Neutron Capture Therapy in Oncology

Biophysicist Dr. Doping tells about boric therapy treatments in oncology and radio-surgery.

The idea of neutron capture therapy is to selectively radiation striking only cancer cells, only cancer tissue and healthy not touch. In the case of conventional radiotherapy is done by complicated methods focus beam collimation complex beam accelerator complex movement of the head (a so-called beam intensity modulation). But there is another method. It is connected in order to add to the tumor is a substance that would be the most intensely absorbs radiation that would lead to the release of energy in the required volume of the tumor.

Boric therapy

The idea was expressed even before the war in various countries, including the Soviet Union. But the real practical embodiment it has received after the war, starting with Japan. This method is expensive because it requires, as a rule, use of the nuclear reactor. The method is cumbersome, but for things such as treatment of some brain tumors, it is very promising and is still used.

The most common is the so-called neutron capture therapy boric. It lies in the fact that the isotope boron-10 neutron increased absorbency. He is very good at absorbing neutrons. It has been known nuclear physicists and engineers for the design of nuclear reactors: boron is used in the reactors as an absorber of thermal neutrons, delayed pre-moderated (usually water). And scientists have decided to enter into a tumor drug containing boron. Bohr then absorbs thermal neutrons and splits into the nucleus of lithium-7 and an alpha particle. Both of these particles are charged with a very short run. In this way, a very large amount of energy absorbed in a small volume. This is the idea of such a targeted delivery of energy to the tumor.

Since the neutron capture therapy is expensive, there is usually a limited quantity centers. The discovery of neutron capture therapy centers advisable where there are nuclear reactors and staff able to exploit them. Accommodation reactors for medical needs associated with both the technical and legal challenges. For general purpose reactors - research, energy and so on - are not medical devices. Therefore, for neutron capture therapy is preferred construction of specialized reactors for medical purposes.

Description of the method

The tumor is injected preparation containing boron. This may be a mercapto dodecaborate, it may be some other drugs. But, more importantly, they contain the isotope boron-10, which absorbs thermal neutrons. How to keep the boron-10 in the tumor - is a big problem. To do this, use different methods. The simplest, most straightforward is simply Injecting the drug into the artery that feeds the tumor. You can even inject the drug intratumoral, and then for a while it will be mainly selectively in tumors.

If we want to achieve selective tumor tropism preparation, it is possible to use, for example, complexes that have increased affinity for growth factors that are in the membranes of tumor cells in abundance. Under this approach, the boron-containing composition is placed in the drug complex having an antibody, for example, to some povyshenno protein is expressed in the tumor, for example one of the growth factors. Growth factors of increase expressed in the tumor in the membranes of tumor cells. And then substitute the patient under the beam of thermal neutrons, which goes usually from the reactor and irradiated. Since this method is a spatial standpoint of precision, it is suitable, for example, tumors that in brain, head and neck.

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The effectiveness of the neutron capture therapy

Treatment efficacy is strongly dependent on the type of tumor. Radiation therapy is not indicated for all tumors. This question is more biological than physical and technical. Sometimes even clinicians do not know what the patient, for example, will help radiation therapy, one or another of its kind. There are, of course, the recommendation that radiation therapy is recommended when one or another nosology form of cancer, there is a recommendation that the other nosological form, it is not recommended.

Cases where it is not recommended, we immediately screened out. In cases where it is recommended, it can help a particular patient, and can not help. Our laboratory has developed a program "Oncofinder" which method machine exposure picks up the method of treating cancer, which would be based on the transcriptome (genetic expression) portrait of the tumor, as well as pictures of changes in signaling pathways, it would have been the most effective for a given patient.

Our program "Oncofinder" is commercialized only for chemotherapy, as well as targeted agents. But this same machine learning on signaling pathways and gene expression can be used to distinguish responders and non-responders, and any other method of treating cancer, including radiation therapy on. This means that the method of "Oncofinder" associated with the analysis of signaling pathways and their activation can be applied to analyze and identify responders and nonresponders to radiotherapy. With radiation therapy, the situation is facilitated by the fact that radiotherapy techniques exist although many, but certainly not as much as methods of medical treatment of cancer.

Other methods

There are isotopes which absorb thermal neutrons even better than boron, such as gadolinium-157. But gadolinium - a heavy metal, it is toxic. Gadolinium is difficult to keep in the tumor. If even for boron drugs selective tumor tropism still leaves much to be desired, the gadolinium is satisfactory for the drug to humans has been found. Finding the right treatment for the pharmaceutical form of gadolinium-157 are among the metal nanometer fractions. Such nanoparticles may be able to deliver targeted to the tumor. While such experiments are conducted only in animals and humans using gadolinium neutron capture therapy has not yet been treated.

A cheaper option is to capture radiation therapy photon-capture therapy. When a photon - capture therapy low-energy photon, as a rule, X-ray radiation directed at the tumor, which previously introduced some heavy and so intensely absorbed photon emission element.

What are the advantages of this method? X-ray tube is much cheaper than the reactor and even medical accelerator. Furthermore, for the photon-absorbing products easier to achieve targeted delivery to the tumor. Therefore, the photon-capture therapy as a method of mass much more promising neutron. It is very cheaper than modern accelerators to irradiate cancer tumors photons modulated intensity, with precise focusing of the beam with precision collimation, with a constant dynamic radiation irradiating head during rotation of the accelerator. Besides X-ray tube is much smaller as compared with the accelerator. It may be portable, it can be installed in some distant village, the camp of small nations, in remote areas, and so on - where the situation does not allow even the use of such a massive apparatus as accelerator.

The neutron and photon-capture therapy for this is not the only method. There are, for example, stereotactic radio-surgery for the irradiation of brain tumors, head and neck. In stereotactic radio-surgery patient is irradiated thin beams of photon radiation. This can be a cobalt gamma radiation, as in a gamma knife installation in which hundreds of thin collimated beams. This accelerator may be portable, that is on the robot carrier, and can irradiate the tumor with virtually any position. This ensures precise focusing of energy in a tumor.

Here, in principle, competitors boron neutron capture therapy method. They also use the energy and precision may be less than the reactor. In connection with the development of techniques such as radio-surgery, the role of the reactor boron neutron capture therapy, of course, would be very modest, that is, not by mass, but for certain types of tumors, it is possible and requires development.

This can be, on the other hand, proton therapy, and therapy with heavy ions. There is also the focus of energy, but at the expense of the so-called Bragg peak. The fact that heavy charged particles, what, for example, protons, the lion's share of energy takes place on the last millimeter of the track. Because of this, there is a possibility in the management of energy heavy charged particles emerging from the accelerator (hundreds of MeV, as a rule), change of the depth of penetration of the beam, and hence the depth of energy. The particle goes to the last millimeter with little or no interaction without affecting the surrounding tissue.

In general, almost all methods of radiation therapy, which are developed in the last few decades (20-30 years), aimed at focusing energy within the tumor. Practices, as we see, a lot. From the point of view of physics, and engineering, and biology are completely different methods, and the general aim to increase the precision of the energy within the boundaries of the tumor they have in common.

What would be better is hard to say. For each of the methods has its own niche. But there is one that is most suitable for mass treatment - this is definitely a rotary irradiation intensity modulation at high-energy accelerators with conventional precision dynamic collimators. For head and neck for neuro-oncology promising as neutron capture therapy and radio-surgery; in rare cases even more than neutron capture therapy, may be useful for treatment of heavy charged particles. And for some portable hospitals, we will have a photon capture therapy. Thus, the universal methods (Panacea) have in radiotherapy.