WO2017157879A1 - Electromagnetic drivable inserts - Google Patents

Abstract

The present invention relates to magnetically activatable inserts. In order to provide improved ways of controlling, a radiation providing seed (10) for use in radiotherapy is provided. The seed comprises a seed core (12) that is configured to generate radiation, a casing (14) providing a cavity (16), and a movable (18) insert which is guided inside the cavity. The seed core is attached to the movable insert, which is configured as a magnetic insert, such that upon applying a magnetic field with a moving component, the insert is movable relative to the casing. The insert is movable between a first position (P1) and a second position (P2). In the first position, the seed core is in a shielded arrangement within the casing, and in the second position, the seed core is in an exposed arrangement, such that in the second position, the seed provides more radiation than in the first position. The movable insert is configured to cause a movement between the first and the second position upon being moved relative to the casing. Further, the insert is a screw insert (20) that is movably hold by a threaded connection arranged along a thread axis. The screw insert is rotatable relative to the casing to cause a screw motion resulting in a movement along the thread axis. And the screw insert has a magnetization component (24) arranged transverse to the thread axis, such that upon applying a magnetic field with a rotational component, the screw insert is rotatable relative to the casing.

Description

ELECTROMAGNETIC DRIVABLE INSERTS

FIELD OF THE INVENTION

The present invention relates to a radiation providing seed for use in radiotherapy and a method for activating a device inserted into a body structure. BACKGROUND OF THE INVENTION

In medical interventional methods, medical devices are sometimes inserted in a body structure. In order to deliver power, e.g. for interventional tasks and activating and deactivating functions of the device, cables or wires are used, for example as catheter tubes or similar. However, it has been shown that sometimes wires or cables are found to be not so convenient and may, for example, bother surgical steps. Further, the use of a magnetic field for power delivery is known. For example, in radiotherapy, seeds are provided as implanted radiotherapy seeds. In WO 2014/076666 seeds are described that are switchable by the application of a magnetic field. However, it has been shown that the exact activation of the seeds may be difficult to be achieved and controlled.

SUMMARY OF THE INVENTION

There may thus be a need to provide magnetically activatable inserts with improved ways of controlling.

The object of the present invention is solved by the subject-matter of the independent claims, wherein further embodiments are incorporated in the dependent claims. It should be noted that the following described aspects of the invention apply also for the radiation providing seed for use in radiotherapy and the method for activating a device inserted into a body structure.

According to the present invention, a radiation providing seed for use in radiotherapy is provided. The seed comprises a seed core that is configured to generate radiation, a casing providing a cavity, and a movable insert, which is guided inside the cavity. The seed core is attached to the movable insert. The movable insert is configured as a magnetic insert, such that upon applying a magnetic field with a moving component, the insert is movable relative to the casing. The insert is movable between a first position and a second position. In the first position, the seed core is in a shielded arrangement within the casing, and in the second position, the seed core is in an exposed arrangement, such that in the second position, the seed provides more radiation than in the first position. The movable insert is configured to cause a movement between the first and the second position upon being moved relative to the casing. Further, the insert is a screw insert that is movably hold by a threaded connection arranged along a thread axis. The screw insert is rotatable relative to the casing to cause a screw motion resulting in a movement along the thread axis. And the screw insert has a magnetization component arranged transverse to the thread axis, such that upon applying a magnetic field with a rotational component, the screw insert is rotatable relative to the casing.

This provides the effect that the seed can be activated by a magnetic field, and can also be deactivated by also applying the magnetic field respectively.

The term "movable relative to the casing" relates to a relative movement between the insert and the casing. In one example, the insert moves and the casing remains; in another example, the casing moves and the insert remains; in a further example, the insert and the casing move. Hence, a mutual relative movement is provided, i.e. the insert is movable in relation to the casing.

The "moving component" of the magnetic field relates to a magnetic field with a field character or magnetic field distribution that is spatially changing over time in the sense that the magnetic field properties are spatially moved, for example in a two- or three- dimensional manner.

In an example, the cavity is formed by the casing. In another example, the cavity is formed by an inner container of vessel arranged inside the casing.

In an example, a magnetic field is provided with a field free point or field free line where two opposing magnetic fields cancel. Further, it is provided that the position of the field free point is moving, hence resulting in the moving component. The term "component" relates to a parameter or property of the field and not to a component such as a piece of equipment. The movement of the field free point / line may be achieved by a spatial adaption of the magnetic field. In another example, a primary magnetic field and a secondary magnetic field are provided and the spatial arrangement of the secondary field is moved.

In an example, the moving component is a mostly homogeneous component with a flux density magnitude of less than 50 mT, preferably less than 10 mT. It can have a relatively complex temporal shape, e.g. in three (sub-) components.

In an example, the moving component is a rotating component, i.e. the location of the field free point / line is moving in a rotational manner.

For example, the moving component comprises of several part-components. In on example, the rotating movement comprises several part-rotation components, e.g. quarter rotational movements in contrariwise manner.

In another example, the moving component is a translating component, i.e. the location of the field free point / line is moving in a translational manner.

In another example, the moving component is a combination of a translating and a rotating component, i.e. the location of the field free point / line is moving in a combined movement manner.

For example, an AC field or translationally moving gradient field is applied in helical mechanical guides.

In an example, a magnetic source is configured to create a magnetic field adapted to apply a mechanical attraction or repulsion force to the magnetic seed along a longitudinal axis or along a helical path, e.g. the longitudinal axis.

In an example, the "moving magnetic field", i.e. the moving component of the magnetic field, allows that the mechanical switch of the radiation is controlled directly by an applied magnetic force or torque. As a consequence, it does not require intermediary mechanism, i.e. like an elastic element (spring) or a heating element to free the radiation. This results in increased reliability and avoids the need of high frequency for heating and aspects related to applying heat. Further, compactness is optimized, without further activation means like a spring and also a wireless device.

According to an example, the screw insert has an outer thread and the casing is provided with an inner thread on the inside of the housing forming the threaded connection.

In another example, the magnetic field is having a translationally moving gradient field, and the device, i.e. the seed, is provided with helical mechanical guiding means to allow a "helical movement" caused by the translational movement in interaction with the guiding means.

As an effect, it is provided that the insert provides the movement between the first and the second position due to the movement of the insert itself relative to the casing, which, due to guidance leads to a transversal displacement of the screw insert inside the cavity.

As an effect in the rotational example with the screw insert, it is provided that the screw insert provides the movement between the first and the second position due to the rotating movement of the screw itself, which, due to the thread, leads to a transversal displacement of the screw insert inside the cavity.

However, it is also provided that another type of insert is provided that is caused to move relative, e.g. in relation, to the casing such that a movement between the two positions is provided.

In an example, the position or orientation of the insert relative to the casing is provided to be moving, i.e. the insert and/or the casing are moving. Instead of the thread also other means are provided such as guidance for helical movement, such as pin/groove connection along a helical path. Such guidance can also be provided to be along a zigzag line or wavelike curved line to allow a movement of the insert to result in a translation movement component.

According to an example, the seed core comprises radioactive material that generates radioactive radiation. The casing in a first part is provided with a radiation shielding material forming a shielding part of the casing. In a second part the casing has low Z material. In the first position, the seed core is arranged within the shielding part, and in the second position, the seed core is arranged outside the shielding part.

This provides the effect that a switchable seed is provided.

According to an example, the casing is provided as a spherical case, and a spherical inlet is rotatably arranged inside the spherical case. The spherical inlet is forming the cavity, e.g. comprising the inner thread or other guiding means for the insert. The spherical inlet further comprises a first part provided with a radiation shielding material forming a shielding part-sphere, and a second part provided with a low Z material. In the first position, the seed core is arranged within the shielding part-sphere, and in the second position, the seed core is arranged outside the shielding part-sphere.

According to an example, the seed core comprises radioactive material emitting alpha radiation. The casing, at a first portion, is provided with the inner thread and, at a second portion, with a target material for the alpha radiation to generate neutrons comprising radiation, such that, in the first position, the seed core is arranged distanced to the target material, and, in the second position, the seed core is arranged closer to the target material.

According to an example, a locking mechanism for the screw insert is provided to prevent unwanted rotation.

According to the invention, also a method is provided for activating a device inserted into a body structure. The method comprises the following steps: In a first step, a plurality of devices inserted in a body is provided. Each device comprises a movable part having a permanent magnet structure. In a first sub-step of a second step, a primary magnetic field with a field free point or field free line is generated. In a second sub-step of the second step, the position of the field free point is moved. In a third step, a movement of a movable part of a determined one of the plurality of the inserted devices is caused by displacing the field free point.

According to an aspect, a magnetic field is provided that has a moving component. This is used to move an insert in a seed, or an interventional device to rotate relative to a casing and therefore a switchable seed is provided.

These and other aspects of the present invention will become apparent from and be elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention will be described in the following with reference to the following drawings:

Fig. 1 shows a schematic illustration of an example of a radiation providing seed for use in radiotherapy.

Fig. 2 shows a further example of the radiation providing seed.

Fig. 3 shows a still further example of a radiation providing seed.

Fig. 4 shows a further schematic cross-section through a radiation providing seed.

Fig. 5A and 5B show a further example of a radiation providing seed, wherein Fig. 5A shows a longitudinal cross-section and Fig. 5B shows a transverse cross-section.

Fig. 6 shows a further functional illustration of an example of a radiation providing seed.

Fig. 7 shows another example of a radiation providing seed.

Fig. 8 shows a still further example of a radiation providing seed.

Fig. 9 shows a further example of a radiation providing seed that can be activated by the screwing mechanism.

Fig. 10 and Fig. 11 show examples of a locking mechanism of a radiation providing seed.

Fig. 12 shows another example of a radiation providing seed.

Fig. 13 shows a still further example of a radiation providing seed.

Fig. 14 shows a neutron generation version of the radiation providing seed.

Fig. 15 shows a further schematic illustration of the neutron radiation providing seed.

Fig. 16 and 17 show further functional diagrams of the activated magnetic field.

Fig. 18 shows a schematic illustration of a system for targeted magnetic activation of an inserted device.

Fig. 19 shows another example of such system.

Fig. 20 shows basic steps of an example of a method for activating a device inserted into a body structure. DETAILED DESCRIPTION OF EMBODIMENTS

Fig. 1 shows a radiation providing seed 10 for use in radiotherapy. The seed 10 comprising a seed core 12 that is configured to generate radiation. Further, a casing 14 is provided that provides a cavity 16. For example, the cavity is formed by the casing. In an option, an inner container or vessel is provided to form the cavity. A movable insert 18 is guided inside the cavity. The seed core 12 is attached to the movable insert 18. The movable insert is configured as a magnetic insert such that upon applying a magnetic field with a moving component, the insertl8 is movable relative to the casing. The insert 18 is movable between a first position PI (indicated with a hashed line) and a second position P2 (also indicated with a hashed line). In the first position PI, the seed core 12 is in a shielded arrangement within the casing 14, and in the second position P2, the seed core 12 is in an exposed arrangement such that in the second position P2, the seed 10 provides more radiation than in the first position PI . The movable insert is configured to cause a movement between the first and the second position upon being moved relative to the casing. Further, the insert is a screw insert 20 that is movably hold by a threaded connection arranged along a thread axis, also referred to as screwing direction. The screw insert is rotatable relative to the casing to cause a screw motion resulting in a movement along the thread axis. And the screw insert has a magnetization component 24 arranged transverse to the thread axis, such that upon applying a magnetic field with a rotational component, the screw insert is rotatable relative to the casing.

In an example, the insert is guided inside the casing, e.g. the insert with a smooth outer surface enabling to be moved inside the casing, and some stops inside the casing to retain the insert inside the casing when not magnetically activated are provided.

Fig. 2 shows an example, where the insert 18 is shown as the screw insert 20 with an outer thread 22. In an example, the magnetization is e.g. 45° oriented to the thread axis or screwing direction, i.e. a magnetization having a magnetization component parallel and a magnetization component perpendicular to the thread axis.

The screwing direction is relating to the thread axis in which the screw is moving upon rotation.

In an example, the casing is non-magnetized. In a further example, the casing is also magnetized.

For example, the magnetic field is moving. A moving magnetic filed relates to an example where the magnetic field generating apparatus is rotated such that the resulting magnetic field is also rotating.

The screw/thread arrangement can also be provided as helical guiding mechanism. The mechanism provides that upon rotation of an inner part inside a casing, the inner part moves relative to the casing in a moving direction, e.g. a longitudinal direction. In other words, the magnetic field with the moving component results a rotation of the insert. Due to being guided by the guiding mechanism, the rotation results in a movement component along the longitudinal direction. Hence, the guiding mechanism is acting as a thread in this respect, but does not necessarily have to provide the same tight guidance and connection.

Due to the screwing mechanism, the seed is a switchable seed, i.e. a seed that can be activated or deactivated, or simply said, a seed that can be switched on and off.

In an example, the casing is comprising an inner thread forming the cavity. For example, the outer thread of the screw insert is engaging with the inner thread of the casing.

In a further example, a viscous fluid is arranged inside the cavity, and the outer thread of the screw insert is interacting with the viscous fluid such that upon rotation of the insert, the screw insert is moving relative to the casing.

According to an option, also shown in Fig. 2, the seed core 12 comprises radioactive material that generates radioactive radiation. The casing 14 is provided with a radiation shielding material in a first part 25 forming a shielded part of the casing. In a second part 26, the casing 14 is provided with a low Z material. In the first position PI, the seed core 12 is arranged within the shielding part and in the second position P2, the seed core is arranged outside the shielding part. In Fig. 2, an intermediate state is shown, where the seed core 12 has just left the shielding part of the casing and entered the second part.

For example, the casing is made out of titanium and thus provides a titanium case. The second part may be provided by a low Z polymer thread and liner. The first part 25 providing the shielding part may be made as a gold shield and thread.

In an example, the seed core is attached to the screw insert as a longitudinally (i.e. in screwing direction) extending protrusion, and the casing is provided with a receptacle at one end such that in the second position, the seed core is resting inside the receptacle.

As mentioned above, as an option, the casing is provided with a shield in a first part providing the shielding part. Preferably, the shield is also forming a part of a thread on the inside of a housing envelope, as shown in Fig. 2 and further figures. As a further option, the casing is provided with a low Z liner also forming a non-shielding part of the thread on the inside of the housing envelope. Preferably, the low Z liner is also forming a part of the thread on the inside of a housing envelope, as indicated in Fig. 2.

In an example, instead of a low Z polymer, other low Z materials like graphite or boron nitride are provided. They also provide the effect of low radiation damage.

In an example, the shield is a gold shield. In another example, other high Z materials are used for the shield.

In an example, shown in Fig. 3, a band 28 of soft magnetic material is provided along the length of the casing. For example, the band is provided in a helical shape, or as a straight line or in form of several portions or fragments.

In another example, a helical high Z material is provided alternatively or in addition to the helically shaped band of Fig. 3 to provide a directionality of the radiation if the seed remains in an intermediate state.

In an example, there are at least two different states, in which the seed core is arranged outside the shielding part. In other words, the second position comprises two sub- states. For example, two sub-states with different directions for the radiation are provided, e.g. with a helical structure.

The term "soft" magnetic material, or magnetically soft material, relates to materials that can be magnetized, but which materials have no (or little, i.e. iHc < 1 mT/μΟ) tendency to stay magnetized. For example, paramagnetic materials are provided. In another example, a material with small coercive force is provided.

The term "hard" magnetic material, or magnetically hard material, relates to materials that stay magnetized.

In an example, in absence of a magnetic field (except the magnetic field of the earth), or at fields with a value in a lower range, high coercive force is needed.

The term "permanent magnet" relates to a magnetized material creating its own permanent, i.e. persistent magnetic field. For materials that can be magnetized, and which are also attracted to a magnet, are called ferromagnetic, and include among iron, nickel, and cobalt also e.g. alloys of rare earth materials.

For example, permanent magnets are made from hard ferromagnetic materials such as alnico and ferrite, for which a special processing is provided, e.g. in a powerful magnetic field during manufacture in order to align their internal microcrystalline structure. This processing results in that they are rather "hard" to demagnetize. For the demagnetization of a saturated magnet, a magnetic field must be applied with a strength above a threshold that depends on the coercivity of the respective material. Simply said, "hard" materials have high a coercivity and "soft" materials have a low coercivity.

The term "along the length" relates to the direction, in which the screw insert moves inside the cavity.

In an example, the soft magnetic band 28 is provided with different magnetic spectral properties along its length in order to provide for determination of the switching state of the seed.

In an example, inside the cavity, a lubricating fluid 30 is provided, as indicated in Fig. 3 as an option also applicable for other examples shown in different figures.

Fig. 4 shows a further option, according to which the casing is provided as a spherical case 32, i.e. an outer casing. A spherical inlet 34, i.e. an inner casing, is arranged inside the spherical case 32 in a movable manner, e.g. the inlet can be swiveled or rotated. This provides the effect that an orientation of the radiation is possible, since the inlet can be oriented by applying respective magnetic field components, e.g. in addition to the moving components for activating the insert like the screw.

The spherical inlet 34 is forming the cavity, e.g. comprising the inner thread, indicated with reference numeral 36, forming the cavity. The spherical inlet comprises a first part 38 provided with a radiation shielding material forming a shielding part-sphere, and a second part 40 provided with a low Z material. In the first position PI, the seed core is arranged within the shielding part-sphere, and in the second position P2, the seed core is arranged outside the shielding part-sphere.

For supporting the spherical insert inside the spherical case, a bearing fluid 42 is arranged between the spherical insert and the casing.

In an example, inside the cavity, a lubricating fluid is provided as an alpha radiation shielding liquid.

Before referring to further examples, some general aspects relating to the present invention are described in the following. The radiation providing seeds described above can be used, for example, in radiotherapy as a type of cancer therapy. This is also known as brachytherapy, where a radiation source is brought in close proximity to a target tissue. The above described seeds are suitable for example for permanent implantation of radioactive seeds that can remain in the patient and the radiation dose rate can be controlled by activating, i.e. moving the radiation seed core inside the casing. The radiation can be modulated by moving the radiation source relative to an interacting material like a gold shield.

A screwing mechanism is used to activate the radiotherapy seed. For example, on the screw, the radioactive material (¹²⁵I or ¹⁰³Pd) is placed. In the off-state, the screw rests in a compartment shielded by a few 10 μιη gold or similar material. In the initiated state, the screw is turned by a magnetic field that rotates perpendicular to the thread axis. For this, the screw is at least partly composed of a permanent magnet material. When the screw reaches the unshielded compartment, the seed is in the on-state. Soft magnetic material at both ends of the thread may be provided for the following purposes. The first purpose is to hold the screw in its position, when no rotating field is applied. The second one is to localize the seed in the, for example, magnetic particle imaging system. The third purpose is to determine the position of the screw within the seed to determine the switching state. The system can replace traditional brachytherapy seeds keeping the external dimensions exactly the same. When miniaturized, alternative delivery modes, like the transarterial route, may be applied.

The intended outer dimensions are for example, 0.8 mm in diameter and 4.5 mm in length. The screw is magnetized mainly perpendicular to the long axis of the device. One way of achieving this magnetization is to use permanent magnetic material, like FeNdB attached to the screw, e.g. in a hole in the middle of the screw. Further, also a semi-hard magnetic material may be used. Still further, also soft magnetic material can be used, e.g. as a layer within the screw in the paper or drawing plane, i.e. the same geometry as in the case of semi-hard material as in Fig. 2. The radioactive material is attached on the screw. The radioactive material is usually either ¹²⁵I or ¹⁰³Pd and the apparent activity is typically in the range of 1E7 to 1E8 Becquerel. The activity may vary for special applications. The shield of the radiation in the non-activated state consists of two parts. First, the gold shield, or any other high Z high density material, and the lubricating fluid which contains intermediate to high Z elements like P, S, CI for still rather low Z or I for relatively high Z. For a so to speak "complete" shielding of the radiation, the thickness of the gold shield may be a few 10 μιη, e.g. 50 μιη. The 1/10 value layer gold for ¹²⁵I is about 35 μιη. So for 50 μιη of gold, switching ratios are in the order of 1 to 20. The fluid inside the cavity blocks radiation to the side, when not activated. The recess in the plastic part of the thread, indicated with reference numeral 44 in Fig. 2, allows for a low absorption path in the case of activation. The whole seal is enclosed in an end welded titanium tube to provide a biocompatible surface and a hermetic seal for the radiation source.

Fig. 5A shows an example where the screwing mechanism is not achieved by thread in thread, but by a thread in a viscous fluid 46.

In other words, a screw is having an outer thread and the inner side of the casing enclosing the cavity is provided without a thread, but the fluid in between provides a holding effect such that when the screw insert is rotated, a helical relative movement is achieved. The fluid hence provides a sort of guiding connection due to its viscosity.

In another example, instead of a thread, a helical groove is provided that results in a helical guidance of the insert.

In addition to Fig. 5A, an option is provided according to which the thread is on the other surface, i.e. the inner surface of the casing enclosing the cavity, and the seed has no thread. In Fig. 5 A, a gold shield 48 is provided with a cavity, inside which the high viscosity high density fluid is provided. The seed may be provided with a structural element 50 as a magnetic screw with radioactive material in a thread 52. Further, a low Z polymer or metal 54 is provided, also forming a further portion of the cavity. Still further, soft magnetic cross elements 56 are arranged.

Fig. 5B shows a transverse cross-section of the example shown in Fig. 5A. An inner circle 58 indicates the cavity and the soft magnetic cross elements 56 are also shown inside the gold shield 48.

In an option (not shown in detail), the casing comprises an inner vessel that forms the cavity. The inner vessel is at least partly filled with a melting material that has a melting point slightly above body temperature. The seed core is movable within the inner vessel upon applying the magnetic field with the moving component when the melting material is in a melting state upon applying thermal energy to the melting material.

In Fig. 6, a further example is shown that may be provided having an outer diameter of 0.8 mm and 4.5 mm in length as a titanium rod. An inner vessel 60 is placed with a diameter of about 0.5 mm. This vessel is filled with a material 62 having a melting point slightly above body temperature. In this vessel, a sphere 64, containing radioactive material (¹²⁵I) and a magnetically semi-hard rod 66 is placed in the sphere 64. On the right side, a gold shield 68 is applied with suitable thickness to block the photons from the radioactive material to a sufficient degree. Further, between the inner vessel, or inner hull, thermo insulation material 70 may be provided as an option.

In Fig. 7, a further example is described, according to which the radioactive seed is similar to that shown in Fig. 6. Except for a light decrease in the size of the gold shield in the right-hand side and a new design of the radioactive sphere. The movable sphere consists of a thin radioactive plate 72 that is backed by a radiopaque gold layer 74. The sphere is completed by a radio-transparent material 76 like a polymer. The magnetic material for heating and movement of the sphere is augmented by a small fraction of permanent magnetic material 78 to introduce a preferred orientation.

Fig. 8 shows a further example of the seed as an augmented version of the seed in Fig. 7. The seed comprises two directional radiation sources that are located in two compartments of the inner vessel. The compartments are separated by a radiation shield 80 and contain materials with slightly different melting points. For example, in the left part of the cavity, a lower melting point material 82 is provided, and on the left side, the cavity is provided with a higher melting point material 84.

In Fig. 9, a further example of a seed is shown. This seed is activated by a screwing mechanism. Inside a titanium hull 86 with radiation shield 88 on one side, a polymer material is inserted and a thread is cut into the material. Inside the thread, a radioactive screw is inserted. The radioactivity is preferably at the cylindrical surface of the screw and a shield prevents the radiation from escaping the outer gold shield by paths through the screw. In the screw body, a permanent magnetic material is inserted with a magnetization perpendicular to the through axis.

Fig. 10 shows a further example of the seed with the screwing mechanism of Fig. 9. However, the screwing mechanism is fitted with a locking mechanism. The locking is achieved in Fig. 10 by two soft magnetic strips 90, one for the off position in the right-hand side, and one for the on position on the left-hand side. As the seed is drawn in the off position, only this soft magnetic sheet is magnetized.

In Fig. 11, an example is provided where a thin magnetic rod 92 is placed at the side of the seed to generate a homogeneous bias field.

In Fig. 12, a seed mechanism suitable for further miniaturization is shown. The radioactive and magnetic screw 94 is held in place by a Bingham fluid (or other type of visco-plastic fluid) 96 that need a minimum shear force to flow. There is no inner thread provided. The screw propels through the fluid due to rotation. The screw can travel between two containers. One container is radiopaque, the other transparent. The path between the containers is narrow and may exhibit some blocking structures 98 so that only a suitable local magnetic field sequence moves the screw between the containers. Further, the radioactive screw 94 is provided with a permanent magnet 99.

According to an example, the casing comprises an inner casing that provides the cavity. Further, a visco-plastic fluid filling is arranged inside the casing, the casing forming an outer casing. The inner casing is arranged movably within the visco-plastic fluid filling.

According to an example, a tuning arrangement is provided attached to the inner casing. The tuning arrangement is magnetically activatable to adjust the spatial orientation of the inner casing in relation to the outer casing.

In Fig. 13, in addition to the example shown in Fig. 12, a directional version of the device of Fig. 12 is shown. A spherical shell 100 is provided with a visco-plastic fluid filling 102 and further, magnetic tuning forks 104 are added.

Instead of forks, also other tuning means are provided.

When operated, the tuning forks or others reduce the viscosity within the sphere and an external magnetic field can apply a torque on the tuning forks to point the radiation into the desired direction. The tuning forks are operated by a high frequency magnetic field.

According to an example, shown in Figs. 14 and 15, the seed core comprises radioactive material emitting alpha radiation. At a first portion, the casing is provided with the inner thread. At a second portion, a target material 106 is provided for the alpha radiation to generate neutrons comprising radiation such that in the first position, the seed core is arranged distanced to the target material, and in the second position, the seed core is arranged closer to the target material. For example, the case is a titanium case with a titanium thread. Further, a polonium 210 alpha emitter is provided, indicating with reference numeral 108. Still further, the emitter is attached to the magnetic screw 110. A lubricating fluid 112 is provided that may also act as an alpha shield. In the left-hand side, beryllium or boron target 106 is provided.

In an example, the seed core contacts the target material in the second position.

The radiation is provided as neutrons comprising radiation.

In an example, the target is fixed relative to the seed structure, whereas the source is moveable relative to the seed structure.

In an example, inside the cavity, a lubricating fluid is provided as an alpha radiation shielding liquid. Fig. 15 shows an example, where an alpha emitter like polonium is used as the radiation source on the screw. For example, a polonium thread 114 is provided. The screw body is made of some relatively arbitrary engineering material and may contain a permanent magnet 116 to operate the screw. On one part of the casing, beryllium is plated, for example as an inner thread 118. If the alpha emitter is in contact with the beryllium, neutrons are produced.

As a further option, in Fig. 15, also some soft magnetic lock elements 120 are provided at the end faces.

According to a further example, not further shown, a locking mechanism for the screw insert is provided to prevent unwanted rotation. Preferably, the locking mechanism comprises one of the group of permanent magnets in the seeds and visco-plastic fluid.

In a further example, markers are provided to verify the switching state of the seed under imaging guidance, such as X-ray markers for X-ray imaging or MPI markers for MPI imaging.

In Fig. 16, a schematic illustration is shown for activating a particular one of a number of magnetically activatable screws. A primary magnetic field is provided with an arrangement resulting in a field free point 120 where fields cancel. A displaceable secondary magnetic field is provided to shift the position of the field free point, for example along a circulating movement path 122. Whereas such rotation results in a rotation 124 of a first seed 126, the effect on the neighboring seed 128 is only a swiveling motion 130. Hence, it is possible to achieve rotation for a targeted screw, whereas neighboring screws remain un- rotated.

Fig. 17 describes further the separation in the case of an access separation of the seeds. Other than in Fig. 16, the seeds are separated in their direction of rotation. If the field free point (FFP) rotates around the upper seed by moving from the drawn position in the paper plane, then to the left of the upper seed, out of the paper pane (in the direction of the viewer) to the right of the seed, passing the seed in the front, and back again to the paper plane, the magnet in the upper seed will rotate. However, the same torque, is applied to the lower seed. This seed will not rotate, as there is an additional torque indicated by the force arrows denoted with F. Due to this torque, the friction of the magnet in the bearing is increased to a level, that blocks the rotation.

In Fig. 18, a system 200 for targeted magnetic activation of an inserted device is provided. The system comprises a magnetic field generator 202 configured to generate a primary magnetic field with an arrangement resulting in a field free point where the fields cancel. A displaceable secondary magnetic field is provided to shift the position of the field free point and/or a mechanical movement of the magnetic field generator. The magnetic field generator is configured to displace the magnetic field to cause movement of a moving part of a determined one of a plurality of devices for insertion in a body. Preferably, other devices of the plurality of devices remain in the same state.

An X-ray C-arm system may be fitted with a magnet assembly to operate the seed.

It is noted that in addition, also an imaging system, such as an X-ray imaging system, is shown as an option. Further, a patient support 206 is indicated and a patient 208 with a seed region 210 is illustrated. The X-ray imaging may comprise an X-ray tube 212 and an X-ray detector 214.

In an example, the primary magnetic field is a static magnetic field.

In another example, the secondary magnetic field is homogenous.

In an example, the devices are seeds as described above.

The term "remain non-rotating" refers to the rotation of the rotating part.

In an example, only the determined device rotates, while all other devices are not rotating.

For example, the magnetic field generator has two opposing north poles. As a further magnetic arrangement, a single-sided arrangement is provided.

The addition of a mainly homogeneous field moves the field free point (FFP). However, a mechanical movement of the arrangement moves the FFP as well.

In an example of a labyrinth- like cavity, along which the screw-insert is moved, it is possible that more than one screw rotates, while only one finds the way from one side to the other as the angle needs to be precisely aligned.

In an example, the magnetic field generator is configured to cause a targeted movement of the determined device for insertion and all other devices for insertion remain non-rotating. Preferably, the magnetic field generator comprises permanent magnets with N/S poles configuration on a movable support arm to perform a helical movement in order to move the field free point actually without a rotating field.

For example, the rotating field is provided plus a movement transversal to the rotation axis.

In an example, the magnetic field generator is configured to cause a targeted rotation of the rotating part of the determined device for insertion and all other devices for insertion remain non-rotating. For example, as an imaging system, an MPI system is provided that has the capability to produce the primary and the secondary field.

According to a further example, the system comprises an imaging system of at least one of the group of a magnetic particle imaging (MPI) system, a magnetic resonance imaging system (MRI) and an X-ray/CT imaging system.

For example, Fig. 19 shows an X-ray imaging system 216 and a patient table 218. Further, a robotic arm structure 220 is provided carrying a magnetic assembly 220 to achieve the rotation of inserted devices or seeds, i.e. the rotation of the rotatable parts of these inserts or seeds.

According to an example, not further shown, the magnetic field generator comprises a primary magnetic source for generation of the primary magnetic field and a secondary magnetic source for generation of the displaceable secondary magnetic field.

Preferably, an X-ray imaging is provided and the primary magnetic source is provided by a magnetic system, and the secondary magnetic source is provided by a movable magnetic manipulator, for example a robotic arm.

For example, the magnetic system consists of a large permanent or electro magnet. In addition, as magnetic manipulator, some additional devices are provided to do the relatively fast movement, e.g. a coil system or a small portion of the field generator that moves.

The inserted device may be a temporarily implanted device (see below).

The term "transverse" relates to an orientation approximately perpendicular, i.e. for example, +/- 20° deviating from 90°, preferably a smaller deviation from 90°, or 90° = perpendicular.

The magnetic imaging system may be provided, for example, as a magnetic particle imaging system or as a magnetic resonance imaging system.

In an example, the movable magnetic manipulator is a robot with a magnetic structure attached to a movable arm.

Fig. 20 shows a method 300 for activating a device inserted into a body structure. The following steps are provided. In a first step 302, also referred to as step a), a plurality of devices inserted in a body is provided. Each device comprises a movable part having a permanent magnetic structure. In a second step, as a first sub-step 304, also referred to as step bl), a primary magnetic field is generated with a field free point. In a second sub- step 306, also referred to as step b2), the position of the field free point is moved. In a third step 308, also referred to as step c), the movement of a movable part of a determined one of the plurality of the inserted devices is caused by displacing the field free point.

In an example, each device comprises a movable part having a permanent magnet structure with a north-south pole configuration that is arranged along a line transverse to an axis of rotation of the device. The rotating part has a thread structure to cause a movement of the rotating part in direction of the axis of rotation upon rotation of the rotating part. In step c), the rotation of a rotating part of a determined one of the plurality of the inserted devices is caused by displacing the field free point. The movable part is having a thread structure to cause a movement of the rotating part in direction of the axis of rotation upon rotation of the rotating part.

According to an example, at least one device is provided as a radiation providing seed according to one of the above-mentioned examples.

Radiation therapy can be used as a type of cancer therapy. For example, in brachytherapy, a radiation source is brought in close proximity to the target tissue. Radiation sources may utilize radioactive material or some sort of X-ray sources. One option is the permanent implantation of radioactive seeds. These seeds may remain in the patient and the radiation dose rate simply decays according to the used isotope. However, according to an example it is provided to change the apparent dose rate by mechanical means. For example, low energy X-ray and/or gamma-ray emitters are provided. The radiation of those can be shielded by a thin layer of high Z material. Therefore, the radiation can be modulated by moving the radiation source relative to an interacting material like a gold shield. Since in brachytherapy, usually about 100 seeds are placed, in an example, the seeds can be addressed individually by magnetic fields to operate the seed.

In one option, alternating magnetic fields are used, which tune each seed to a specific frequency.

In another option, the absence of a static field is provided, which can also be used for imaging such as in "Magnetic particle imaging" (MPI). If the north poles of two identical magnets face each other, the fields in the middle cancel, but the field magnitude increases from this point towards all directions. The point, where the fields cancel is called the "Field Free Point" (FFP). Adding a small homogeneous field shifts the position of the field free point and the field strength at the original FFP becomes non-zero. In the imaging case, this effect was used to saturate soft magnetic material positioned not at the FFP and use an AC field to generated harmonics at the FFP. Magnetic material that is not located at the position of the original FFP remains in the state of saturation and therefore does not generate harmonics. The same effect can be used to manipulate the material. In this type of field (let's call it "selection field"), soft magnetic material will be pushed away from the field free point. With this, a switchable seed may be constructed.

In Fig. 9, a device, i.e. a seed is illustrated that operates purely mechanically. The device consists of a thread in e.g. a plastic material inside the protective titanium hull. In the OFF position, the radioactive screw rests in the rightmost position. To avoid that radiation leaks out, the radioactive material is at the outmost position of the screw, e.g. in the thread and the screw body shields the radiation. This shielding can be accomplished by a special gold shield or by choosing the right material for the screw body e.g. silver which also has favorable radiochemical properties for radioactive iodine. Inside the screw body, a permanent magnetic material (e.g. Fei₄Nd₂B) is inserted with its magnetization perpendicular to the screw axis. The radiation is switched on, if the screw is moved to the left. One example for operating the screw is to apply a homogeneous magnetic field that rotates being always perpendicular to the screw axis. In this case the screw rotates without any additional magnetic torques or forces. To selectively operate the screw, on top of the rotating field, the selection field is added with the field free point (FFP) placed on the screw position. As at the FFP position, the field is zero, nothing changes for the screw and it rotates as illustrated in Figs. 16 and 17. In the combined field, the FFP is no more at the position of the screw, but rotates around the screw. Concerning a screw located at a distance from the position of the FFP of the selection field, for the sake of simplicity, it is only considered the situation where the field component at the seed position due to the selection field is perpendicular to the seed axis. If the field amplitude is higher than the amplitude of the rotating field, the total field at the seed position does not cover all directions. This means it only oscillates around a direction and does no more rotate. Therefore, the screw only oscillates and does not rotate. In the example of the FFP movement, the FFP does no more rotate around the seed and therefore no rotation in the seed occurs as shown in Figs. 16 and 17. Hence, the selection of a seed in the plane perpendicular to the axis depends on if the PPF moves around the screw or not. The selection mechanism in screw direction relies on a different principle and is also depicted in Figs. 16 and 17. Referring to a pure rotational field without the selection field, a field in screw direction is added. Independent of the strength of the added field, this results in the same radial torque on the screw as before. What changes is the torque on an axis perpendicular to the screw direction. This torque induces a canting of the screw and increases the torque needed for the rotation. This effect depends on length, surface properties and lubrication of the screw.

In an example, the operation does not start in a flux density below 2 mT, to avoid activating the screwing mechanism by every-day magnetic fields. As an option, a shear thinning lubricant is provided. The shear thinning effect is known from e.g. tooth paste, non- dripping dye and foods like ketchup. These fiuids only flow, if enough shear force is applied. A different way to implement a locking mechanism is to add permanent magnets or soft magnetic material and hold the screw by the magnetic forces. This is illustrated in Figs. 10 and 11. In Fig. 10, the soft magnetic approach is illustrated. A thin and long strip of soft magnetic material is attached to the lids of the seed. The dimension of the strip in up-down direction is much longer than in the direction orthogonal to the paper plane. Therefore, magnetic anisotropy is generated. This means, the screw is locked in an orientation that is parallel to the strip as long as it is close enough to the ON or OFF position. In Fig. 11, the locking is achieved by a thin rod of permanent magnetic material. This material generates a fairly homogeneous field at all screw positions, and can therefore lock it in any desired position. This may be used to achieve a limited directionality of the seed. One option is to have an additional absorber in the left part of the seed e.g. a helical gold foil that describes one full loop. Depending on the position of the screw, the shadow of the gold foil has different directions and may be used to avoid critical tissue. A different approach for the directionality would be a permanent magnetic rod with a magnetization that varies in a helical way. This would change the orientation of the locked screw according to the position of the locking. If the screw is radiopaque and is provided with a radioactive surface only in part, the radiation direction can also be altered.

In order to provide delivery of seeds as trans-arterial delivery by a catheter procedure, the seeds are provided with a small diameter. For example, a diameter of 0.2 mm is provided. Considering the shielding point of view, this is achieved by ¹⁰³Pd sources, where the shielding thickness is only 30 μιη giving rise to 60μιη diameter penalty. For the 30 keV isotopes, a good (to 1 %) shielding gives rise to a diameter penalty of 200 μιη for gold. Here, a more efficient absorber may be desired. With platinum, the diameter penalty can be reduced to 170 μιη and with uranium to 130 μιη. So depleted uranium should be considered as a shielding material given the small total amount of it within all seeds in the patient. The total uranium mass for about 200 seeds would be in the order of 10 mg. The radiation would be rather negligible with a total activity of 200 seeds of less than 0.2 Bq. Furthermore, the alpha particles are shielded by the uranium itself and the necessary protective layer. Some of the rare gammas and the betas of the daughter nuclei (^234Th and ^234mPa) will reach the tissue resulting in a lifetime radiation dose well below 10 μGray. For very small seeds, the size of the radioactive material becomes significant, too. Current high activity Palladium seeds have an activity of 74 MBq (2 mCi) while the Iodide seeds have usually less than 37 MBq (1 mCi). With theoretical specific activity of 2800 TBq/g (75 kCi/g) for ¹⁰³Pd and 640 TBq/g (17 kCi/g), a cube of desired activity has a side length of 13 μηι assuming metallic palladium and 27 μιη assuming silver iodide. Therefore, seeds with diameters of roughly 100 μιη with Palladium are provided. The iodine seeds would require a little larger volume, but 200μιη diameter are provided in an example.

In Fig. 12, a seed is proposed, that can have a size almost as mall as the theoretical limit derived above. The seed is having two containers between which the radioactive material can travel. Only one container is transparent for the radiation. To avoid accidental travel of the radioactive material, the passage is narrow and has kinks and protrusions to allow only changing the containers, if the applied magnetic field is suitable just for this seed in this position and angle. To avoid mechanical vibrations, which are present in the patient due to his movement, to eventually move the screw between the containers, a fluid filling the device is provided having a special property. The fluid behaves like a solid for low shear stress and becomes liquid above a certain threshold. Such fluids are called visco-plastic fluids or "Bingham fluids" with the most common example being toothpaste. The fluid should also contain medium or high Z elements to attenuate radiation going through the connecting path and thereby reaching tissue. The whole seed may need to be covered by some protective layer e.g. a thin gold film that may be deposited also on the titanium part.

To determine approximate shear stress, a simple model with employing an infinitely long cylinder with radius r and average magnetization M may be used. In an external flux density B, the shear stress for the rotational movement \sigma_r is:

\sigma_r = \frac{r^A2 \pi 1 M B} { r 2 r \pi 1} = \frac{l } {2} M B wherein 1 being the "length" of the cylinder assumed to be large compared to the radius, so the ends of the cylinder can be neglected. As seen from the formula, the radius of the device cancels in the formula. Therefore, the rotational shear stress remains constant when scaling the device. Assuming M = 0.13 TAmu_0 A/m i.e. 10% permanent magnet content and an actuation flux density field of 1 mT, the shear stress is about 50 Pa.

In comparison, the average shear stress due to translation \sigma_t may be estimated as:

\sigma_t = \frac{r^A2 \pi 1 M G} {2 r \pi 1} = \frac{l } {2} M G r wherein G is the gradient of the flux density. In this case, the radius does not cancel so smaller devices exhibit less stress. Assuming a gradient of 1 T/m and a radius of 20 μιη, the shear stress is 1 Pa. This is much lower than in the rotational case. Therefore, it is impossible to (accidentally) operate the device using gradients. To determine, if the device is safe in case of vibrations the shear stress due to acceleration may be estimated by:

\sigma_a = \frac{r^A2 \pi 1 a YDelta \rho} {2 r \pi 1} = \frac{l} {2} r a YDelta \rho where a is the acceleration and YDelta \rho the difference in density. Assuming $a$ to be 9.81 m/s^A2 and YDelta Yrho to be about 5000 kg/m^A3, the shear stress is about 0.5 Pa.

As a proper visco-plastic fluid is a very efficient mechanism to avoid accidental actuation of the seed, the only purpose of the kinks and protrusions is to avoid the actuation of the wrong seed while using the gradient and rotating field to actuate one other. Therefore, the kinks may be rather small, much smaller than in the drawing, resulting in a diameter closer to the theoretical limit.

The miniaturized seed has no ability to direct the radiation, yet. The approach using a melting effect is no more technically feasible for this size, as thermal insulation is becoming very difficult and a sufficient temperature rise is no more expected. But the visco- plastic effect may also be used to address a seed as shown in Fig. 13. The miniature radioactive seed is now encapsulated in a sphere filled with a visco-plastic fluid. The yield stress of the fluid needs to be high enough that in expected magnetic fields, especially those applied to operate the other seeds, no rotation is observed. Rotation is only possible, if the seed oscillates thereby generating a very high shear stress. The oscillation may be generated by some tuning-fork device which is attached to the seeds. The tuning fork is made from a ferromagnetic material and resonant to the HF frequency applied or some harmonics of it. By magnetizing the tines in the same direction, they repel each other and by repeating the process using the HF magnetic field, the oscillating force is generated. The tuning forks can be used to apply the magnetic torque on the seed. Basically, the seed will orient in the direction of the applied magnetic field with some deviation due to unbalanced gravitational forces. As the direction should not be changed unintentionally, the total amount of magnetic material and the anisotropy should not be too high. The tuning fork approach is only one possibility. The system may also work with other devices that produce a torque in an alternating magnetic field. E.g. a magnet sphere in a Newtonian high viscosity fluid could be attached to the seed. If magnetic fields vary slowly, no torque is transmitted to the seed. In a fast rotating magnetic field, the torque is transmitted through the viscous coupling and the seed is turned. It is even possible to use focused ultrasound to selectively thin the visco- plastic fluid in the sphere and only a small permanent magnet is attached to the inter structure to turn the seed in the desired direction. In order to be able to provided neutron radiation that has a different biological effect than photon radiation, small neutron sources are provided.

As an alpha emitter to generate an exceedingly low amount of gammas to count as neutron source, ²¹⁰Po is provided as an isotope with only 12 ppm of 803 keV photons being emitted for each alpha particle emitted. As neutrons have at least 10 times the biological effect than photons and the average energy of the neutrons is 4.5 MeV, the radiation effect due to photons is less than 2 % of the radiation damage due to neutrons. Moreover, the photons' energy is distributed over a much larger volume and a significant fraction of the photons may leave the patient altogether. Unfortunately, with a half-life of 138 days ²¹⁰Po does not seem to be useful for permanent implants as either a very low dose rate has to be chooses or an unsafe high dose has to be delivered.

With the magnetically switchable seeds, even a high dose rate does not have to be maintained until the radiation decayed.

The implementation of such a seed is very similar to the seeds shown so far except there is no way to direct the radiation in any way. The radiation source has to be replaced with polonium and the gold shield has to be replaced with beryllium. As the mean free path of alpha particles in a liquid is only about 10 μιη, the fluid filled variants are less suitable for the purpose, but as a thick shielding is not required, the seed can still be quite small.

In Fig. 15, a proposed neutron seed is sketched. It is very similar to the seed proposed in Fig. 11. The radioactivity is deposited on the screw thread as a thin layer of polonium or a polonium compound. It needs to be thinner than the free path of the alpha particles. Therefore, in one example, the thickness is in the order of 1 μιη or less. Some of the thread in the hull is covered by beryllium. The thickness of the beryllium layer does not need to be large as the alpha particles are stopped within the first 30 μιη. Accounting for the threshold energy of the reaction, 20 μιη beryllium is provided. Other than in the case of the photon emitters, here it is possible to inverse the position if beryllium and polonium which may me a little simpler to manufacture. The seed may be provided with a stopping mechanism as shown above.

In an example, the radiation effect (dose rate) of a photon seed R_p is compared with the radiation effect of the neutron seed R_n for the same activity a. The radiation effect of the photon seed is:

R_p = a * \eta_ {escape-photon} * E_ {photon} * W_ {photon} where \eta_ {escape} is the efficiency of photon escape from the seed assumed to be 0.5 and W_ {photon} is the relative biological effectiveness (RBE) of photons which is 1. E_ {photon} is the average photon energy which is 28 keV for ¹²⁵I. In the neutron case the dose rate is:

R_n = a * \eta_ {escape-neutron} * \eta_{production_neutron} * E_ {neutron} * W_ {neutron}

where \eta_{production_neutron} is the production efficiency of neutrons and W_ {neutron} the RBE of 4.5 MeV neutrons which is about 10. E_ {neutron} is the average neutron energy of the Po-Be source and about 4.5 MeV. \eta_ {escape-neutron} is the escape probability of neutrons out of the seed and very close to 1. The theoretical efficiency of neutron production being 77ppm but we cannot expect to have this value in the switchable seed geometry, as only half of the neutrons travel into the right direction. Therefore, an efficiency of 38 ppm is assumed. In total, the dose rate ratio for the same activity is:

\frac{R_n} {R_p} = \frac{\eta_ {escape-neutron} * \eta_{production_neutron} * E_ {neutron} * W_ {neutron} } {\eta_ {escape-photon} * E_ {photon} * W_ {photon} } \approx 0.12

So for the same activity about 12% the dose rate with neutrons is provided. This means, instead of 37 MBq (1 mCi) for an ¹²⁵I seed, 300 MBq (8 mCi) for an Po-Bi seed are provided. Assuming the theoretical specific activity of 1.66el4 Bq/g (4490 Ci/g) and a density of 9196 kg/m³, the needed polonium volume is 2e-13 m³ or a cube with 58 μιη side length. Assuming a screw with a diameter of 0.4 mm (total seed diameter 0.5 mm) and a screw length of 0.4 mm (total seed length of 1 mm), it is provided a layer thickness of 0.5 μιη even without taking the enlarged surface due to the thread into account. Shrinking the device could be accomplished by further enlarging the surface area e.g. by a higher aspect ratio thread or by using the frontal face of the screw, too.

Operating the screw may need a precise alignment of fields, while the patient may move; or other events disturb the operation of the screw. Therefore, a feedback mechanism is provided to check if the operation of the seed works. One option is to check with a Geiger counter the chance of activity while operating a screw. However, this gives only confidence that some operation happened, but does not tell which seed. Using a collimated radiation detector like an Anger camera improves the situation somewhat, but does not indicate where the seeds in off state are. Still such a device might be useful to locate seeds in on state that migrated far away from the implantation site. In an example, for operating the seeds, the position and orientation is provided with high accuracy. For example, imaging modalities are provided to guide the magnetic field. The modalities are Ultrasound, MRI, CT, X-ray and MPI.

Ultrasound is a very versatile imaging technique. In an example, special markers, like resonators are provided to detect the state of the seed.

MRI is an excellent imaging method especially in terms of soft tissue contrast. The seeds could be identified by their susceptibility artifact and, if the artifact is small enough, it could be precisely determined which seed should be operated as the surrounding tissue may be identified. In an example, the magnetic field is ramped down, to provide field cycling MRI.

CT is also a method to image the seeds and identify the tissue they are in, and CT can resolve the internal structure of (at least) the larger seeds thereby identifying their switching state.

Simple projection X-ray may also solve the problems of CT. As the shape and size of the seeds is known, only two projections are needed to determine spatial position. The high resolution detector allows determining the internal structure of the seeds including the smaller designs. By collimating the X-ray field of view to not much more than the seed size, it is feasible to image a seed repeatedly without prohibitive high dose. Additionally, C-arm systems provide enough space to apply a magnetic field generator simultaneously. At least for the very small (trans-arterial) seeds, a very high resolution system is desired with a small focal spot diameter a small (<100 μιη) detector pixels. A very small but high resolution detector may be added to a conventional detector, as only a small field of view is needed. The small beam width may allow using the detector without anti-scatter grid (or maybe just a tube around the detector) to increase X-ray photon efficiency and resolution. In Fig. 18, a sketch of a permanent magnet system within an X-ray system is shown. Clearly there is enough space for both components still leaving a considerable angle accessible for X-ray imaging. This is needed for a determination of all seed properties. In this image, the geometric magnification of an X-ray system is used to maximize the resolution, which is critical for proper assessment of the seeds.

MPI systems inherently have the ability to operate the seeds. For example, the seeds in Figs. 10 and 11 incorporate soft magnetic material that would make detectable signal in MPI allowing determining the location of the seed. They also allow determining the switching state. If the screw is near the soft magnetic locking device, there will be an offset field. Therefore, the position would be determined incorrectly by MPI. The deviation of the localization depends on the gradient strength. The two locking soft magnetic materials may also differ in their spectral response e.g. by having different hysteresis. Hence, it is possible to determine at which end of the seed the screw rests. If the soft magnetic locks exhibit different directions of anisotropy, it is also possible to determine the direction and rotation of the seed. Therefore, all relevant parameters concerning the seed can be determined. The surrounding tissue may be imaged by MPI or by using the scanner in MRI mode if available.

The field generator is provided for at least three things. First it has to provide a sufficient gradient strength to address the seeds individually. Second, it has to change fast enough to switch the seeds in a reasonable time and third, only for the thermal seeds, it has to provide a HF field with sufficient high amplitude and frequency.

To estimate the needed gradient strength, it is determined at what distance the seeds shall be switched individually and at which flux density they should start moving. Seeds should be rarely closer than 5 mm to each other and if they are closer, they may be switched simultaneously. So the desires minimum separation is about 5 mm. The minimum field to operate is determined by the field at which the seeds shall definitely not operate, i.e. the minimum field for rotation. Around magnetic equipment, like MRI scanners, the line of 0.5 mT flux density is marked as potential hazardous area for people with implants. Setting the threshold 4 times as high, the minimum flux density is estimated to be 2 mT. The ratio of the two values leads to a minimum gradient of 0.4 T/m. For a field free point, the gradient in one direction is double the value of the other direction. This leads to a minimum gradient in the strong direction of 0.8 T/m. It is also possible to operate the seed in a higher field strength as long as the precision of the minimum operating field is 2 mT. E.g. the seeds operate at a minimum of 4 mT with a spread of 3 to 5 mT. Such a field can be generated using permanent magnets. For example, an assembly of two opposing cylindrical permanent magnets with a diameter of 20 cm and a length of 25 cm each separated by 40 cm generates 1 T/m in the center assuming a magnetization of the permanent magnets of 1.3 Τ/μ₀. The mass of the assembly would be about 125 kg. An electromagnet with the same performance has typically roughly the same size and maybe a little heavier. The width of a patient is typically less than 30 cm. Therefore, the FFP can be moved by 10 cm with this assembly. To switch seeds outside this field of operation, in the case of permanent magnets, at least one pole shoe has to be changed. Full patient coverage may be reached with 2 to 3 permanent magnet assemblies.

The speed of rotation of the screws determines the speed of the whole procedure. Switching all seeds should be performed within half an hour. There are roughly 80 seeds. Assuming a thread diameter of 0.5 mm, 4 mm length and 0.2 diameters movement per turn, 40 turns for each seed is needed. In total 3200 turns are needed. So, about 2 turns per second is the minimum goal. Such a speed can be realized by pure mechanical means as the radius of the movement of the magnet assembly is only about 5 mm. The flux density chance is 4*2mT/0.5s = 16 mT/s, i.e. orders of magnitude below the threshold for nerve stimulation of about 20 T/s.

The last point, the coils for generating the HF have been described in the context of MPI. Basically resonant coils made from high frequency litz wire can generate the desired 4 mT and such a flux density in axial direction is below the nerve stimulation threshold at 150 kHz. Operation at even higher frequencies would be feasible, too.

It has to be noted that embodiments of the invention are described with reference to different subject matters. In particular, some embodiments are described with reference to method type claims whereas other embodiments are described with reference to the device type claims. However, a person skilled in the art will gather from the above and the following description that, unless otherwise notified, in addition to any combination of features belonging to one type of subject matter also any combination between features relating to different subject matters is considered to be disclosed with this application.

However, all features can be combined providing synergetic effects that are more than the simple summation of the features.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing a claimed invention, from a study of the drawings, the disclosure, and the dependent claims.

In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfil the functions of several items re-cited in the claims. The mere fact that certain measures are re-cited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. A radiation providing seed (10) for use in radiotherapy, the seed comprising:

a seed core (12) that is configured to generate radiation;

a casing (14) providing a cavity (16); and

a movable (18) insert which is guided inside the cavity;

wherein the seed core is attached to the movable insert;

wherein the movable insert is configured as a magnetic insert, such that upon applying a magnetic field with a moving component, the insert is movable relative to the casing;

wherein the insert is movable between a first position (PI) and a second position (P2) such that the relative position or orientation of the insert with respect to the casing is changed from a first position or orientation to a second position or orientation;

wherein in the first position, the seed core is in a shielded arrangement within the casing, and wherein in the second position, the seed core is in an exposed arrangement, such that in the second position, the seed provides more radiation than in the first position;

wherein the movable insert is configured to cause a movement between the first and the second position upon being moved relative to the casing; and

wherein the insert is a screw insert (20) that is movably hold by a threaded connection arranged along a thread axis; wherein the screw insert is rotatable relative to the casing to cause a screw motion resulting in a movement along the thread axis; wherein the screw insert has a magnetization component (24) arranged transverse to the thread axis, such that upon applying a magnetic field with a rotational component, the screw insert is rotatable relative to the casing.

2. Seed according to claim 1, wherein the screw insert (20) has an outer thread

(22) and the casing is provided with an inner thread on the inside of the housing forming the threaded connection.

3. Seed according to claim 1 or 2, wherein the seed core comprises radioactive material that generates radioactive radiation; wherein the casing in a first part (25) is provided with a radiation shielding material forming a shielding part of the casing, and in a second part (26) with a low Z material;

wherein, in the first position, the seed core is arranged within the shielding part, and in the second position, the seed core is arranged outside the shielding part.

4. Seed according to claim 3, wherein the casing is provided with a shield in a first part providing the shielding part;

wherein, preferably, the shield is also forming a part of a thread on the inside of a housing envelope; and

wherein, further preferably, the casing is provided with a low Z liner also forming a non-shielding part of the tread on the inside of the housing envelope;

wherein, preferably, the low Z liner is also forming a part of the thread on the inside of a housing envelope.

5. Seed according to claim 3 or 4, wherein the casing is provided as a spherical case (32); and wherein a spherical inlet (34) is rotatably arranged inside the spherical case; wherein the casing comprises an outer casing (32) and an inner casing movably mounted inside the outer casing;

wherein the spherical inlet is forming the cavity;

wherein the spherical inlet comprises a first part provided with a radiation shielding material forming a shielding part-sphere, and a second part provided with a low Z material; and

wherein, in the first position, the seed core is arranged within the shielding part-sphere, and in the second position, the seed core is arranged outside the shielding part- sphere.

6. Seed according to one of the preceding claims, wherein the casing comprises an inner vessel that forms the cavity;

wherein the inner vessel is at least partly filled with a melting material that has a melting point slightly above body temperature; and

wherein the seed core is movable within the inner vessel upon applying the magnetic field with the moving component when the melting material is in a melting state upon applying thermal energy to the melting material.

7. Seed according to one of the preceding claims, wherein the casing comprises an inner casing that provides the cavity; and

wherein a visco-plastic fluid filling is arranged inside the casing, the casing forming an outer casing; and wherein the inner casing is arranged movably within the visco- plastic fluid filling.

8. Seed according to one of the preceding claims, wherein a tuning arrangement is provided attached to the inner casing, and wherein the tuning arrangement is magnetically activatable to adjust the spatial orientation of the inner casing in relation to the outer casing.

9. Seed according to one of the preceding claims, wherein the seed core comprises radioactive material emitting alpha radiation; and

wherein the casing, at a first portion, is provided with an inner thread; and, at a second portion, with a target material (106) for the alpha radiation to generate neutrons comprising radiation, such that, in the first position, the seed core is arranged distanced to the target material; and, in the second position, the seed core is arranged closer to the target material.

10. Seed according to one of the preceding claims, wherein a locking mechanism for the screw insert is provided to prevent unwanted rotation.

11. Seed according to one of the preceding claims, wherein the locking mechanism comprises one of the group of permanent magnets in the seeds, mechanical guiding elements, mechanical stops and visco-plastic fluid.

12. A method (300) for activating a device inserted into a body structure, the method comprising the following steps:

a) providing (302) a plurality of devices inserted in a body;

wherein each device comprises a movable part having a permanent magnet structure;

bl) generating (304) a primary magnetic field with a field free point;

b2) moving (306) the position of the field free point; and c) thereby causing (308) movement of a movable part of a determined one of the plurality of the inserted devices by displacing the field free point.