Optimization of Boron and Neutron Delivery for Neutron Capture Therapy

A number of groups in the United States have received funding that will permit evaluation of the clinical efficacy of the neutron capture therapy (NCT) procedure. Various reactors are being modified to allow the construction of an epithermal neutron beam. At the Brookhaven Medical Research Reactor (BMRR), the patient irradiation facility is being modified to produce an optimized epithermal neutron beam. An 80‐cm‐thick Al‐D₂O mixture (184 g/cm², 25% D₂O by volume) is being installed in the shutter assembly. One‐dimensional calculations indicate that this configuration should provide an epithermal neutron flux density of ∼1 × 10⁹ n/cm²/sec at 3 MW and a concomitant fast neutron dose rate of ∼2 × 10⁻¹¹ rad per epithermal neutron (assuming a homogeneous Al‐D₂O mixture). The actual geometry will be an inhomogeneous array of D₂O and Al layers producing parameters somewhat less favorable than those listed above; experimental verification is in progress. Significant gains have recently been made in selectively targeting B to melanoma with various melanaffinic compounds, including p‐boronophenylalanine, and with boronated porphyrins that may be applicable to a variety of tumors. Neutron capture radiographs have been obtained with the above compounds, and efforts have been made to quantitate boron uptake in growing and quiescent or necrotic regions of tumor via double‐labeling techniques obtained with tritiated thymidine. A correlation between therapeutic efficacy and the ability to deliver boron to viable areas of tumor has been observed.