Prognostic variables according to an analysis of the RTOG brain tumor database by Curran et al. were determined from these records and used to construct a matched cohort of patients treated conventionally.

A total of 14 patients were identified who had traveled to Japan for BNCT treatment between July, 1987 and June, 1994. In the case of one patient (deceased), it was not possible to contact the next of kin. Material was obtained on the other 13 patients and review of the pathology indicated that 1 patient had a central nervous system lymphoma rather than a high-grade glioma. Survival data was analyzed for the other 12 patients on an actuarial basis, and this showed no difference compared to survival data for a matched set of patients constructed according to the classification schema of Curran et al. Median survivals were 10.5 months for both groups; survival at 3 years was 22% for the BNCT group compared to 13% for the conventionally treated group (p = NS). The only long-term survivors in the BNCT group had anaplastic astrocytomas and favorable prognostic criteria (Classes I and II of Curran et al.). The actuarial survival curves for the patients with glioblastoma multiforme (strict histological criteria) who received BNCT and their counterparts who received conventional therapy are virtually superimposable. The respective 2-year survivals are 20 vs. 10% (p = NS). Patterns of failure, toxicity, and analysis of the results according to histology are discussed.

Analysis of patients from the United States who received BNCT treatment in Japan does not support a clinically meaningful improvement in survival attributable to this form of therapy. The implications of this for future BNCT research directions are discussed.