FR2839243A1 - Target used for producing radio-elements, especially fluorine-18 used in positron emission tomographic body imaging, comprises liquid to be irradiated with particle beam enclosed in space defined by inclined foil - Google Patents

Abstract

In a target for the production of radio-elements (I) by irradiation of a liquid with a particle beam, comprising a space for containing the liquid and a first foil defining at least part of the space and crossed by the beam, the first foil has a central region non-perpendicular to the direction of propagation of the beam. An Independent claim is included for a corresponding installation for the production of (I), which comprises a particle accelerator for providing a beam of accelerated particles and at least one target as described above, outside the accelerator and arranged to receive the accelerated particle beam.

Description

i

1 2839243

  The present invention relates to the production of radioactive elements by irradiation

  of a liquid by a beam of particles, for example H + protons.

  It is known to produce 8F by irradiation of water enriched in 8O by a beam of accelerated protons. The gF thus produced can be used to synthesize a substance adminiskable to the human body to, for example, perform PET imaging. US patents 4,752,432, US 5,425,063 and international application WO 00/19787 describe targets for the production of radio elements. The article ISOTOPE PRODUCTION WITH CYCLOTRONS by V. Bechtdold, published in CERN

  ACCELERATOR SCHOOL, CYCLOTRONS, LINACS AND THEIR APPLICATIONS,

  GENEVA 96, following the seminar held in Belgium from April 28 to May 5, 1994, described with reference to FIG. 4, another example of target comprising a space containing

  a liquid intended to be irradiated by a beam of accelerated particles.

  In the case of 8F production, the water enriched in gO is relatively

  expensive to manufacture given the enrichment process used.

  There is therefore a need to reduce the cost of producing

  radio elements, for example from 8F from 8O.

  The invention aims in particular to meet this need.

  It achieves this thanks to a target for the production of at least one radio element by irradiation of a liquid with a beam of particles comprising: - a space capable of containing the liquid to be irradiated by the particle beam, - a first sheet at least partially delimiting said space and intended to be kaversed by the beam, this target can be characterized by the fact that the first sheet has

  a central region not perpendicular to the direction of propagation of the beam.

  Thanks to the invention, the volume of the space containing the liquid to be irradiated can be kept at a relatively low value while having the desired yield for the

  production of the radio-element (s).

  Thus, in the case where the radio-element which is produced is 8F for example, the volume of water enriched in 8O necessary for the production of the quantity of 8F required can

even decreased.

  For a given volume of liquid, the thickness of liquid exposed to the particles can be increased compared to a layer of liquid delimited by two faces perpendicular to the direction of propagation of the particles. For the same thickness of

  liquid exposed to the beam, we can therefore reduce the volume of liquid.

  Furthermore, for a beam of given cross section, the projection of the beam on the inclined sheet is greater than that of the beam on a sheet perpendicular to the direction of propagation of the particles. For the same surface energy density on the sheet, this density not being able to exceed a limit value under penalty of degradation of the sheet, it is therefore possible to increase the intensity of the beam

and / or decrease its cross section.

  A higher intensity makes it possible to increase the speed of production of the radio-element (s), which is all the more advantageous when the half-period of certain elements is very short. The smaller section of the harness makes it possible to further contribute to

  decrease the volume of the liquid intended to produce the radio-element (s).

  The first sheet is advantageously made of a non-alloy material,

especially titanium.

  The target may include a second sheet, located on the side of the first sheet which is opposite the space capable of containing the liquid to be irradiated. This second

  sheet may have a curved part, concave on the side of the first sheet.

  The second sheet may have a central region not perpendicular to

  the direction of propagation of the beam.

  The target may include conduits for injecting hellum onto

  opposite sides of the two sheets, to cool them.

  The target may include a wall defining with the first sheet at least partially the space capable of containing the liquid to be treated, this wall being exposed to the particles of the beam having passed through this liquid. This wall can be electrically insulated to allow a reading of the electric current and it can also

  be cooled by a fluid, for example water.

  The target may include at least one conduit connected to a source of pressurized helium and in communication with the space containing the treated liquid to maintain this

  the latter at a pressure sufficient to prevent the formation of gas bubbles.

  The invention also has for its object and, according to another of its aspects, an installation for producing at least one radio element, comprising: - a particle accelerator capable of delivering a beam of accelerated particles, - at least one target external to the accelerator, arranged so that

  receive the beam of accelerated particles.

  The accelerator may include at least one cyclotron. The installation may also include an optical system in the path of

  particles between the accelerator and the target, configured to widen the beam.

  Such an installation can be used for the production of at least one

  radio element chosen from the following list: gF, i3N, this list not being exhaustive.

  The installation can in particular be used for the production of 8F and the synthesis from this radio-element of a substance which can be administered to the human body,

  especially for PET imaging.

  Another subject of the invention is, according to another of its aspects, a target for the production of at least one radio-element by irradiation of a liquid with a beam of particles, comprising: - a space capable of containing the liquid to be irradiated by the beam of particles, - a sheet delimiting at least partially said space and intended to be crossed by the beam, this target being able to be characterized by the fact that the region of the sheet which is impacted by the incident beam has a shape non-symmetrical in revolution around a beam propagation axis, regardless of the shape or orientation of the region

leaf center.

  Another subject of the invention is, according to another of its aspects, a target for the production of at least one radio-element by irradiation of a liquid with a beam of particles, comprising: - a space capable of containing the liquid to be irradiated by the beam of particles, - a sheet delimiting at least partially said space and intended to be crossed by the beam, this target being able to be characterized by the fact that at least two points of the sheet diametrically opposite with respect to its center lie at different axial positions along the axis of propagation of the beam, whatever the shape or

  the orientation of the central region of the leaf.

  Another subject of the invention, according to another of its aspects, is a target for the production of at least one radio-element by irradiation of a liquid by a beam of particles propagating along an axis, comprising: - a space able to contain the liquid to be irradiated by the particle beam, - a sheet delimiting at least partially said space and intended to be crossed by the beam, this target being able to be characterized by the fact that at least one region of the surface of the sheet, on the side of the incident beam, presents a normal which makes an angle, with the axis of propagation of the beam, greater than or equal to 45, whatever the

  shape or orientation of the central region of the leaf.

  The invention will be better understood on reading the detailed description

  which follows, of nonlimiting examples of implementation, and on examination of the appended drawing, in which: - Figure 1 is a schematic and partial view, in side view, of an installation for the production of '' at least one radio element, - Figure 2 shows in isolation, in schematic and partial axial section, the target of Figure 1, and - Figures 3 and 4 schematically illustrate other examples of

forms for the first sheet.

  The installation 1 represented in FIG. 1 comprises a particle accelerator 10 and at least one target 20 arranged so as to receive a beam of

  accelerated charged particles from the accelerator 10.

  Elements of an optical system 30 can be arranged, as in the example illustrated, on the path of the particle beam between the accelerator 10 and the target

  20, as will be explained below.

  The accelerator 10 can be an isochronous cyclotron of the compact type,

superconductive or not.

  This cyclotron can be associated with a source of ions, for example H- ions, which are accelerated in the cyclotron along a trajectory in the general form of a spiral,

in a manner known per se.

  An electronic peeler, not shown, is placed, in the example under consideration, on the path and H- ions inside the cyclotron to transform these into

  protons H and allow their extraction from cyclotron 10 in the direction of target 20.

  The optical system 30 may comprise one or more magnetic and / or electrostatic lenses and be configured so as to widen the beam to reduce its

surface energy density.

  If we now refer to FIG. 2, we see that the target 20 comprises a first thin sheet or window 21 and a second thin sheet or window 22 each intended to be crossed by the particle beam coming from the cyclotron 10 and is propagating along an X axis.

  In the example illustrated, the sheets 21 and 22 are made of titanium.

  A graphite block 23 defining a circular opening of axis X is placed

  on the path of the beam upstream of the sheets 21 and 22, to serve as a diaphragm.

  The target 20 has a wall 24 downstream of the first sheet 21. This wall is for example constituted by a block of silver. The wall 24 has a face 24a,

  opposite sheet 21, which is substantially parallel to it in the example illustrated.

  The sheet 21 defines, with the wall 24, a space 25 which is intended to be filled with a liquid to be irradiated, for example water enriched in Igo in order to produce 18F. The wall 24 is cooled, on the side opposite to the first sheet 21, by a cooling fluid circulated by a pump not shown, connected to the target by pipes also not shown. The direction of circulation of the

  cooling has been indicated by arrows in FIG. 2.

  A conduit 26, one end of which is in fluid communication with the space 25, is connected at its end end to a source of pressurized helium, making it possible to maintain the liquid contained in the space 25 under sufficient pressure,

  during its irradiation, to avoid the formation of vapor bubbles within it.

  The target 20 also includes, as can be seen in FIG. 2, conduits 27 and 28 making it possible to direct gaseous helium on the opposite faces of the

  first and second sheets 21 and 22, to cool them.

  The first sheet 21 has in the example considered, in accordance with one aspect of the invention, a cenhale region 21a which extends not perpendicular to the axis X. In the example considered, the first sheet 21 is substantially planar and the normal to its central region makes an angle a, measured at the intersection with the X axis, which is close to 45. Of course, it is not beyond the scope of the present invention when the inclination is different, in particular more significant. The inclination a could by

  example, in an example not shown, be greater than or equal to 60.

  The inclination of the sheet 21 makes it possible to increase the path of the accelerated particles within the liquid contained in the space 25, for a given spacing between the sheet 21 and the face 24a of the wall 24. This spacing can for example be just sufficient not to generate the evacuation of the liquid contained in the space 25, while allowing a path of accelerated particles within the liquid sufficient to generate the desired amount of radio element (s). The inclination of the sheet 21 also makes it possible to increase the surface of the sheet crossed by the beam, therefore to use a beam of higher intensity and / or of smaller cross section. A smaller beam can further facilitate cooling of the sheet 21 and reduce the

volume of the treated liquid.

  1S The sheet 22 has, in the example illustrated, a concave curved shape on the side of the sheet 21, which allows it to better resist the pressure difference

  existing on both sides, a relatively high vacuum prevailing upstream of the sheet 22.

  In addition, the sheet 22 has a central region inclined relative to the X axis in order to increase the surface of the sheet exposed to the beam and to benefit from the

advantages outlined above.

  In the example illustrated, the wall 24 is electrically insulated so as to allow a reading of the electric current due to the collection of the incident particles. Such a reading can make it possible to verify the correct functioning of the target during the irradiation.

  The operation of the installation 1 is as follows.

  The ion source associated with cyclotron 10 produces ions, for example H- ions, which are accelerated by the cyclotron and then extracted from it after crossing a

  electronic peeler which transforms them into H + protons.

  The H + protons are directed along the X axis on the target 20, after passing through the optical system 30 which widens the beam and makes it possible to reduce its surface energy density to a value sufficiently low to give the windows 21 and 22 a duration of life compatible with the economic production requirements of the radio element (s). The particles pass through the sheet 21 and reach the liquid contained in

  space 25 where they transform the 8O into 8F.

  The wall 24 is cooled during irradiation and the treated liquid is kept under a pressure sufficient to prevent the formation of vapor bubbles, thanks to the

conduit 26.

  The current collected by the wall 24 is monitored in order to detect any failure. During irradiation, sheets 21 and 22 are cooled by hellum thanks to

at conduits 27 and 28.

  At the end of the irradiation, the cyclotron 10 is stopped and the liquid is evacuated from the space 25 by a system of pipes not shown for the sake of clarity of the drawing and directed for example towards a synthesis device known per se, to synthesize a compound which can be administered to the human body, for example a compound which can be used in the context of PET imaging. Liquid can also be collected and transported to a

remote processing site.

  The fact of having made the sheet 21 of titanium makes it possible to avoid the presence, within the liquid after treatment, of radiotoxic elements having a lifetime

relatively long.

  The invention is not limited to the example which has just been described.

  One can in particular give the sheet 21 a shape other than planar. The shape of the wall, in its region impacted by the incident beam, may or may not be symmetrical with respect to the axis X. Two possibilities are shown, by way of example, in FIGS. 3 and 4,

  among others, shapes for sheet 21.

  In Figure 3, there is partially shown, in isolation, a sheet 21

  substantially conical and which could also be frustoconical.

  We see that the sheet 21 can have at least one region 21b whose normal n makes, with the axis X, an angle a which can be relatively high, whatever

  be the shape and orientation of the central region of the leaf.

  In Figure 4, there is partially shown, in isolation, a sheet 21 not

  flat, showing a drop in its central region.

  In this figure, we can see that the sheet has at least two points diametrically opposite with respect to its center, both spaced by the same distance

  of the X axis and occupying different axial positions along this axis.

  Throughout the description, the expression "comprising a" must be understood

  as being synonymous with "comprising at least one", sanf if the opposite is specified.

Claims (15)

  1. Target (20) for the production of at least one radio-element by irradiation of a liquid with a particle beam, comprising: - a space (25) capable of containing the liquid to be irradiated by the particle beam, - A first sheet (21) at least partially delimiting said space and intended to be crossed by the beam, target characterized in that the first sheet has a region   central (21a) not perpendicular to the direction of propagation (X) of the beam.   2. Target according to claim 1, characterized in that the first   sheet (21) is substantially planar.   3. Target according to one of the preceding claims, characterized in that   that the first sheet (21) is made of a non-alloy material, in particular titanium.   4. Target according to any one of the preceding claims,   characterized in that it comprises a second sheet (22), located on the side of the   first sheet which is opposite the space (25) capable of containing the liquid to be irradiated.   5. Target according to claim 4, characterized in that the second   sheet (22) has a curved part, concave on the side of the first sheet.   6. Target according to any one of claims 4 and 5, characterized by   the fact that the second sheet (22) has a central region not perpendicular to the   direction (X) of beam propagation.   7. Target according to any one of claims 4 to 6, characterized by the   the fact that it has conduits (27, 28) for injecting helium on faces   opposite the two sheets (21, 22).   8. Target according to any one of the preceding claims,   characterized by the fact that it comprises a wall (24) defining with the first sheet at least partially the space (25) capable of containing the liquid to be treated, this wall (24)   being exposed to the particles of the beam having passed through this liquid.   9. Target according to the preceding claim, characterized in that the   wall (24) is electrically insulated to allow reading of the electric current.   10. Target according to any one of the preceding claims,   characterized in that it comprises at least one conduit (26) connected to a source of pressurized helium and in communication with said space (25) to maintain the liquid contained in it at a pressure sufficient for the liquid stay under a liquid phase.   11. Installation (1) for producing at least one radio element, characterized in that it comprises: - a particle accelerator (10) capable of delivering a beam of accelerated particles, - at least one target (20 ) external to the accelerator, as defined in   any one of the preceding claims, arranged to receive the   beam of accelerated particles.   12. Installation according to the preceding claim, characterized in that   the accelerator (10) comprises at least one cyclotron.   13. Installation according to one of claims 11 and 12, characterized by the   that it has an optical system (30) on the path of the particles between   the accelerator (10) and the target (20), configured to widen the beam.   14. Use of an installation as defined in any one of   claims 11 to 13 for the production of at least one radio-element selected from the following list: '8F, 3N.   15. Use of an installation as defined in any of the   Claims 11 to 13 for the production of synthesis and synthesis from this radio   element of a substance which can be administered to the human body, in particular for the purpose of PET imagery.