Induced nuclear reactions: processes – systems – and elements – Epi-thermal reactor structures
Reexamination Certificate
2001-03-09
2004-01-06
Carone, Michael J. (Department: 3641)
Induced nuclear reactions: processes, systems, and elements
Epi-thermal reactor structures
C376S159000, C376S458000, C376S906000, C250S492100, C250S503100, C600S001000
Reexamination Certificate
active
06674829
ABSTRACT:
The present invention generally relates to a radiation apparatus or installation for treatment of various types of cancer tumours, and the invention is more particularly directed to a neutron radiation apparatus/installation for treatment of cancer and of the type which emits neutron beams having a neutron energy of up to 40 keV, and in which the source of neutrons is preferably a nuclear reactor formed with a filter providing a radiation field having preferred low energy neutrons by means of which the tumour is irradiated.
The invention has, in the first place, been developed as the solution of the problem of irradiating tumours in the brain of humans and animals, which tumours have so far been considered extremely difficult to treat. It is, however, obvious that the invention is as well useful for treatment of many other types of tumours and types of cancer.
During the development of the invention there has, in the first place, been used a nuclear set up at Studsvik, Sweden, in the following referred to as R2-0. This is, of course, no limitation of the invention, but many other types of similar reactors can as well be used, like also accelerator based neutron sources, in which the neutrons are produced for example by the known reaction Li
7
(p, n)→Be
7
, in which an accelerated beam of protons (p) is directed to a radiation target comprising the lithium isotope Li
7
, whereby neutrons (n) are emitted resulting in the beryllium isotope Be
7
as the final product.
GENERAL
Shortly after the discovery of the neutron (1932) Locher suggested that neutron beams, in combination with isotopes having a high cross section (high probability) for absorption of neutrons, could be a method of radiation treatment of tumours. The nuclear process which has, in the first place, been discussed to this application is absorption of neutrons in the isotope boron-10
n
+B
10
→B
11
*→Li
7
+He
4
+2.35 MeV.
A boron compound is introduced in the body, whereby the boron compound directs itself to cancer cells and is sucked into same and/or is positioned on the surface of the cancer cell. The reaction is that the B
10
core absorbs/captures a neutron and is transformed to B
11
which spontaneously is decomposed to the nuclear fragments Li
7
and He
4
having a combined kinetic energy of 2.35 MeV (million electron volt). The fragments are electrically charged and therefore strongly ionized along their paths in the surrounding material. The interaction with for instance biologic tissues is so effective that the fragments are completely braked to stop at a distance of 5-10 micrometer (millions of meter), which is the approximate dimension of a human cell. The energy in the molecular cell bond is of the magnitude of some few eV, and the fragments, having an energy of the magnitude of millions of electron volt breaks during its way through the cell millions of molecular bonds, and this is sufficient for destroying the reproductive ability of the cell. If the nuclear process is performed underneath the surface or in the core of a cancer cell the uncontrolled cell splitting is thereby stopped. If a sufficient number of cancer cells are accordingly inactivated the cancer is remedied.
The probability that a cancer cell is knocked out is a product of the probability that there is a B
10
core on or in the cell and the probability that said B
10
cord absorbs/captures a neutron is thereby transferred to B
11
and thereby spontaneously becomes decomposed. The method is named BNCT method (Boron Neutron Capture Therapy). The effectiveness of said method is strongly restricted by the demand that the radiation is not allowed to introduce harmful dose concentrations on healthy tissues, what in turn puts demands both on the boron distribution in and on the tumour cells and the spreading of the neutron field and the energy distribution in the tumour and in healthy tissues.
The problem with deposition of boron or the boron compound in the cancer cell is a question raised in the biochemical research work, where extensive work is being made for providing effective target seeking substances. To-day there is a product on the market (named BPA) which is the amino acid phenylalanine which has been charged with boron atoms, which product issues an excess of boron in the tumour cells as compared with that of healthy tissues by a factor of about three. Other types of boron carrying substances can be used for the same purpose.
The second factor of importance for the therapeutic effect is the spreading of the neutron field in the tissue and the energy distribution of the neutrons in the tumour and in healthy tissues. Said questions belong to the neutron physical research field.
The energy distribution of the neutron beam is of decisive importance for the effect of the therapy in several respects. Firstly the probability that the neutrons are absorbed/captured in the B
10
core, that is the desired therapeutic effect, is strongly depending on the energy. The probability is inverse proportional to the speed “v” of the neutron (so called 1/V cross section) and is therefore a high probability for slow (low energy) neutrons. This means that there is a wish for a radiation field having low energy neutrons at the tumour. A complication is that the dose load on healthy tissues is also depending on the neutron energy. The low energetic components in the radiation field both leads to capture in B
10
in healthy tissues and also to capture in nitrogen and hydrogen cores in the tissues with a resulting non desired emission of reaction fragments and gamma radiation.
For deeply located tumours the situation is further more complicated in that a field of low energetic neutrons is quickly dampened during the passage thereof through the tissue, since this leads to a neutron intensity which is decreasing from the surface of the tissue with a relatively high dose load on the skin and intermediate healthy tissue. The principle method of improving the situation is to perform the radiation by means of neutrons which in the starting position has a relatively high energy. During the passage through the tissue the neutrons are braked by collision with atom nucleus in the tissue (in front of all hydrogen) so that a maximum of slow neutrons in thermal balance with the tissue (thermal neutrons) are built up 2-4 cm from the surface with a tail of low energy neutrons on further distances in the tissue.
Also this method is limited since too high neutron energies lead to a serious dose loads of other type. At a collision of a neutron with a hydrogen core a large part of neutron energy is transferred to the recoiling hydrogen core which, in turn, strongly ionizes (destroys) the tissue. The optimum compromise between said contradictory terms is to execute the radiation with neutrons in an intermediate area of the energy scale, namely by means of so called epithermic neutrons in the area between 1 eV and 40 keV, or preferably between 1 eV and about 20 keV. This can be done in that the neutrons which are produced in the reactor and which has energies in the MeV area are “filtered off” by means of a filter block comprising elements having appropriate neutron physical properties. In the filter there is obtained a selective spreading and retardation of the neutrons, and from the output of the filter there is obtained a radiation beam by neutrons which are relatively evenly distributed in the energy area of 1 eV-40 keV, or preferably 1 eV-20 keV.
This method represents the known technology on which BNCT installations in USA (Brookhaven and MIT) and in Finland (Otaniemi) are based.
BNCT INSTALLATION IN THE R2-0 REACTOR AT STUDSVIK-SWEDEN
The neutron physical requirements for a BNCT installation are far better at the R2-0 reactor than in any existing installation all around the world depending on the specific construction of the Studsvik reactor, which is diagrammatically shown in FIG.
3
and which is to be described in the following. The reason is that the reactor core in the Studsvik reactor R2-0, differing from many other reactors, lacks bot
Carone Michael J.
Keith Jack
Larson & Taylor PLC
Radicon AB
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