Patent Number: 
Section: description

In FIG. 1 is thus shown a curve over the neutron energy in relation to the flow per lethargic unit both for a known installation curve 1, and for a Studsvik installation having a conventional radiation filter, curve 2, and for a radiation installation according to the invention, curve 8. FIG. 2 shows a group of curves of maximum radiation dose in healthy tissue expressed in Gray Equivalent (Gy equivalent) in relation to probable tumour control or tumour decomposition. The ideal beam for treatment of a brain tumour at the depth of 8 cm (most difficult case) is thereby shown by the graph 3 having the designation BNCTxe2x80x941 which is the optimum curve for radiation treatment of such a brain tumour, which curve 3 has been calculated by means of a computer as known per se. The graphs 4, 5 and 6 of the diagram relate to the results for corresponding cases for the most important of the BNCT beams which are available in the west world. The beams are designated according to the following: The outcome for the beam having a conventional filter in the R2-0 reactor at Studsvik is shown by the graph having the designation S544, curve 7. As evident from the diagram the beam at R2-0 can be expected to give a substantially better treatment result than any of the other beams, corresponding to the presently known technics for radiation treatment of brain tumours, what is observed in that the curve shows that the radiation dose against healthy tissue is substantially less (curve located to the left) than from known installations, curves 4, 5 and 6. The curve 9, marked with S577, corresponds to a treatment in the reactor R2-0 in the case that the reactor is completed by an additional filter, by means of which neutrons are filtered off up to a certain energy the value of which is determined based on the depth at which the tumour is located, whereby consequently the outcome of the radiation can be improved. The technical problem of providing such improvement is to find a filter material which selectively removes neutrons having low energy, up to energies in the area of some few keV without concurrently therewith too much dampening, by spreading processes in the filter material, the intensity of neutrons at the higher energies which are required for the radiation treatment, or without too much affecting the direction spreading of the therapy beam. It is evident that the curve 9 nearly exactly coincides with the calculated optimum radiation curve 3. This is very surprising, and gives a great hope of future successful radiation of deeply located brain tumours, and hopefully healing of brain tumour cancer and also other types of tumours for which the BNCT method is not useful. When treating tumours at less depths in the tissue the treatment result can be optimized in that the energy distribution zone is displaced from the distribution which is the optimum for deeply located tumours (1 keV-40 keV) to less energies. This can be provided in that the neutrons from the reactor are braked by means of a block comprising for instance Al and D2O having various thickness and chosen so that the intensity of neutrons are maximized in the energy area which is optimized for the treatment. For shallow tumours the thickness of the block is adapted so that a solely thermal energy distribution is obtained. For tumours at greater depth in the tissue the thickness of the D2O block is reduced so that the average energy of the neutrons is displaced towards the epithermic area. This method, however, has as an effect that the beam contains a tail of low energetic neutrons of down to thermal energies. This gives a non-desired dose load at and closely inside the surface. Said tail of low energetic beams can be eliminated by using the above mentioned Li6 filter having a thickness which is adapted so that neutrons having the non-desired energies are eliminated from the beam. The said additional filter has to fulfil several different demands for modifying the spectrum. Firstly the absorbing filter material must have such probability of capture and spreading that neutrons having an energy up to the desired keV area are effectively captured at the same time as the spreading of neutrons is minimized. Extensive spreading of neutrons affect the beam unfavourably and affects the direction of the beam. Further the filter must provide an absorption/capture process which is not accompanied by gamma radiation. It has shown that Li6 fulfils said high demands on the filter material. It is further important that the original neutron beam has such intensity that the remaining beam, after having passed the additional filter has sufficient intensity for making a radiation possible within a reasonable period of time. In the above mentioned reactor R2-0 at Studsvik the epithermical (E greater than 0.4 eV) neutron flow originally was 1.4xc3x971010 n/cm2/s at the patient position, and when mounting a lithium plate the neutron flow was 3.6xc3x97109/cm2/s, which is a quite sufficient flow of radiation giving suitable treatment times. In this case the patient was placed at about 75 cm distance from the output surface of the conventional filter Alxe2x80x94AIF3xe2x80x94Bi. In FIG. 3 is diagrammatically, and in a vertical cross section, shown an installation for radiation treatment of a patient 10 having a deeply located brain tumour, for instance at a depth of 8 cm. In the illustrated case the neutron source is a nuclear reactor, in which the core 11 is mounted hanging in the pool 12, and in which the radiation first passes a lead jacket 13 and thereafter a conventional filter 14 which is most clearly shown in FIG. 5. Said conventional filter, which is likewise encapsulated in an about 10 cm thick lead jacket 15 comprises, as seen in the radiation direction, an aluminum plate 16, a relatively thick plate 17 of Alxe2x80x94AIF3, a thin plate of titanium, a thin layer of cadmium and a plate 20 of bismuth. The plates can have the following approximate thickness, which, as mentioned previously, gives a neutron flow at the illustrated installation of 1.4xc3x971010n/cm2/s at a reactor effect of 1 MW: As discussed above it is not appropriate that the beam contains neutrons having very low energy. To this end there is used an additional filter 21 which is mounted between the conventional filter 14 and the output 22 of the radiation tube. Said additional filter 21 also is useful for filtering off radiation having too low energy, for instance energies lower than about 1 keV. A specially useful material for said additional filter 21 has shown to be lithium which is enriched in the isotope Li6. The case illustrated in the drawing relates to radiation of a brain tumour 23 located at a depth of about 8 cm in the brain of a patient. In this case it has shown useful that the lithium filter has a thickness of about 2 cm considering the energy spectrum obtained and the depth of the tumour. For treatment of tumours at other depths than 8 cm, like in the above related case, the thickness of the lithium filter is varied so that a relatively thin lithium filter is used for a more shallowly located tumour and a relatively thicker lithium filter is used for a more deeply located tumour. In FIG. 4 is shown the neutron cross section for capture/absorption and for spreading of Li6. From the figure is evident that the absorption is high for low neutron energies and is reduced to a neglectible value at some tenth keV. The spreading cross section is sufficiently low over the entire energy interval which is of interest for a BNCT beam. Both cross sections show a peak at ≈250 keV, the effect of which is to further improve the quality of the beam by filtering off harmful neutrons at high energies. Clinical experiments with neutron radiation of glioblastoma patients were started in Brookhaven, USA in the year 1951. In the experiments there were used low energetic (thermal) neutrons and boron carrying substances having low selectivity for specific boron deposition/capture in the tumour. For reasons which are easy to understand to-day the results were not successful and the activity was ceased. At the end of the 1960th the experiments were resumed in Japan, now with better selectivity in the boron deposition, but still with beams of thermal neutrons. About 200 patients having glioblastoma have so far been treated. The reporting from the experiments in Japan have indicated a substantial improvement of the therapeutic effects as compared with the radiation therapy with photons which is a routine method all over the world. The Petten group system having the above mentioned radiation designation HFR, also marked in FIG. 2, the Petten Group in the Netherlands, curve 5 of FIG. 2 has, for historical reasons, chosen another boron element (BSH), and there are reasons to expect that the results thereof will be only little successful. The installation in Finland now also is ready to be used, and the first patient radiation treatments are expected to take place during the year 1999. In the Finnish project it is intended to use BPA as the boron carrier. Glioma is the common name for those tumours which are formed by tumour transformation of the support cells of the brain, the so called glia cells. There is a series of types of glioma. The largest type of said types is also the most malignant, namely glioblastoma multiformae. The average surviving time for patients having glioblastoma is about nine months, and there is practically no hope that a patient is healed. The treatment which is used to-day is surgical treatment followed by convention radiation treatment and eventually also treatment with cytostatics. The basic reason for the difficulty of treating glioblastoma is the fact that the tumour cells grow extremely infiltratively. When the tumour is shown for the first time at X-ray examination it can therefore be presupposed that tumour cells already have been spread in the larger part of the brain tissue, even if said cells are present in a very low concentration. This is the explanation for the fact, which has been observed since long, namely that it is quite impossible to heal gliastoma by surgical operation. It is true that radiation treatment has a greater influence on tumour cells than on normal brain cells, but the difference is too little for the radiation treatment to be healing, even if the entire brain should be radiation treated. The same arguments also are valid for cytostatics. One of the difficulties in transferring active substances to the tumour cells is the fact that only some few substances pass the so called blood-brain barrier between the blood vessels and the brain tissue. At the type of BNCT which is used at Brookhaven boron atoms are coupled to the amino acid phenylaianine. Normally phenylalanine passes the blood-brain barrier and is also selectively captured by quickly growing cells. It seems that BPA has the same characteristics. Theoretically it is therefore reasonable to believe hat BPA can be enriched in all the tumour cells of the entire brain volume. The experiments which have been made are supporting said belief. Supposing that a suitable spectrum of neutrons can be obtained it seems that a neutron radiation from both sides of the head might generate a neutron flux in the brain tissue which flux is relatively uniform. An important factor for this development is the filter structure which has been invented according to the Studsvik project. At the survey of the present situation for BNCT at Lund, Sweden, in the summer 1999, it was considered that a radiation should be obtained in the tumour, by a xe2x80x9ctwo beamxe2x80x9d neutron radiation and BPA, corresponding to 30 Gy in a single dose radiation, whereas the radiation in normal brain tissue should be 10 Gy. In this connection it should be reminded that the radiation which is routinely used against metastasis has a lowest dose of 25 Gy. The combination of BPA+the theoretically optimum neutron radiation which can be provided at the Studsvik installation must be considered utterly promising. It is considered quite reasonably to count upon a clear improvement of the therapeutic effect. Further improvements thereafter can be obtained (if considered necessary) by chemical improvements of the carrier molecules.