Patent Number: 059206012
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to apparatus and methods for delivery of neutron beams for medical therapy. More particularly, it concerns a neutron delivery system with a bimodal energy spectrum that can be used for both fast-neutron therapy and for fast-neutron therapy augmented by boron neutron capture therapy. 2. Background Art Although the prior art for neutron therapy is voluminous, the prior art fails to disclose the bimodal energy spectrum of the present invention. For example, see the following prior art references: U.S. Pat. No. 5,392,319, Feb. 21, 1995, Accelerator-based neutron irradiation, Eggers Phillip E., Dublin, Ohio. U.S. Pat. No. 4,666,651, May 19, 1987, High energy neutron generator, Barjon, Robert, Grenoble, France Breyaat, Genevieve, Brignod, France. U.S. Pat. No. 4,139,777, Feb. 13, 1979, Cyclotron and neutron therapy installation incorporating such a cyclotron, Rautenbach, Willem L., 18 Unie Ave., Stellenbosh, Cape Province, South Africa. U.S. Pat. No. 4,112,306, Sep. 5, 1978, Neutron irradiation therapy machine, Nunan, Craig S., Los Altos Hills, Calif. U.S. Pat. No. 3,781,564, Dec. 25, 1973, NEUTRON BEAM COLLIMATORS, Lundberg, Derek Anthony Hatfield, England. U.S. Pat. No. 3,715,597, Feb. 6, 1973, ROTATABLE NEUTRON THERAPY IRRADIATION APPARATUS, Hoffmann, Ernst-Gunther, Hamburg, Germany, Federal Republic of Meyerhoff, Kaus, Hamburg, Germany, Federal Republic of Offermann, Bernd Peter, Hamburg, Germany, Federal Republic of Barthel, Rolf, Hamburg, Germany, Federal Republic of Germany. Application of neutrons for radiotherapy of cancer has been a subject of considerable clinical and research interest since the discovery of the neutron by Chadwick, in 1932. Fast neutron radiotherapy was first used by Robert Stone in the Lawrence Berkeley Laboratory in 1938. This technology has evolved over the years to the point where it is now a reimbursable modality of choice for inoperable salivary gland tumors, and it is emerging, on the basis of recent research data, as a promising alternate modality for prostate cancer, some lung tumors, and certain other malignancies as well. Neutron capture therapy (NCT), a somewhat different form of neutron-based therapy, was proposed in the mid 1930s and, despite some notable failures in early U.S. trials, has attracted a great deal of renewed research interest lately, due to significant improvements in the relevant technology and radiobiological knowledge. The basic physical processes involved in fast neutron therapy and neutron capture therapy differ in several respects. In fast neutron therapy, neutrons having relatively high energy (approximately 30-50 MeV) are generated by a suitable neutron source and used directly for irradiation of the treatment volume, just as is done with standard photon (x-ray) therapy. Delivery of fast-neutron therapy for cancer is typically accomplished using accelerator based fast neutron sources that generally involve targeting a proton or deuteron beam onto beryllium. Currently available systems employ various types of cyclotron or liner accelerator technology to deliver the necessary proton beam, which impinges on a suitable target, producing neutrons that are subsequently collimated and delivered to the patient via either a fixed beam delivery system, or by a rotating isocentric structure. In neutron capture therapy, a neutron capture agent, which in current practice is boron-10 (yielding Boron NCT, or BNCT) is selectively taken into the malignant tissue following the administration of a suitable boronated pharmaceutical, preferably into the bloodstream of the patient. At an appropriate time after boron administration, the treatment volume is exposed to a field of thermal neutrons produced by application of an external neutron beam. The thermal neutrons interact with the boron-10, which has a very high capture cross section in thermal energy range and which, ideally, is present only in the malignant cells. Each boron-neutron interaction produces an alpha particle and a lithium ion. These highly-energetic charged particles deposit their energy within a geometric volume that is comparable to the size of the malignant cell, leading to a high probability of cell inactivation by direct DNA damage. Because boron is ideally taken up only in the malignant cells, the NCT process offers the possibility of highly selective destruction of malignant tissue, with cellular-level separating of neighboring normal tissue since the neutron sources used for NCT are, themselves, designed to produce a minimal level of damage of normal tissue. When BNCT is administered as a primary therapy, an epithermal-neutron beam (neutrons having energies in the range of 1 eV to 10 keV) is used to produce the required thermal neutron flux at depth, since these somewhat higher-energy neutrons will penetrate deeper into the irradiation volume before thermalizing, yet they are still not of sufficient energy to inflict unacceptable damage to intervening normal tissue. A third form of neutron therapy, which is basically a hybrid that combines the features of fast neutron therapy and NCT is also currently a subject of research interest, and constitutes the field of application where this invention is useful. In this type of radiotherapy, a neutron capture agent is introduced preferentially into the malignant tissue prior to the administration of standard fast neutron therapy. Because a small fraction of the neutrons in fast neutron therapy will be thermalized in the irradiation volume, it is possible to obtain a small incremental absorbed dose from the neutron capture interactions that result. Improved tumor control relative to fast neutron therapy alone using the augmentation concept is clearly promising based on current radiobiological research. However, until now, no NCT augmentation system has been developed that makes a significant improvement over the unaugmented fast neutron therapy. Additionally, prior art fast-neutron therapy systems are largely located only at major research centers due to the fact that they are physically complex, bulky and require high-level operating staffs to maintain. In general these systems are not well suited for wide-spread, practical, clinical deployment. BRIEF SUMMARY AND OBJECTS OF THE INVENTION The present invention provides a potentially compact, user friendly, field-deployable neutron delivery system with dual capabilities for fast neutron therapy alone, or for fast neutron therapy with neutron capture therapy augmentation, with much improved capability for tumor control during neutron beam treatment. It is an object of the present invention to provide improved capability for tumor control during medical therapy through means of superior control of a neutron beam. The present invention is a neutron delivery system that provides improved capability for tumor control by producing a specially tailored neutron beam. The specially tailored neutron beam has a bimodal energy spectrum and provides dramatically enhanced tumor control during medical therapy by allowing neutron therapy to be enhanced with neutron capture therapy. The system includes: a structure for producing a proton beam; at least one target; and a magnet arrangement for directing the proton beam into the at least one target. The target includes layers for producing, when impacted by the proton beam, at least one neutron beam having a bimodal energy spectrum for use with both fast-neutron therapy and boron neutron capture therapy. Finally, the neutron beam passes through a collimator prior to delivery to a patient. Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims.