System for generating radioisotopes by bremsstrahlung including a bending converter

Abstract

The invention relates to a system for converting an electron beam into a photon beam, the system comprising: an electron accelerator (1) configured to generate an electron beam (10) of accelerated electrons along an irradiation axis (Z), a scanning unit (2), a focusing unit (3) for forming a focused beam (10f) converging towards a first focus point (Fx) located on the irradiation axis (Z), a conversion unit (4) located between the focusing unit (3) and the first focus point (Fx) and comprising one or more bremsstrahlung converters (4 .1‑4.n), the one or more bremsstrahlung converters being configured to convert the focused beam (10f) into a photon beam (11x), a target holder (5h), the target holder being configured to hold a target (5), characterised in that the one or more bremsstrahlung converters (4.1‑4.n) are curved so that an intersection angle (α) at ​​which the focused beam (10f) intersects each of the one or more bremsstrahlung converters (4.1‑4.n) is between 65° and 115° at all points, preferably between 75° and 105° at all points.

Description

Technical Field

[0001] The present invention relates to an apparatus for producing radioisotopes by irradiating a target with X-rays, which are formed by bremsstrahlung radiation when a converter is bombarded with a high-energy electron beam. In particular, the invention relates to a specific geometry of the converter that reduces the heat generated by the electron beam and allows the use of conventional cooling systems to maintain the converter temperature within an acceptable range. Background Art

[0002] Radioisotopes can be produced by various reactions using charged particles or by utilizing photonuclear reactions (e.g. X-rays). 226 Ra target induced photonuclear reaction) 225 Prepared by the decay of Ra 225 Ac. The energy of the X-rays must be precisely controlled to form the desired isotope, and the energy of the X-rays directly depends on the energy of the electron beam. For example, the energy of the photoirradiation depends on the energy of the irradiation. 226 Ra target can be obtained 223 Ra, 224 Ra and 225 Other examples of radioisotopes commonly used in medical applications include 99m Tc.

[0003] X-rays can be generated by irradiating a converter with a high energy electron beam. The converter is positioned between the high energy electron beam source and the target (in this example, 226 High-energy electron beam sources include electron accelerators such as rhodotrons or linear accelerators. Converters are formed from foil of high-atomic-number metals (such as Ti or Ta). When the electron beam strikes the converter, it decelerates and the released energy is converted into X-ray radiation, which reaches the target and forms the desired radioisotope. This mechanism is known as bremsstrahlung.

[0004] Since only a small portion of the electron beam energy is converted into bremsstrahlung radiation, and the remainder is converted into heat, thermal degradation of the converter is a serious problem. Therefore, the converter must be cooled. Conventional coolers use gases (such as He) or liquids (such as water).

[0005] To enhance converter cooling and / or achieve a wider geometric spread of the photon beam generated by the converter, WO 1999052587 proposes using magnetic scanning coils to scan an electron beam across the converter's scanning area. US 20120025105 combines electron beam scanning with target translation, which is synchronized with the electron beam scanning to ensure that the target is constantly exposed to the full intensity of the bremsstrahlung radiation generated by the converter.

[0006] WO 2017076961 describes a focusing lens for collimating or focusing an electron beam. Collimating the electron beam is useful because a diverging electron beam increases the divergence of the generated photons. This, in turn, requires a larger target to collect the photons. The focusing lens can be formed from magnets and can be a multipole lens, such as a quadrupole lens, a sextupole lens, or an octupole lens.

[0007] Despite the aforementioned improvements, the problem remains of adequately cooling the converter using conventional cooling systems to prevent premature thermal degradation. The present invention addresses the dual problem of preventing premature thermal degradation of the converter using conventional cooling devices while maintaining a focused, high-intensity electron beam, and therefore highly focused X-ray radiation. The solution proposed by the present invention for achieving this dual goal will be explained below. Summary of the Invention

[0008] The invention is defined in the accompanying independent claims. Preferred embodiments are defined in the dependent claims. In particular, the invention relates to a system for generating radioisotopes, the system comprising,

[0009] an electron accelerator configured to generate a beam of accelerated electrons along an irradiation axis (Z),

[0010] a scanning unit configured to deflect the electron beam along a predetermined scanning pattern to form a scanned beam,

[0011] a focusing unit comprising one or more magnets configured to focus the scanned beam in a first irradiation plane (X, Z) towards a first focus point (Fx) located on an irradiation axis (Z) to form a focused beam, wherein the first irradiation plane (X, Z) is defined by the irradiation axis (Z) and a first transverse axis (X), wherein X⊥Z,

[0012] a conversion unit located between the focusing unit (3) and the first focus point (Fx) and comprising one or more Bremsstrahlung converters (4.1-4.n) configured to convert the focused beam into a photon beam,

[0013] a converter cooling system configured to cool one or more bremsstrahlung converters,

[0014] • A target holder configured to hold a target.

[0015] The electron accelerator, the scanning unit, the focusing unit, the conversion unit, and the target holder are all aligned along the irradiation axis (Z) and arranged downstream of each other in this order, where "downstream" is defined relative to the direction of the electron beam. The present system differs from prior art systems in that the one or more bremsstrahlung converters are curved so that the intersection angle (α) at ​​which the focused beam intersects each of the one or more bremsstrahlung converters is between 65° and 115° at all points, preferably between 75° and 105° at all points.

[0016] In a first embodiment, the scanning unit is configured to deflect the electron beam along a predetermined scanning pattern extending along a first transverse axis (X) and a second transverse axis (Y), wherein X⊥Y⊥Z. The focusing unit is configured to further focus the scanning beam in a second irradiation plane (Y, Z) toward a second focus point (Fy) located on the irradiation axis (Z). The second focus point (Fy) may be the same as or different from the first focus point (Fx). The one or more bremsstrahlung converters have an oval cap shape, preferably a spherical cap shape, defined by a first curved cross-section in the first irradiation plane (X, Z) and a second curved cross-section in the second irradiation plane (Y, Z).

[0017] Each of the one or more bremsstrahlung converters has, in a first irradiation plane (X, Z), a first curved cross-section preferably defined by a substantially circular arc having a radius (d1-dn) centered at a first focal point (Fx). A "substantially circular arc" is defined herein as a curved segment in which the radius of curvature does not vary by more than 10% over the length of the curved cross-section. Alternatively or additionally, each of the one or more bremsstrahlung converters has, in a second irradiation plane (Y, Z), a second curved cross-section preferably defined by a substantially circular arc having a radius (d1-dn) centered at a second focal point (Fy). Preferably, the second focal point (Fy) is the same as the first focal point (Fx) (i.e., Fx=Fy).

[0018] In a second embodiment, the scanning unit is configured to deviate the electron beam along a predetermined scanning pattern extending only along the first transverse axis (X). The one or more bremsstrahlung converters are in the shape of a partial cylinder defined by a curved cross section in a first transverse plane (X, Z) and a generatrix extending along a second transverse axis (Y), wherein X⊥Y⊥Z. Each of the one or more bremsstrahlung converters has, in the first irradiation plane (X, Z), a first curved cross section preferably defined by a substantially circular arc with a radius (d1-dn) centered at the first focus point (Fx).

[0019] The focusing unit can be configured to form a focused beam, wherein a focusing half-angle (β) formed by the focused beam at a first focusing point (Fx) and the irradiation axis (Z) on a first irradiation plane (X, Z) is between 20° and 55°, preferably between 30° and 45°.

[0020] The one or more bremsstrahlung converters may be made of tantalum (Ta), tungsten (W), or titanium (Ti). The thickness (L90) of each of the one or more bremsstrahlung converters, measured along the radius of curvature, preferably does not exceed 3 mm, preferably, the thickness (L90) is between 0.2 mm and 2.5 mm, more preferably between 0.5 mm and 1.5 mm. Further preferably, the nth bremsstrahlung converter closest to the target holder has a greater thickness (L90) than the first bremsstrahlung converter closest to the focusing unit.

[0021] The conversion unit may comprise 1 to n bremsstrahlung converters separated from each other by cooling channels, wherein n is between 2 and 8, preferably between 3 and 5. The converter cooling system may comprise forced cooling of a gas or liquid flowing through the channels.

[0022] The present invention also relates to a method for producing radioisotopes by irradiating a target with X-rays, the method comprising:

[0023] providing a system as defined above,

[0024] Loading the target onto the target holder,

[0025] Scanning and focusing the accelerated electron beam onto the conversion unit to generate X-rays,

[0026] The target is irradiated with the X-rays thus generated.

[0027] The target can be selected from one of the following: 225 Ac's 226 Ra, or used to form 99m Tc 100 Mo, or used to generate 187 Re 186 W, or used to form 131 I 134 Xe, or for generating 67 Cu's 68 Zn. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more fully understand the essence of the present invention, reference is made to the following detailed description in conjunction with the accompanying drawings, in which:

[0029] Figure 1 (a): shows a side view of a system according to the present invention.

[0030] FIG1( b ) shows a perspective view of a first embodiment of a system according to the present invention.

[0031] FIG. 1( c ) shows a perspective view of a second embodiment of a system according to the present invention.

[0032] Figure 2 : A view showing a scanning unit and a focusing unit according to the present invention.

[0033] Figure 3 : shows an example of a conversion unit according to the present invention.

[0034] FIG. 4( a ): shows the maximum distance (L α ) that an electron beam travels through a straight sheet bremsstrahlung converter according to the prior art, where α=β+90°.

[0035] FIG4( b ): shows the maximum distance (Lα) that an electron beam passes through the curved sheet bremsstrahlung converter according to the present invention, where 65°≤α≤115°.

[0036] FIG4( c ) shows the maximum distance (L90) that an electron beam travels through a curved sheet bremsstrahlung converter according to a preferred embodiment of the present invention, where α=90°.

[0037] Figure 4(d): plots the normalized maximum distance (Lα / L90) of an electron beam through a curved sheet bremsstrahlung converter according to the invention as a function of the angle α; the lowest value of Lα is L90 at α = 90°.

[0038] FIG. 5( a ): shows a graph representing the height (hi) of a scanned beam across a scan area of ​​a direct-bremsstrahlung converter according to the prior art.

[0039] Figure 5(b): shows a graph representing the height (ci) of the scanned beam across the scan area of ​​the curved bremsstrahlung converter according to the present invention.

[0040] FIG. 5( c ): Comparison of the height of the scanned beam through a Bremsstrahlung converter according to the prior art ( hi ) and through a Bremsstrahlung converter according to the present invention ( ci ).

[0041] Figure 5(d): The height ratio (c1 / h1) of the scanned beam passing through the Bremsstrahlung converter is plotted as a function of the focusing half-angle (β). DETAILED DESCRIPTION

[0042] The present invention relates to a system for producing radioisotopes by converting an electron beam into a photon beam and irradiating a target (5) with the photon beam. The system comprises an electron accelerator (1) configured to generate an electron beam (10) of accelerated electrons along an irradiation axis (Z). A scanning unit (2) is inserted downstream of the electron accelerator along the irradiation axis (Z). The scanning unit (2) is configured to deviate the electron beam (10) along a predetermined scanning pattern to form a scanning beam (10s). A focusing unit (3) is inserted downstream of the scanning unit along the irradiation axis (Z). The focusing unit comprises one or more magnets (3m) configured to focus the scanning beam (10s) on a first irradiation plane (X, Z) toward a first focusing point (Fx) located on the irradiation axis (Z) to form a focused beam (10f), wherein the first irradiation plane (X, Z) is defined by the irradiation axis (Z) and a first transverse axis (X), wherein X⊥Z.

[0043] The conversion unit (4) is located between the focusing unit (3) and the first focus point (Fx). The conversion unit comprises one or more bremsstrahlung converters (4.1-4.n), which are configured to convert the focused beam (10f) into a photon beam (11x). The conversion unit is equipped with a converter cooling system (4c), which is configured to cool the one or more bremsstrahlung converters (4.1-4.n).

[0044] The target holder (5h) is configured to hold a target (5) exposed at a first focus point (Fx). The target holder is equipped with a target cooling unit (5c) configured to cool the target (5) when the target (5) is held in the target holder (5h).

[0045] The electron accelerator (1), the scanning unit (2), the focusing unit (3), the conversion unit (4) and the target holder (5h) are all aligned along the irradiation axis (Z) and are arranged downstream of each other in this order, where "downstream" is defined relative to the electron beam direction.

[0046] The gist of the invention is that one or more bremsstrahlung converters (4.1-4.n) are curved so that the intersection angle (α) at ​​which the focused beam (10f) intersects each of the one or more bremsstrahlung converters (4.1-4.n) is between 65° and 115° at all points, preferably between 75° and 105° at all points, more preferably the intersection angle (α) is equal to 90°±5°.

[0047] Electron accelerator (1)

[0048] Electron accelerators are well known in the art. The present invention is not limited to any particular type of electron accelerator, as long as it is capable of generating an electron beam (10) having an energy between 10 MeV and 40 MeV, preferably between 15 MeV and 30 MeV, and preferably between 20 MeV and 25 MeV. The diameter of the electron beam (10) may be less than 10 mm. The electron accelerator may be, for example, a linear particle accelerator (e.g., a linac) or a petal-shaped accelerator (e.g., a rhodotron).

[0049] Scanning unit (2)

[0050] Scanning units are well known in the art. The present invention is not limited to any particular type of scanning unit, as long as it is capable of scanning an electron beam (10) along a predetermined scanning pattern to form a scanning beam (10s). Upon impacting a bremsstrahlung converter, only a small portion of the electron beam energy is converted into X-ray energy. The remaining energy is dissipated as heat. By scanning the electron beam onto the converter, a flat beam distribution is produced over the entire surface of the converter, and the concentration of beam power and heat generation in a small scanning area of ​​the converter is reduced.

[0051] The scanning unit (2) may be equipped with a scanning magnetic coil (2m) in a lateral direction of the electron beam (10). The scanning magnetic coil may be configured to cause the electron beam to linearly scan along a first transverse direction (X) as shown in FIG1(c). Alternatively, the scanning magnetic coil may be configured to cause the electron beam to scan across a scanning area along a first transverse direction and a second transverse direction (X, Y) as shown in FIG1(b).

[0052] In a first embodiment, the scanning unit (2) is configured to deviate the electron beam (10) along a predetermined scanning pattern extending only along the first transverse axis (X). Alternatively, in a second embodiment, the scanning unit (2) is configured to deviate the electron beam (10) along a predetermined scanning pattern extending along the first transverse axis (X) and the second transverse axis (Y), wherein X⊥Y⊥Z.

[0053] As mentioned above, by scanning the electron beam onto the converter in the first and optionally the second transverse direction, cooling of the converter is facilitated. However, this results in the photon beam thus formed having a wider geometric spread. In some cases, when a large target is available, this may be an advantage. However, when target material is scarce and a small target must be used (e.g. for 226 Ra), the wide geometric spread of X-rays may become inconvenient. For this reason, it has been proposed in the art to use a focusing unit to converge the scanning beam (10s) to focus the beam onto the converter via a focusing magnetic coil (3m).

[0054] Focusing unit (3)

[0055] For targets of smaller sizes, the scanning beam (10s) cannot be used effectively in this way. This is because the photon beam (11x) formed by the interaction of the scanning electron beam with the conversion unit (4) also spreads out. For targets of small sizes, it is necessary to refocus the scanning beam (10s) or the photon beam (11x). For example, focusing of the photon beam (11x) is described in WO 2012022491. In the present invention, the system includes a focusing unit (3) located upstream of the conversion unit (4) for focusing the scanning beam (10s) to form a focused beam (10f).

[0056] The focusing unit (3) is configured to focus the scanning beam (10s) on a first irradiation plane (X, Z) toward a first focus point (Fx) located on an irradiation axis (Z) to form a focused beam (10f). The first irradiation plane (X, Z) is defined by the irradiation axis (Z) and a first transverse axis (X), where X⊥Z. Focusing units of this type are well known in the art. The present invention is not limited to any particular type of focusing unit (3), as long as it is capable of focusing the scanning beam (10s) toward the first focus point (Fx) to form a focused beam (10f) as the scanning beam (10s) scans. For smaller targets, a correspondingly smaller focus point (Fx) is required.

[0057] like Figure 2 As shown, the focusing unit (3) of the scanning beam (10s) can include a lens formed by a focusing magnetic coil (3m), which forms a multipole lens, such as a quadrupole lens, a sextupole lens or an octupole lens. The focused beam (10f) thus formed still scans in the first transverse direction and optionally in the second transverse direction (X, Y), but as shown in Figure 5(b), the focused beam converges from all points of the scanning pattern towards the first focus point (Fx). Since the converter is located between the focusing unit (3) and the first focus point (Fx), the focused beam (10f) scans over the scanning area of ​​the converter unit (4), so that the energy of the focused beam is distributed over a larger scanning area.

[0058] In an embodiment wherein the scanning unit (2) is configured to deviate the electron beam (10) along a predetermined scanning pattern extending along a first transverse axis (X) and a second transverse axis (Y), the focusing unit (3) may be configured to further focus the scanned beam (10s) in a second irradiation plane (Y, Z) towards a second focusing point (Fy) located on the irradiation axis (Z). The second focusing point (Fy) may be the same as or different from the first focusing point (Fx).

[0059] Figure 3 、 Figure 4(a) to Figure 4(c) as well as Figure 5(a) to Figure 5(c)The focusing half-angle (β) formed between the irradiation axis (Z) and the outer envelope of the electron beam thus focused at the first focusing point (Fx) shown in , may be between 20° and 55°, preferably between 30° and 45°. If the scanning beam (10s) is scanned in the first and second transverse directions (X, Y), the focusing half-angle (β) formed at the second focusing point (Fy) may be comprised in the same range as defined above if the second focusing point (Fy) is different from the first focusing point (Fx).

[0060] Conversion unit (4)

[0061] As shown in Figure 5(a), the conversion unit is conventionally formed by a plurality of Bremsstrahlung converters (4.1-4.n) in the form of flat sheets of high atomic number metal aligned one after another along the irradiation axis (Z) and separated from each other by cooling channels. There are two main problems with arranging such a conversion unit downstream of the focusing unit (3).

[0062] First, as shown in FIG4(a), it can be seen that the outermost electrons in the focused beam (10f) intersect the Bremsstrahlung converter sheet (4.1) at an intersection angle (α) greater than 90°, while electrons traveling along the irradiation axis (Z) intersect the Bremsstrahlung converter sheet (4.1) at an intersection angle (α) of 90°. As can be clearly seen in FIG4(a) and plotted in FIG4(d), the length (Lα) that an electron travels through the Bremsstrahlung material depends largely on the intersection angle (α), with a minimum length (L90) at an intersection angle α = 90° (see FIG4(d)). This means that the outermost electrons, which travel a longer path (Lα) through the Bremsstrahlung material, release more energy, and therefore more heat, than electrons closer to the irradiation axis (Z) traveling at a path length close to or equal to L90. This is problematic because there are temperature gradients across the scanned area of ​​the bremsstrahlung converter and because the outermost electrons, which release more energy at the first bremsstrahlung sheet, have less energy to the following sheets than the innermost electrons, which travel closer to the irradiation axis (Z).

[0063] Secondly, as shown in Figures 5(a), 5(c), and 5(d), when the Bremsstrahlung sheets are flat, the scan area of ​​the focused beam (10f) passing through each Bremsstrahlung sheet is smaller than when the Bremsstrahlung sheets are curved. Figure 5 shows a side view or projection onto a plane (X, Z), and the two-dimensional area in the 3D system is simplified to the one-dimensional lengths (hi, ci, where i = 1 to n) in the 2D projection of Figure 5. Therefore, when referring to the lengths hi or ci, the term "area" is used to make the reader mentally multiply the lengths hi and ci by the corresponding lengths in the second transverse direction (Y) to obtain a value in units of .

[0064] In FIG5( a ), the scan area of ​​the focused electron beam (10 f ) through the bremsstrahlung sheet is represented by a length (hi , i=1 to n). Referring to FIG5( c ), the length hi can be calculated based on the focus half-angle (β) according to hi=di x sinβ, where di is the distance separating the i-th bremsstrahlung converter (4.i) from the first focus point (Fx), as measured along the irradiation axis (Z). Increasing the scan area of ​​the focused beam (10 f ) through the bremsstrahlung sheet can be advantageous, particularly if a large number (n) of bremsstrahlung sheets are used, because the scan area decreases after each sheet, thereby increasing the concentration of the beam energy on a smaller scan area.

[0065] The present invention proposes replacing the flat sheet-shaped bremsstrahlung converters used so far in the art with curved bremsstrahlung converters (4.1-4.n) in the form of curved sheets, such that the intersection angle (α) at ​​which the focused beam (10f) intersects each of the one or more bremsstrahlung converters is between 65° and 115° at all points, preferably between 75° and 105° at all points. Preferably, the intersection angle is 90°. The 90° intersection angle at all points of the conversion unit (4) can be achieved by using bremsstrahlung converters in the form of sheets with a single or optionally double curvature radius (di), where the curvature radius is defined as the distance separating the curved sheet from the first and optionally second focus points (Fx, Fy). If the first and second focus points are identical, the geometry of the bremsstrahlung sheet is a spherical cap with radius (di). This simple solution solves the two problems mentioned above by obtaining the following:

[0066] More uniform heat distribution over the scan area of ​​the focused beam (10f) across the Bremsstrahlung sheet, and

[0067] • The focused beam (10f) passes through a larger scan area of ​​the Bremsstrahlung sheet.

[0068] More even heat distribution

[0069] As shown in Figures 4(b) and 4(c), by locally tilting the Bremsstrahlung sheet by an angle γ relative to the irradiation direction parallel to the irradiation axis (Z), the intersection angle (α) can be made closer to or even equal to 90°. With a sufficiently curved Bremsstrahlung sheet, the intersection angle (α) can be reduced to between 65° and 115° at all points, preferably to between 75° and 105° at all points. Referring to Figure 4(d), it can be seen that within the range of intersection angles (α) between 65° and 115° at all points, represented by the lightly shaded area, the normalized thickness (Lα / L90=1 / sin α) can vary by up to approximately 10% When the intersection angle (α) range is reduced to between 75° and 105° (indicated by the dark shaded area in FIG4( d )), the normalized thickness (Lα / L90) for any two electrons of the focused beam (10 f) varies by less than 4% (Lα / L90=1.04). If the intersection angle α=90° at all points, the normalized thickness (Lα / L90=1) is constant for all electrons of the focused beam, and the heat energy transferred to the bremsstrahlung converters (4.1-4.i) is evenly distributed over the entire scanning area of ​​the focused beam (10 f) across the conversion unit (4), without localized areas of higher temperature.

[0070] In contrast, as shown in FIG4( a ), the focused beam ( 10 f ) passes through the Bremsstrahlung flat sheet at a cut-off angle of, for example, α = 135°, corresponding to a focusing half-angle β = α-90° = 45°. The normalized thickness variation of the flat sheet passed by the focused beam exceeds 40% (Lα / L90 = 1.4 in FIG4( d )), and a thermal gradient of comparable proportion is obtained over the scanning area of ​​the flat sheet passed by the focused beam ( 10 f ).

[0071] The use of curved bremsstrahlung converters (4.1-4.n) results in a focused beam (10f) intersecting each of the one or more bremsstrahlung converters (4.1-4.n) at an angle (α) between 65° and 115° at all points, which significantly facilitates homogenization of the heat generated by the interaction with the focused beam over the scan area of ​​the bremsstrahlung converter. Compared to a flat sheet, the curved sheet makes cooling the converter unit easier, and conventional cooling systems (4c) can be successfully used.

[0072] Larger scanning area

[0073] Referring to Figures 5(a) and 5(c), it can be seen that the scanning area represented by the height (hi) of a conversion unit formed from a flat sheet can be characterized by the value hi = di x sin β, while the scanning area represented by the curved height (ci) of a conversion unit formed from a curved sheet having a radius (di) can be characterized by the value ci = di x β. The height ratio (ci / hi) of the curved height (ci) according to the present invention to the height (hi) according to the prior art can be expressed as ci / hi = β / sin β. Figure 5(d) plots the height ratio (ci / hi) as a function of the focus half-angle (β). It can be seen that for a focus half-angle of, for example, β = 45°, the curved bremsstrahlung converter has a scanning area (ci) that is 10% larger than that of the flat sheet. For a focus half-angle of β = 50°, the scanning area is approximately 15%. This increase in scanning area, by utilizing a curved bremsstrahlung converter, allows the focused beam energy to be distributed over a larger scanning area compared to a flat bremsstrahlung converter. Therefore, the heat generated by the interaction of the focused beam with the scanning area of ​​the conversion unit is correspondingly reduced, thereby further facilitating the cooling of the conversion unit (4).

[0074] Geometry of the Bremsstrahlung converter (4.1-4.n)

[0075] One or more bremsstrahlung converters (4.1-4.n) may be in the shape of a partial cylinder defined by a curved cross section in a first transverse plane (X, Z) and a generatrix extending along a second transverse axis (Y), wherein X⊥Y⊥Z. This geometry is preferred in cases where the scanning unit (2) is configured to deflect the electron beam (10) along a predetermined scanning pattern extending only along the first transverse axis (X). This geometry is also preferred in cases where the target (5) has a length defining an elongated shape and the scanning beam does not need to be focused on a plane comprising the length of the elongated target. A converter unit (4) of this type is illustrated in FIG1(c).

[0076] In an alternative embodiment, one or more bremsstrahlung converters (4.1-4.n) are in the shape of an oval cap, preferably a spherical cap, defined by a first curved cross section in a first irradiation plane (X, Z) and a second curved cross section in a second irradiation plane (Y, Z). This type of converter unit is illustrated in FIG1( b) and is particularly suitable for the case where the scanning unit (2) is configured to deflect the electron beam (10) along a predetermined scanning pattern extending along a first transverse axis (X) and a second transverse axis (Y), wherein X⊥Y⊥Z, and the focusing unit (3) is configured to focus the scanned beam (10s) in the second irradiation plane (Y, Z) towards a second focus point (Fy) located on the irradiation axis (Z), wherein the second focus point (Fy) may be the same as or different from the first focus point (Fx). In a preferred embodiment, the first and second focus points (Fx, Fy) are the same focus point (i.e., Fx=Fy).

[0077] In both embodiments (i.e. single curvature or double curvature), it is preferred that the radius of curvature of the curved section is constant, i.e. defining a circular arc or a spherical cap, respectively. The radius of curvature is preferably close to the distance (di) separating the Bremsstrahlung converter (4.1-4.n) from the first focus point (Fx).

[0078] In a preferred embodiment, each of the one or more bremsstrahlung converters (4.1-4.n) has a first curved cross-section in a first irradiation plane (X, Z) defined by a substantially circular arc with a radius (d1-dn) centered at a first focus point (Fx). A "substantially circular arc" is defined herein as a curved segment in which the radius of curvature does not vary by more than 10% over the length of the curved arc. With this geometry, the focused beam (10h) reaches the bremsstrahlung converter along the first irradiation plane (X, Z) at an intersection angle α=90°.

[0079] In a further preferred embodiment, each of the one or more bremsstrahlung converters (4.1-4.n) has, in the second irradiation plane (Y, Z), a second curved cross-section defined by a substantially circular arc with a radius (d1-dn) centered at a second focal point (Fy). Preferably, the second focal point (Fy) is identical to the first focal point (Fx) (i.e., Fx=Fy), thereby defining a spherical cap geometry centered at a single focal point (Fx=Fy).

[0080] like Figure 3As shown, the conversion unit (4) comprises 1 to n bremsstrahlung converters (4.1-4.n) separated from each other by cooling channels, wherein n is between 2 and 8, preferably between 3 and 5. The converter cooling system (4c) may comprise gas or liquid forced cooling, wherein a cooling fluid flows through the cooling channels to recover heat from the bremsstrahlung converters generated by interaction with the focused beam (10f). This configuration defines what is referred to herein as a "conventional cooling system", which is well known to those skilled in the art.

[0081] The thickness (L90) of each of the one or more Bremsstrahlung converters (4.1-4.n) measured along the radius of curvature does not exceed 3 mm, preferably the thickness (L90) is between 0.2 mm and 2.5 mm, more preferably between 0.5 mm and 1.5 mm. The radius of curvature at a point of the Bremsstrahlung converter is defined as the radius of a circle that touches the Bremsstrahlung converter at that point and has the same tangent and curvature at that point. Thus, the radius of curvature is orthogonal to the tangent of the Bremsstrahlung converter at that point. This is Figure 4(a) to Figure 4(c) The thickness (L90) is also the shortest straight line through the Bremsstrahlung converter from one surface to the opposite surface.

[0082] In a preferred embodiment, the nth bremsstrahlung converter (4.n) closest to the target holder (5h) in a sequence of n bremsstrahlung converters has a greater thickness (L90) than the first bremsstrahlung converter (4.1) closest to the focusing unit (3). Preferably, each bremsstrahlung converter (4.i) in the sequence is thicker than the adjacent bremsstrahlung converter (4.(i-1)) located upstream, i.e., L90(4.i)>L90(4.(i-1)). Since the scanning area of ​​a bremsstrahlung converter decreases as the bremsstrahlung converter gets closer to the first focus point (Fx), increasing the thickness of the bremsstrahlung converters located downstream in the sequence allows for homogenizing the amount of interaction of the bremsstrahlung converter material with the focused beam (10f). In this way, all bremsstrahlung converters contribute equally to the generation of X-rays. The heat generated by the interaction and which must be dissipated is also distributed more evenly between the individual bremsstrahlung converters of the conversion unit (4), thereby facilitating its cooling.

[0083] The 1 to n bremsstrahlung converters (4.1-4.n) may be made of tantalum (Ta) or tungsten (W) or titanium (Ti).

[0084] Target (5) and target holder (5H)

[0085] Due to the use of the focusing unit, the system of the present invention is particularly suitable for targets (5) of small size. The target (5) can be 226Ra, which is used to generate the 225 Other examples of targets that can be used with the system of the present invention to form diagnostic imaging isotopes include: 99m Tc 100 Mo target, or used to generate 187 Re 186 W target, or for forming 131 I 134 Xe, or for generating 67 Cu's 68 Zn etc.

[0086] Since the transmutation reaction caused by the interaction of the X-rays (11x) with the target generates heat, a target cooling system (5c) is provided, which is configured to cool the target (5) when it is held in the target holder (5h). Similar to the converter cooling system (4c) described above, the target cooling system (5c) can include gas or liquid forced cooling, in which a refrigerant fluid flows through a cooling channel in thermal contact with the target (5). It is of course important to keep the temperature of the target (5) below the degradation temperature.

[0087] If the first and second focal points are identical (i.e., Fx=Fy), and the X-rays thus generated by the conversion unit (4) converge towards a small convergence area around the focal point (Fx), the sample holder can be configured to move the target (5) so that the focal point (which is stationary) scans a larger area of ​​the target. This is particularly relevant in the case of large target sizes, since the exposed area of ​​the target is larger than the convergence area of ​​the X-rays, so that transmutation can occur over a larger area / volume of the target than if the target remained stationary.

[0088] Methods for producing radioisotopes

[0089] The system of the present invention can be used in a method for generating radioisotopes by irradiating a target with X-rays. The method comprises providing the system as described above. After loading a target (5) onto a target holder (5h), an accelerated electron beam is scanned and focused onto a conversion unit (4) to generate X-rays, thereby irradiating the target with the X-rays thus generated.

[0090] The target can be, for example, to generate 225 Ac's 226 Ra, or used to form 99m Tc 100 Mo target, or used to generate 187 Re 186 W target, or for forming 131 I 134 Xe, or for generating 67 Cu's 68 Zn etc.

[0091]

[0092]

Claims

1. A system for generating radioisotopes, the system comprising: • an electron accelerator (1) configured to generate an electron beam (10) of accelerated electrons along an irradiation axis Z, • a scanning unit (2) configured to deflect the electron beam (10) along a predetermined scanning pattern to form a scanning beam (10s), • a focusing unit (3) comprising one or more magnets configured to focus the scanned beam (10s) towards a first focus point (Fx) located on the irradiation axis Z in a first irradiation plane (X, Z) to form a focused beam (10f), wherein the first irradiation plane (X, Z) is defined by the irradiation axis Z and a first transverse axis X, wherein X⊥Z, • a conversion unit (4) located between the focusing unit (3) and the first focus point (Fx) and comprising one or more Bremsstrahlung converters (4.1-4.n) configured to convert the focused beam (10f) into a photon beam (11x), • a converter cooling system (4c), said converter cooling system being configured to cool said one or more bremsstrahlung converters (4.1-4.n), • a target holder (5h) configured to hold the target (5), wherein the electron accelerator (1), the scanning unit (2), the focusing unit (3), the conversion unit (4) and the target holder (5h) are all aligned along the irradiation axis Z and are arranged downstream of each other in this order, wherein "downstream" is defined relative to the direction of the electron beam, The invention is characterized in that the one or more bremsstrahlung converters (4.1-4.n) are curved so that the intersection angle ( ) is between 65° and 115° at all points.

2. The system according to claim 1, wherein: • the scanning unit (2) is configured to deviate the electron beam (10) along the following predetermined scanning pattern: the predetermined scanning pattern extends along the first transverse axis X and the second transverse axis Y, wherein X⊥Y⊥Z, • the focusing unit (3) is configured to focus the scanning beam (10s) also in a second irradiation plane (Y, Z) towards a second focus point (Fy) located on the irradiation axis Z, wherein the second focus point (Fy) can be the same as or different from the first focus point (Fx), and • The one or more bremsstrahlung converters (4.1-4.n) have an oval hat shape defined by a first curved cross section in the first irradiation plane (X, Z) and a second curved cross section in the second irradiation plane (Y, Z).

3. The system according to claim 1, wherein: • the scanning unit (2) is configured to deviate the electron beam (10) along a predetermined scanning pattern extending only along the first transverse axis X, and • The one or more bremsstrahlung converters (4.1-4.n) are in the shape of a partial cylinder defined by a curved section in the first irradiation plane (X, Z) and a generatrix extending along a second transverse axis Y, wherein X⊥Y⊥Z.

4. The system according to any one of claims 1 to 3, wherein: The focusing unit (3) is configured to form the focused beam (10f), wherein the focused beam forms a focusing half-angle ( ) is between 20° and 55°.

5. The system according to any one of claims 1 to 3, wherein: Each of the one or more bremsstrahlung converters (4.1-4.n) has, in the first irradiation plane (X, Z), a first curved cross-section defined by a substantially circular arc with a radius (d1-dn) centered at the first focus point (Fx), wherein a "substantially circular arc" is defined as a curved segment having a radius of curvature that does not vary by more than 10% over the length of the curved cross-section.

6. The system according to claim 2, wherein: Each of the one or more bremsstrahlung converters (4.1-4.n) has, in the second irradiation plane (Y, Z), a second curved cross-section defined by a substantially circular arc with a radius (d1-dn) centered at the second focus (Fy).

7. The system according to any one of claims 1 to 3 and 6, wherein: The thickness (L90) of each of the one or more bremsstrahlung converters (4.1-4.n) measured along the radius of curvature does not exceed 3 mm.

8. The system according to any one of claims 1 to 3 and 6, wherein: The nth bremsstrahlung converter (4.n) closest to the target holder (5h) has a greater thickness (L90) than the first bremsstrahlung converter (4.1) closest to the focusing unit (3).

9. The system according to any one of claims 1 to 3 and 6, wherein: The conversion unit (4) comprises 1 to n bremsstrahlung converters (4.1-4.n) separated from each other by cooling channels, wherein n is between 2 and 8.

10. The system according to any one of claims 1 to 3 and 6, wherein The converter cooling system (4c) includes gas or liquid forced cooling.

11. The system according to any one of claims 1 to 3 and 6, wherein: The one or more bremsstrahlung converters (4.1-4.n) are made of tantalum (Ta) or tungsten (W) or titanium (Ti).

12. The system according to claim 1, wherein: The intersection angle ( ) is between 75° and 105° at all points.

13. The system according to claim 2, wherein: The one or more bremsstrahlung converters (4.1-4.n) have a spherical cap shape defined by a first curved cross section in the first irradiation plane (X, Z) and a second curved cross section in the second irradiation plane (Y, Z).

14. The system according to claim 4, wherein: The focusing half angle is between 30° and 45°.

15. The system according to claim 6, wherein: The second focusing point (Fy) is the same as the first focusing point (Fx).

16. The system according to claim 7, wherein: The thickness (L90) is between 0.2 mm and 2.5 mm.

17. The system according to claim 16, wherein: The thickness (L90) is between 0.5 mm and 1.5 mm.

18. The system according to claim 9, wherein: n is between 3 and 5.

19. A method for producing radioisotopes by irradiating a target with X-rays, the method comprising: • providing a system according to any one of claims 1 to 18, • loading the target (5) onto the target holder (5h), • scanning and focusing the accelerated electron beam onto the conversion unit (4) to generate X-rays, • irradiating the target with the X-rays thus generated.

20. The method according to claim 19, wherein The target (5) is selected from one of the following: 225 Ac's 226 Ra, or used to form 99m Tc 100 Mo, or used to generate 187 Re 186 W, or used to form 131 I 134 Xe, or for generating 67 Cu's 68 Zn.

Images