Distribution of 10B after infusion of Na210B12H11SH into a patient with malignant astrocytoma: implications for boron neutron capture therapy

If a sufficient concentration of the stable isotope 10B is introduced into a neoplasm, radiation therapy can be effected by short-range heavy charged particles from the disintegration of 10B by slow neutrons. Brain tumors were irradiated postoperatively by Hatanaka and co-workers in Japan using a 1 to 2 hour intraarterial infusion of 10B-enriched Na2B12H11SH (Na210B12H11SH) before exposure of the tumor-bearing area of the brain to slow neutrons from a 100 kilowatt nuclear reactor. The clinical outcome of such boron neutron capture therapy has been favorably impressive in some patients, but its efficacy in brain tumors needs improvement. In our study, a terminally ill patient with malignant astrocytoma was infused intravenously with Na210B12H11SH for 25 hours. The postmortem distribution of 10B in unfixed, frozen, tumor-bearing brain and spinal cord tissues was studied by comparing representative cryostat sections of these specimens with neutron-induced heavy charged particle radiographs of the same sections. Preferential accumulation of 10B was observed in the tumor, with relatively little accumulation of 10B in the parenchyma of the central nervous system.

The Monte Carlo simulation of the biological effect of the 10B(n, alpha)7Li reaction in cells and tissue and its implication for boron neutron capture therapy

The energy deposition in the nucleus of cells exposed to the 10B(n, alpha)7Li neutron capture reaction has been calculated and compared to the measured biological effect of this reaction. It was found that a considerable distribution of hit sizes to the nucleus occurs. The comparison of hit size frequency with the observed survival indicates that not every hit, independent of its size, can lead to cell death. This implies the existence of a hit size effectiveness function. The analysis shows that the location of boron relative to the radiation-sensitive volume of the cell is of great importance and that average dose values alone are of limited use for predicting the biological effect of this reaction. Boron accumulating in the cell nucleus is much more efficient in cell killing than the same amount of boron uniformly distributed; its presence in one cell, however, has little effect on its neighboring cells in a tissue. When boron is present on the cell surface of a tissue (as presumably delivered by antibodies), its cell-killing effect is greatly reduced compared to that in uniform distribution. However, in this case much of the dose to one cell comes from neutron capture reactions occurring on the surface of its neighbor cells. These data have implications for the choice of boron carries in neutron capture therapy. The mathematical analysis carried out here is similar to that proposed recently for low-level exposure effects of radiation, taking mutation and/or carcinogenesis as biological effects. The results here show that high-level exposure to high-LET particles (resulting in cell killing) should be treated in an analogous manner.

Boron distribution analysis by alpha-autoradiography

The distribution of the boron-10 compound, Na2 10B12H11SH, which is now in clinical use for boron neutron capture therapy for brain tumors, was studied topographically and quantitatively in rats using neutron-induced alpha-autoradiography. Transplanted intracerebral tumors in Sprague-Dawley rats were used. In the normal brain, only a minute amount of 10B (less than 1 microgram 10B/cm3) was found in the brain parenchyma, except for the infundibulum and area postrema. Boron-10 accumulated in the brain tumors. The tumor-to-blood concentration ratio of 10B increased with time after injection and reached unity 12 hr after injection. The tumor concentration calculated at that time was 18 micrograms 10B/cm3. This study clearly shows that this 10B compound accumulates in the transplanted rat tumors in the brain and that tumor concentration and tumor-to-blood ratio of 10B can provide a sufficient condition for brain tumor treatment.

A prototype epithermal neutron beam for boron neutron capture therapy

An epithermal neutron beam has been designed and tested at the Georgia Institute of Technology's 5-MW Research Reactor. The prototype facility consists of aluminum and sulfur disks in a tangential beam port for fast neutron filtration. A cadmium sheet at the port exit removes the thermal neutrons from the transmitted beam, leaving an intensely epithermal neutron beam spanning five energy decades, each contributing to the flux demanded by boron neutron capture therapy. The thermal neutron flux generated by the incident epithermal neutrons in a polyethylene head phantom peaks at a depth of 3 cm and remains above the incident thermal flux to a 7-cm depth. The beam thus provides the penetration required for treating deep-seated gliomas. Photon contamination in the prototype facility is high, and a number of basic modifications are proposed for reducing it to safer levels.

Boron-neutron capture therapy in relation to immunotherapy

The essential feature of tumour therapy rests upon host-tumour interaction. To achieve therapeutic effects, a prerequisite to immunotherapy is the reduction of tumour cells in the host's body. Such measures should not be immunosuppressive. Cytotoxic chemotherapy is not appropriate in this regard. Supraradical surgery and non-specific radiotherapy are not desirable for preservation of nervous function, if their immunosuppression is not as severe as cytotoxic substances. Boron-neutron capture therapy is a highly specific and least immunosuppressive means of reducing tumour cells of the central nervous system. A brief introductory review of basic research is presented. The interim clinical results are: (i) Treatment of recurrent glioblastoma: Survival extension obtained by neutron capture therapy is 21.9 +/- 7.2 mos in contrast to that obtained by conventional treatments of 6.7 +/- 0.6 mos (p less than 0.001), (Total survival 26.3 +/- 6.7 mos); and (ii) only three patients including two glioblastoma cases were treated with neutron by the same surgeon who, by performing the first tumour operation, had the advantage in topographic knowledge for determining the radiation field. They survived 4, 5, and 6 years in almost fully active conditions. The new Musashi Institute of Technology Reactor Thermal Neutron Therapy Facility and the increased domestic production of boron-10 isotope have enlarged the therapeutic capacity to two dozen patients a year.

Importance of initial management of persons internally contaminated with radionuclides

The first one to three hours following a radiation accident during which internal contamination occurs provide the best and perhaps the only opportunity for preventing uptake of radionuclides. By using chemical manipulation in the GI tract or by hastening the material through the body, absorption can be reduced. Once absorbed, uptake in specific tissues can often be prevented by blocking agents, isotopic dilution or chelating agents. In order to supply prompt treatment, the medical department must have a well-defined action plan based on knowledge of the plant or laboratory operations, the radionuclides used, and medications required.

Electron microscopic study on the response of the normal canine brain to boron-neutron capture therapy

The response of normal cerebral tissue of dogs to boron-neutron capture therapy by the currently available improved method was studied by electron microscopy. Peripheral blood capillaries of the neutron-irradiated area in the left cerebral hemisphere were compared with their counterparts in the shielded and non-irradiated right hemisphere. No ultrastructural changes, as those noted in classical method of boron-neutron irradiation by the improved technique of boron-neutron capture therapy. There was no swelling of endothelial cells, disappearance of cristae of mitochondria, increased pinocytosis, disappearance of ribosomes, enlargement of Golgi apparatus, or increased appearance of endoplasmic reticulum. Basement membrane was not disrupted and was uniform. Pericytes, synaptosomes, and other glial elements remained intact. In contrast to the old clinical trials up to 1961, the renewed boron-neutron capture therapy is regarded not to cause serious damage to the central nervous system.

The therapeutic use of radioactive isotopes

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