WO2014076666A1

WO2014076666A1 - Energy application system for applying energy to an object

Info

Publication number: WO2014076666A1
Application number: PCT/IB2013/060172
Authority: WO
Inventors: Bernhard Gleich
Original assignee: Koninklijke Philips N.V.; Philips Deutschland Gmbh
Priority date: 2012-11-19
Filing date: 2013-11-15
Publication date: 2014-05-22

Abstract

The invention relates to an energy application system for applying energy to an object, particularly to a low dose rate brachytherapy system. The system includes an energy application device (6), which is preferentially a seed to be introduced into the object and which comprises a radioactive unit (10) for applying the energy and a switching unit (8, 1, 12) for modifying the energy applied to the object, wherein the switching unit is adapted 5 to be switchable by a field like a magnetic or ultrasound field generated outside of the object. By using this energy application device it can be switched, in particular, activated, from the outside of the object, only if it has reached a desired location within the object, to which energy should really be applied. This allows for an improved accuracy of applying energy to the object.

Description

Energy application system for applying energy to an object

FIELD OF THE INVENTION

The invention relates to an energy application system, an energy application method and an energy application computer program for applying energy to an object. The invention particularly relates to a low dose brachytherapy system, a low dose brachytherapy method and a low dose brachytherapy computer program.

BACKGROUND OF THE INVENTION

WO 2008/111065 Al discloses a low dose rate brachytherapy seed comprising thulium- 170 placed within a casing. A layer of a radiation emission modifying metal is provided either internally within the casing or on the outer surface thereof.

During a low dose rate brachytherapy it is often difficult to place the seeds correctly, for instance, such that a tumor receives almost all radiation and the surrounding tissue is not affected or only affected a little. This difficulty in placing the low dose rate brachytherapy seed can lead to a non-optimal placing, which in turn may lead to an inaccurate irradiation of a desired region like a tumor region.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an energy application system, an energy application method and an energy application computer program for applying energy to an object, which allow for an improved accuracy in applying the energy. It is a further object of the present invention to provide an energy application device, a field generating device and a monitoring device for being used in the energy application system.

In a first aspect of the present invention an energy application system for applying energy to an object is presented, wherein the energy application system comprises: - an energy application device to be introduced into the object, the energy application device comprising a radioactive unit for emitting radioactive radiation for applying the energy and a switching unit for modifying the energy applied to the object, wherein the switching unit is adapted to be switchable by a field generated outside of the object and traversing the object for reaching the energy application device, a field generating device for generating the field.

Since the energy application device comprises a radioactive unit for emitting radioactive radiation for applying the energy to the object and a switching unit for modifying the energy applied to the object, wherein the switching unit is adapted to be switchable by a field generated outside of the object and traversing the object for reaching the energy application device, and since the field generating device can generate this field for switching the switching unit of the energy application device, the degree of energy applied to the object can be amended, after the energy application device has been introduced into the object. In particular, the degree of energy applied by the energy application device can be modified depending on the actual position of the energy application device within the object. Thus, if the energy application device is arranged at a desired location within the object, at which energy should be applied, the energy application device can be operated to apply a relatively high amount of energy, wherein, if the energy application device is arranged at a location within the object, at which the energy should not be applied, the energy application device is preferentially not operated to apply the high amount of energy. This allows improving the accuracy of applying energy to the object.

The energy application system is preferentially a low dose rate brachytherapy system comprising an energy application device being a low dose rate brachytherapy seed, wherein the degree of radiation applied by the low dose rate brachytherapy seed can be modified, after the low dose rate brachytherapy seed has been implanted into the object, which is preferentially a living being like a person or an animal.

Since the field is generated outside of the object and traverses the object for reaching the energy application device, it is, for example, not necessary to reach into the object for modifying the energy applied within the object.

The switching unit is preferentially adapted to be switchable by a magnetic field and/or an ultrasound field. These fields allow switching the switching unit from outside of the object in a reliable way. However, also other kinds of fields may be used for switching the switching unit from outside the object like an electric field, an electromagnetic field, et cetera.

The switching unit is preferentially adapted to switch the energy application device from a first state to a second state, wherein in the second state more energy is applied to the object than in the first state, wherein the field generating device is adapted to generate the field such that the energy application device is switchable from the first state to the second state in a spatially confined region only. Preferentially, in the first mode a first energy and in the second mode a second energy is applied, wherein the ratio of the first energy to the second energy is preferentially 1/8 or smaller, further preferred 1/10 or smaller and even further preferred 1/50 or smaller. It is also possible that in the first mode the radioactive unit does not apply any energy to the object, whereas in the second mode the radioactive unit applies energy.

If the energy application system comprises several energy application devices, in particular, several low dose rate brachytherapy seeds, which are introduced and distributed within the object, wherein some of these energy application devices are arranged in a region, in which energy should be applied to the object, and wherein some other energy application devices are arranged in regions, in which the energy should not be applied, the field generating device can generate the field such that only in regions, in which energy should be applied, the energy application devices apply a high radiation dose, whereas in the other regions the energy application devices apply a much smaller energy or no energy at all to the object. This allows locally applying the energy in desired regions within the object, even if the energy application devices are also present in other regions within the object. The object can be, for instance, a person, wherein the spatially confined region can be the region of a tumor to be treated. The spatially confined region can have dimensions in the range of some centimeters or even some millimeters.

The energy application device is preferentially adapted to be heatable by the field, wherein the switching unit is adapted to be switchable depending on heat. This allows modifying the energy applied to the object by using the radioactive radiation emitted by the radioactive unit in a simple way by just heating the energy application device, in particular, the low dose rate brachytherapy seed.

The energy application device may comprise a heating material heatable by interacting with the field for generating heat for switching the switching unit. In particular, the heating material can comprise magnetic material for generating heat by interacting with a magnetic field. For instance, the energy application device can comprise a magnetic shell, which may be magnetically heatable. However, the energy application device can also comprise other materials for interacting with other fields for generating the heat. Moreover, the energy application device may also be indirectly heated, wherein the surrounding of the energy application device within the object is heated by the field. For instance, if the object is a living object and the surrounding is tissue, the surrounding tissue may be heated by an ultrasound field, i.e. ultrasound waves, in particular, by focused ultrasound waves. The field generating device can be adapted to provide an offset magnetic field and an oscillating magnetic field, wherein the offset magnetic field can be shaped such that the energy application device comprising magnetic material is heated in a spatially confined region within the object. Moreover, the energy application device can comprise a magnetic element for concentrating a magnetic flux at the energy application device. The magnetic material used for generating the heat depending on a magnetic field externally generated by the field generating device can be comprised in an outer shell of the energy application device. Alternatively or in addition to the magnetic material, the outer shell can include an x- ray shielding material for shielding x-rays, which may have been generated within the energy application device by the radioactive radiation and/or an aerogel.

In an embodiment, the switching unit comprises shielding elements for shielding the radioactive radiation emitted by the radioactive unit and a dissolve material, in which the radioactive unit is dissolvable, if heated above a dissolve temperature, wherein the shielding elements are distributed within the dissolve material and wherein the switching unit is adapted such that the energy application device is switchable between a first mode, in which the temperature of the dissolve material is below the dissolve temperature and in which the dissolve material with the distributed shielding elements encloses the radioactive unit, and a second mode, in which the temperature of the dissolve material is above the dissolve temperature and the radioactive unit is dissolved in the dissolve material. The shielding elements have eventually a high atomic number being preferentially larger than 70.

The shielding elements can comprise, for instance, tungsten and/or platinum and/or uranium and/or gold.

The energy application device can be adapted to be reversible switchable between a first mode, in which less energy is applied to the object, and a second mode, in which more energy is applied to the object, by generating the field and switching the switching unit accordingly. Thus, the energy application system cannot only be adapted to modify the radiation applied to the object such that the applied radiation dose is increased, in particular, activated, but the applied radiation dose may also be decreased, in particular, deactivated. For instance, the applied radiation may be switched on and switched off as desired.

In an embodiment, the switching unit comprises a first region surrounded by a first material shielding the radioactive radiation emitted by the radioactive unit more and a second region surrounded by a second material shielding the radioactive radiation emitted by the radioactive unit less, wherein the switching unit is adapted such that the radioactive unit is movable from the first region to the second region in dependence of the generated field. The switching unit may also be adapted such that the radioactive unit is movable from the second region to the first region in dependence of the generated field. Thus, the energy application unit may be reversibly switchable, in particular, reversibly activated and deactivated by using the generated field.

For moving the radioactive unit from the first region into the second region and optionally vice versa the switching unit can use a magnet for providing magnetic forces for moving the radioactive unit, a spring for using spring forces for moving the radioactive unit, et cetera. For instance, in an embodiment the energy application device is adapted to be heatable by the externally generated field, wherein the switching unit comprises a biased spring, which is attached to the radioactive unit and which is embedded in a spring holding material adapted to hold the spring in its biased state, if the temperature of the spring holding material is below a spring holding temperature, and to allow the spring to relax, if the temperature of the spring holding material is above the spring holding temperature, wherein the switching unit is adapted such that the radioactive unit is in the first region, if the temperature of the spring holding material is below the spring holding temperature, and in the second region, if the temperature of the spring holding material is above the spring holding temperature.

In a further embodiment the radioactive unit is adapted to be movable by an electrical field, wherein the switching unit is adapted to generate an electrical field for moving the radioactive unit from the first region to the second region depending on the field generated by the field generating device. The switching unit can also be adapted to generate an electrical field for moving the radioactive unit back from the second region to the first region depending on the field generated by the field generating device. The electrical field can be generated, for instance, by induction, wherein the external field can be a magnetic field and wherein the energy application device can comprise a corresponding inductor, in particular a corresponding coil.

The energy application device can apply the radioactive radiation emitted by the radioactive unit directly to the object, in order to provide the energy to the object, or the radioactive radiation emitted by the radioactive unit can at least partly be converted into another kind of energy, for instance, into bremsstrahlung, wherein this other kind of energy can be used for applying the energy to the object. For instance, the switching unit comprises a first region surrounded by a first material having a smaller atomic number and a second region surrounded by a second material having a larger atomic number, wherein the switching unit is adapted such that the radioactive unit is movable from the first region to the second region in dependence of the externally generated field. If the radioactive unit is surrounded by the first material having the smaller atomic number less bremsstrahlung is generated and if the radioactive unit is surrounded by the second material having a larger atomic number more bremsstrahlung is generated, wherein the bremsstrahlung can be applied to the object for providing the energy to the object. In this embodiment the radioactive unit comprises preferentially sulfur-35.

It is further preferred that the radioactive unit emits radiation in the range of 10 to 30 keV. The radioactive unit preferentially comprises radioactive isotopes emitting the radiation. In particular, the radioactive unit preferentially comprises at least one of the following radioactive isotopes: germanium-71, palladium- 103, caesium-131, iodine- 125 sulfur-35. The radiation within the range of 10 to 30 keV can penetrate at least several millimeters into tissue and can be stopped by, for instance, a few 10 μιη of a shielding material. This radiation is therefore particularly suited for being used by a low dose rate brachytherapy system.

The energy application system may further comprise a monitoring device for detecting the energy applied by the energy application device for monitoring the application of energy. In particular, the monitoring device can be adapted to detect the distribution of the applied energy within the object. It can comprise a single photon emission computed tomography (SPECT) system for detecting the energy and determining the distribution depending on the detected energy.

In a further aspect of the present invention an energy application device for being used in an energy application system as defined in claim 1 is presented, wherein the energy application device is adapted to be introduced into the object, wherein the energy application device comprises a radioactive unit for emitting radioactive radiation for applying the energy and a switching unit for modifying the energy applied to the object, wherein the switching unit is adapted to be switchable by a field generated outside of the object and traversing the object for reaching the energy application device.

In a further aspect of the present invention a field generating device for being used in an energy application system as defined in claim 1 is presented, wherein the field generating device is adapted to generate a field being adapted to switch a switching unit of an energy application device of the energy application system for modifying the energy applied to an object. In a further aspect of the present invention a monitoring device for monitoring an application of energy performed by an energy application system as defined in claim 1 is presented, wherein the monitoring device is adapted to detect the energy applied by the energy application device of the energy application system.

In a further aspect of the present invention an energy application method for applying energy to an object by using the energy application system as defined in claim 1 is presented, wherein the energy application method comprises modifying the energy, which is applied to the object by using a radioactive unit emitting radioactive radiation, by switching a switching unit of an energy application device of the energy application system, wherein the switching unit is switched by generating a field outside of the object, which traverses the object for reaching the energy application device.

In a further aspect of the present invention an energy application computer program for applying energy to an object by using the energy application system as defined in claim 1 is presented, wherein the energy application computer program comprises program code means for causing an energy application system as defined in claim 1 to carry out the steps of the energy application method as defined in claim 14, when the computer program is run on a computer controlling the spatial arrangement modifying device.

It shall be understood that the energy application system of claim 1, the energy application device of claim 11, the field generating device of claim 12, the monitoring device of claim 13, the energy application method of claim 14, and the energy application computer program of claim 15 have similar and/or identical preferred embodiments, in particular, as defined in the dependent claims.

It shall be understood that a preferred embodiment of the invention can also be any combination of the dependent claims with the respective independent claim.

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

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

Fig. 1 shows schematically and exemplarily an embodiment of a spatial arrangement modifying device of an energy application system,

Fig. 2 shows schematically and exemplarily an embodiment of a low dose rate brachytherapy seed of the energy application system in an inactive state, Fig. 3 shows schematically and exemplarily the low dose rate brachytherapy seed in an active state, and

Figs. 4 to 7 show schematically and exemplarily further embodiments of a low dose rate brachytherapy seed.

DETAILED DESCRIPTION OF EMBODIMENTS

Figs. 1 and 2 exemplarily illustrate an embodiment of an energy application system for applying energy to an object. In this embodiment the energy application system is a low dose rate brachytherapy system and the object is a person 1 lying on a support means like a patient table 2. A region 3 within the person 1 comprises a tumor and should be treated by applying energy to this region.

The low dose rate brachytherapy system comprises an energy application device 6 schematically and exemplarily shown in Fig. 2. In this embodiment the energy application device 6 is a low dose rate brachytherapy seed 6. The low dose rate

brachytherapy seed has preferentially a diameter being smaller than 100 μιη. It has been introduced into the region 3 within the person 1 by using, for instance, a catheter and comprises a radioactive unit 10 for emitting radioactive radiation for applying the energy and a switching unit for modifying the energy applied to the person 1 , wherein the switching unit is adapted to be switchable by a field generated outside of the person 2 and traversing the person 2 for reaching the low dose brachytherapy seed 6. The energy application system further comprises a field generating device 4 for generating the field used for switching the switching unit. In this embodiment the switching unit comprises shielding elements 11 for shielding the radioactive radiation emitted by the radioactive unit 10 and a dissolve material 12, in which the radioactive unit 10 is dissolvable, if heated above a dissolved temperature. The shielding elements 11 are distributed within the dissolve material 12, wherein the switching unit is adapted such that the low dose rate brachytherapy seed 6 is switchable between a first mode, in which the temperature of the dissolved material 12 is below the dissolved temperature and in which the dissolved material 12 with the distributed shielding elements 11 encloses the radioactive unit 10, and a second mode, in which the temperature of the dissolved material 12 is above the dissolved temperature and the radioactive unit 10 is dissolved in the dissolved material 12. Thus, in this embodiment the low dose rate brachytherapy seed 6, in particular, the switching unit, is switchable depending on heat.

For generating the heat the low dose rate brachytherapy seed comprises an outer shell 7 including a magnetic part 8, which can be regarded as being a magnetic sub- shell, and an aerogel part 9 enclosing the magnetic part 8 of the outer shell 7. Since the energy applied to the person 1 can be modified by using the dissolvable material 12, the shielding elements 11 and the magnetic part 8, which interacts with the externally generated magnetic field, these components of the low dose brachytherapy seed can be regarded as forming the switching unit in this embodiment.

The switching unit is adapted to switch the low dose rate brachytherapy seed 6 from a first mode to a second mode, wherein in the second mode more energy is applied to the person 2 than in the first mode, wherein the field generating device 4 is adapted to generate the field such that the low dose rate brachytherapy seed 6 is switchable from the first mode to the second mode in a spatially confined region only.

Preferentially, in the first mode a first energy is applied and in the second mode a second energy is applied, wherein the ratio of the first energy to the second energy is preferentially 1/8 or smaller, further preferred 1/10 or smaller and even further preferred 1/50 or smaller. It is also possible that in the first mode the radioactive unit does not apply any energy to the object, whereas in the second mode the radioactive unit applies energy.

In this embodiment the field generating device 4 is a magnetic device applying a high frequency magnetic field to the low dose rate brachytherapy seed 6 within the spatially confined region 3 for heating the same. The magnetic device can be adapted to provide an offset magnetic field and an oscillating magnetic field, wherein the offset magnetic field can be shaped such that the low dose rate brachytherapy seed is heated in the spatially confined region 3 within the person 1. In particular, the magnetic device can be similar to the magnetic device used in magnetic particle imaging as disclosed, for instance, in the article

"Tomographic imaging using the nonlinear response of magnetic particles" by B. Gleich et al, Nature, volume 435 (2005). Thus, the field generating device 4 is adapted to activate the low dose rate brachytherapy seeds only in the spatially confined region 3 within the person 1. If a low dose rate brachytherapy seed 6 is not within the region 3, the low dose rate brachytherapy seed will not be activated. In Fig. 1 the magnetic field is only schematically indicated by the arrow 5.

Referring again to Fig. 2, the shielding elements 11 can be, for instance, one of the following elements: tungsten, platinum, uranium, gold. The radioactive unit 10 and the dissolve material 12, which can also be regarded as being a matrix material, are adapted such that the dissolve material 12 melts, when heated, and that the radioactive unit 10 dissolves in the melted dissolve material 12. In the situation shown in Fig. 2, the radioactive material 10 is well contained in the matrix material 12 with the high atomic number shielding elements 11 that shield the radiation. The shielding elements 11 preferentially provide a porous shielding having a high density of about 10 kg/1.

Fig. 3 shows schematically and exemplarily the situation, after the radioactive unit 10 has been dissolved into the dissolve material 12. By dissolving the radioactive unit 10 in the dissolve material 12, at least a part of the radioactive unit 10 is moved towards the outer shell 7, thereby lessening the shielding such that the energy applied to the confined region 3 within the person 1 is increased, in particular, the application of the energy to the region 3 is activated. The switching can therefore be performed by a physical movement of radioactive isotopes within the low dose brachytherapy seed, which preferentially comprises a material shielding the radiation of the isotopes, i.e. which comprises the shielding elements. If radioactive isotopes move to the surface of the seed, the shielding effect is reduced, in particular disappears, and the surrounding tissue is irradiated.

The radioactive unit 10 is preferentially adapted to emit soft x-rays or soft gamma-rays within the range of 10 to 30 keV. This kind of radiation can penetrate several millimeters into the tissue for treating the region 3 within the person 1 and can be stopped by the shielding elements 11 along a length of a few 10 μιη. For providing the radiation the radioactive unit 10 preferentially comprises radioactive isotopes, wherein the radioactive isotopes of the radioactive unit 10 preferentially include at least one of germanium-71, palladium- 103, caesium-131 and iodine-125. In the following table these radioactive isotopes are listed together with the respective energy of the radiation and the respective penetration depths defined as the attenuation to 1/e.

The radioactive unit 10 preferentially emits soft x-rays and/or soft γ-rays. However, depending on the used radioactive isotope also a β-particle emission may occur, especially if palladium- 103 is used as radioactive isotope. The β-particles are also shielded by the shielding elements, in particular, by the high atomic number material, but the β-particles may produce high energy x-rays in the shielding elements. If these high energy x-rays are not shielded in an efficient way, the switching ratio, i.e. the ratio of the intensities of the radiation applied to the region 3 within the person 1 before heating the low dose rate brachytherapy seed 6 and after the dissolve material has been melted, may be relatively small. For instance, in the case of palladium- 103 the switching ratio may be about 10 percent due to this additional x-ray effect. Therefore, in an embodiment the shielding element further comprises a β-particle absorber with high density but low atomic number. This further shielding material can have an atomic number being smaller than 30 and can be, for instance, magnesium fluoride or iron. The density of this additional β-particle absorber may be larger than 1.5 kg/1 and more preferred larger than 2.5 kg/1. For instance, this additional shielding material can be diamond.

In the activated state, i.e. when the dissolve material has been melted, the x- rays may be generated and may contribute to the irradiation of the region 3, in particular, the irradiation of the tumor region. The outer shell can comprise a further part, i.e. a further sub- shell, forming an additional low atomic number high density outer shield, if the β-particles generate a too high local dose around the low dose rate brachytherapy seed. Also this low atomic number high density outer shield may comprise an atomic number being smaller than 30, for instance, the outer shield may comprise iron or magnesium fluoride. Moreover, the density of the low atomic number material may have a density being larger than 1.5 kg/1 and more preferred larger than 2.5 kg/1. For instance, this additional shielding material can be diamond.

The energy application system can comprise a single low dose rate brachytherapy seed or several low dose rate brachytherapy seeds. If several low dose rate brachytherapy seeds have been introduced into the person 1, wherein some of the low dose rate brachytherapy seeds are located in the region 3 and some other low dose rate brachytherapy seeds are not located in the region 3, the spatially confined heating in the region 3 can ensure that only the low dose rate brachytherapy seeds within the region 3 emit substantial radiation.

A corresponding energy application method for applying energy to an object by using the energy application system described above is a low dose rate brachytherapy method, which modifies the energy, which is applied to the person 2 by using the radioactive unit 10 emitting radioactive radiation, by switching the switching unit of the low dose rate brachytherapy seed 6 of the energy application system, wherein the switching unit is switched by generating the magnetic field outside of the person 1 , which traverses the person 1 for reaching the low dose brachytherapy seed 6. In particular, the low dose rate brachytherapy seed is heated such that radioactive isotopes dissolve into the dissolve material 12, in order to allow at least parts of the radioactive unit 10 to pass the shielding elements 11.

Although in the embodiment described above with reference to Figs. 1 to 3 the generated field is a magnetic field, which is used for heating the low dose rate brachytherapy seed in a spatially confined region 3 within the person 1 , in another embodiment the field generating device can also be adapted to generate another field for heating the low dose rate brachytherapy therapy seed. For instance, the field generating device can be adapted to generate an electrical, ultrasonical, electromagnetical or optical field for heating the low dose rate brachytherapy seed, wherein the low dose rate brachytherapy seed comprises a material being heatable by the respective field or wherein the low dose rate brachytherapy seed is indirectly heatable, wherein the respective field is used for heating the surrounding of the low dose rate brachytherapy seed and wherein this heat is then transferred to the low dose rate brachytherapy seed. For instance, the field generating device can be a focused ultrasound device for heating the spatially confined region 3 within the person 2 by focused ultrasound, wherein all low dose rate brachytherapy seeds within this spatially confined region 3 can indirectly be heated by the heat generated in the tissue within this region 3.

The field generating device 4, for instance, the respective magnetic device or ultrasound device, may also be adapted to image the person 1, in particular, the region 3, in order to determine the location of the region 3 within the person 1. Alternatively or in addition, a further imaging device like a computed tomography imaging device, a magnetic resonance imaging device, a nuclear imaging device like a positron emission tomography imaging device or a SPECT device may be used for imaging the region 3 for determining the location of the region 3 within the person 1. The field generating device is then preferentially adapted to switch the low dose brachytherapy seeds from a first mode, in which less energy is applied or in which no energy at all is applied, to a second mode, in which more energy is applied, only if the respective energy application devices are located within the determined region 3. For instance, ultrasound can be focused onto this region 3.

Although above certain configurations of the low dose rate brachytherapy seed have been shown, the low dose rate brachytherapy seed can also have another configuration, which comprises a radioactive unit for emitting radioactive radiation for applying the energy to the person and a switching unit for modifying the energy applied to the person, wherein the switching unit is adapted to be switchable by a field generated outside of the person and traversing the person for reaching the low dose brachytherapy seed. For instance, as schematically and exemplarily shown in Fig. 4, the low dose rate brachytherapy seed 106 can comprise an additional soft magnetic material 113, 115 for concentrating a magnetic flux provided by a magnetic device being, in this example, the field generating device for heating the dissolve material and thereby modifying the energy applied to the person 1. The soft magnetic material 113, 115 may be attached to the magnetic shell 8 via a plastic interface 114, which may be glued to the magnetic shell 8 and the soft magnetic material 113, 115. The whole assembly schematically and exemplarily shown in Fig. 4 is rod-like and has preferentially a diameter below 100 μιη such that it cannot block vessels having a diameter of 100 μιη or larger. The low dose brachytherapy seed with the additional soft magnetic material can also have other longish shape. It is preferentially dimensioned such that it fits into a tube having a diameter of 100 μιη and having an infinite length.

A further possible configuration of a low dose rate brachytherapy seed is schematically and exemplarily shown in Fig. 5. The low dose rate brachytherapy seed 206 schematically and exemplarily shown in Fig. 5 allows for an arbitrary switch by using a technique similar to the technique used by electrophoretic displays ("E-ink"). Also in this case the low dose rate brachytherapy seed 206 can be activated by using a spatially confined magnetic field as used by magnetic particle imaging.

In particular, the low dose rate brachytherapy seed 206 can be reversibly switched between a first mode, in which more energy is applied to the respective object, and a second mode, in which less energy is applied to the respective object, by generating the field accordingly. In particular, the first mode is preferentially a mode, in which energy is applied, and the second mode is preferentially a mode, in which energy is not applied, such that the first mode can be regarded as being an active mode and the second mode can be regarded as being an inactive mode.

The low dose rate brachytherapy seed 206 comprises a coil 213 with a magnetic core 214, wherein the coil 213 is electrically connected with the magnetic core 214 via a wire 215. The low dose rate brachytherapy seed 206 further comprises a first region 205 surrounded by a first material 203 shielding the radioactive radiation emitted by the radioactive unit 210 more and a second region 204 surrounded by a second material 202 shielding the radioactive radiation emitted by the radioactive unit 210 less, wherein the switching unit is adapted such that the radioactive unit 210 is movable from the first region 205 to the second region 204 and vice versa in dependence of the generated field being, in this embodiment, a magnetic field. The first material 203 is, for instance, gold and the second material 202 is, for example, plastic. In this embodiment the radioactive unit 210 is palladium- 103. Within the first material 203 and the second material 202 a channel 217 with an electrophoretic fluid is present, wherein within this electrophoretic fluid the radioactive unit 210 is located. The side wall of the channel 217 is electrically insulated from the first material 203 by an insulator 216, which can be a plastic insulator. An opposite end of the channel 217 comprises an electrical contact 218 like a platinum contact. The contact 218 is electrically connected with the coil 213 via an electrical non- linear device 211. The electrical non-linear device 211 is adapted to transform an AC voltage provided by the coil 213 into a DC voltage with different polarity, i.e. the polarity of the DC voltage provided by the nonlinear device 211 can be switched, wherein in one polarity the radioactive unit 210 is in the first region and in the other polarity the radioactive unit 210 is in the second region.

The coil 213 with the magnetic core 214 is used for generating the AC voltage by using the magnetic device described above with reference to Figs. 2 and 3. The non- linear device 211 is adapted to convert the AC voltage into DC voltage having different polarity depending on the amplitude of the AC voltage. For this reason the non-linear device 211 preferentially comprises, for instance, a first diode with a resistor in a first direction and in parallel two diodes in another direction without resistor. If the amplitude of the AC voltage provided by the coil 213 with the magnetic core 214 is relatively small, the current flows in the direction of the single diode and, if the amplitude of the AC voltage is larger, the current may flow in the other direction with the two diodes, which do not comprise the additional resistor.

In order to allow the radioactive unit 210 to be moved within the electrophoretic fluid the radioactive unit 210 preferentially comprises a surface charge or the radioactive unit is positively charged due to the radioactivity.

The coil 213 with the magnetic core 214, the electrical non- linear device 211, the first material 203, the second material 202 with the channel 217 comprising the electrophoretic fluid and the electrical contact 218 allow for a switching of the low dose brachytherapy seed 206 by moving the radioactive unit 210 from the first region 205 to the second region 204 and vice versa. These components form therefore a switching unit of the low dose brachytherapy seed 206.

Fig. 6 shows schematically and exemplarily a further embodiment of a low dose brachytherapy seed. The low dose brachytherapy seed 306 is adapted to be heatable by the external field, wherein the switching unit comprises a biased spring 301, which is attached to the radioactive unit 310 and which is embedded in a spring holding material 307 adapted to hold the spring 301 in its biased state, if the temperature of the spring holding material 307 is below a spring holding temperature, and to allow the spring 301 to relax, if the temperature of the spring holding material 307 is above the spring holding temperature, wherein the switching unit is adapted such that the radioactive unit 310 is in a first region 305, if the temperature of the spring holding material 307 is below the spring holding temperature, and in a second region 304, if the temperature of the spring holding material 307 is above the spring holding temperature. Also in this embodiment the first region 305 is surrounded by a first material 303, which shields the radioactive radiation and which may be, for instance, gold, and the second region 304 is surrounded by a second material 302, which does not shield the radioactive radiation and which may be a plastic material. The spring holding material 307 is preferentially a meltable material, which is solid below the spring holding temperature and which is liquid above the spring holding temperature. The spring holding material comprises, for instance, paraffin and/or organic substances like a mixture of fatty acids and/or a mixture of metals like lithium, sodium and potassium.

Since the energy applied to the person 1 can be modified by using the spring 301, the spring holding material 307, the first material 303 and the second material 302, these components of the low dose brachytherapy seed can be regarded as forming the switching unit in this embodiment. Moreover, heatable material, which is heatable by the externally generated field and which may be used for directly heating the low dose brachytherapy seed, may be regarded as being an element of the switching unit. However, the seed may also indirectly be heatable by the externally generated field, for instance, by using focused ultrasound for heating the surrounding tissue, wherein the heat of the surrounding tissue is transferred to the seed.

Fig. 7 shows schematically and exemplarily a further embodiment of a low dose rate brachytherapy seed. The low dose rate brachytherapy seed 406 comprises a switching unit including a first region 405 surrounded by a first material 403 having a smaller atomic number and a second region 404 surrounded by a second material 402 having a larger atomic number, wherein the switching unit is adapted such that the radioactive unit 410 is movable from the first region 405 to the second region 404 in dependence of the generated field. In this embodiment the radioactive unit 410 is sulfur-35 or another low energy beta emitter. If the radioactive unit 410 is in the second region bremsstrahlung having a relatively large intensity is generated because of the relatively high atomic number of the second material and, if the radioactive unit 410 is in the first region, bremsstrahlung having a relatively small intensity is generated only, because the first material has a relatively small atomic number. The bremsstrahlung generated, if the radioactive unit 410 is in the second region 404, can then be used to apply the energy to the person 1. Thus, in this embodiment the radioactive radiation is indirectly used for applying the energy to the person 1. The first material having a relatively small atomic number can comprise and can be, for instance, diamond. The second material having the relatively high atomic number can be, for instance, uranium.

The radioactive unit 410 is moved from the first region 405 to the second region 410 similar to the movement of the radioactive unit described above with reference to Fig. 6. Thus, also in this embodiment a biased spring 401 and a spring holding material 407 are used, wherein the biased spring 401 is embedded in the spring holding material 407, which is adapted to hold the spring 401 in its biased state, if the temperature of the spring holding material 407 is below a spring holding temperature, and to allow the spring 401 to relax, if the temperature of the spring holding material 407 is above the spring holding temperature, wherein the switching unit is adapted such that the radioactive unit 410 is in the first region 405, if the temperature of the spring holding material 407 is below the spring holding temperature, and in the second region 404, if the temperature of the spring holding material 407 is above the spring holding temperature.

Since in this embodiment the energy applied to the person 1 can be modified by using the spring 401, the spring holding material 407, the first material 403 and the second material 402, these components of the low dose brachytherapy seed can be regarded as forming the switching unit. Moreover, also in this embodiment heatable material, which is heatable by the externally generated field and which may be used for directly heating the low dose brachytherapy seed, may be regarded as being an element of the switching unit.

However, the seed may also indirectly be heatable by the externally generated field, for instance, by using focused ultrasound for heating the surrounding tissue, wherein the heat of the surrounding tissue is transferred to the seed.

In a further embodiment the low dose brachytherapy seed 406 can comprise an outer shielding enclosing the first and second materials 403, 402. The shielding can have a relatively small atomic number. Preferentially, the shielding has a weighted average atomic number being smaller than or equal to 10, wherein the weighted average Z can be determined in accordance with following equation:

7 = _i (1)

∑c,Z,

i In this equation Z. is the atomic number of the i -th element and c. is the concentration of the i -th element, wherein the shielding material may comprises one or more elements. The concentration c. may be defined as the number of atoms of the respective element relative to the weight, the amount in mol, the volume or another quantity describing the amount of the entire shielding material.

Referring again to Fig. 1, the energy application system further comprises a monitoring device 30 for detecting the energy applied by the energy application device for monitoring the application of energy. In particular, the monitoring device 30 can be adapted to detect the distribution of the applied energy within the object. The monitoring device 30 can comprise a SPECT system for detecting the energy and for determining the distribution depending on the detected energy. The monitoring device 30 can also be adapted to detect the switching state of the energy application device, especially the distribution of the switching states, if several energy application devices have been introduced into the person 1. For instance, if the energy application device 206 schematically and exemplarily shown in Fig. 5 is used and if the radioactive unit 210 is close to the electrical contact 218, which is preferentially a platinum electrode, characteristic x-rays will be generated, which indicate that the respective energy application device 206 is active and which may be detected by the monitoring device 30. The field generating device 4 can be adapted to control the generation of the field depending on a monitoring result provided by the monitoring device 30, especially in accordance with a predefined dose prescription.

Brachytherapy is a method for treating tumors by inserting a radiation source into tumor tissue. Brachytherapy has the potential to deliver a very high dose to the tumor tissue, while surrounding tissue is not harmed much. The brachytherapy can be performed in a high dose rate variant and in a low dose rate variant. In the high dose rate variant a very high activity seed is inserted for a short time period of time and then withdrawn. In the low dose rate variant radioactive seeds are permanently implanted.

The main problem with low dose rate brachytherapy is the placement of the low dose rate brachytherapy seeds. In cases, in which the low dose rate brachytherapy is applied, it is generally difficult to reach the tumor region, because otherwise the tumor would be removed in a surgical procedure. The placement of the low dose rate brachytherapy seeds is therefore, as already mentioned above, often problematic. An elegant way for placing the low dose rate brachytherapy seeds could be the infusion of the seeds into the tumor region with the blood stream as it is done in a transarterial chemoembolization (TACE) like procedure known in the field of treating liver tumors. The main problem with this method is that usually not all seeds will be placed in the tumor region. Even a single seed, which is not placed in the tumor region, may cause intolerable side effects in vulnerable tissue like bladder tissue. Moreover, the seeds should not have a diameter larger than 100 μιη, because seeds of this size may block vessels and thereby cause significant side effects like pain.

The energy application system described above is therefore adapted to use low dose rate brachytherapy seeds that do not deliver a significant dose to the tissue, if not activated. The low dose rate brachytherapy seeds can be activated by an external influence, wherein the activated low dose rate brachytherapy seeds deliver a high dose. The activation is preferentially locally confined such that only low dose rate brachytherapy seeds within a tumor site are activated. The switching between an inactive state and an active state can be performed by a physical movement of radioactive isotopes, i.e. a radioactive unit, within the low dose rate brachytherapy seed. The low dose rate brachytherapy seed preferentially comprises a material that effectively shields the radiation of the radioactive isotopes. If the radioactive isotopes are moved to the surface of the low dose brachytherapy seed, the shielding effect is diminished, in particular, disappears, and the surrounding tissue is irradiated.

Although in above described embodiments the energy application system is a low dose rate brachytherapy system for applying energy to tumors, in particular, to solid tumors, in other embodiments the energy application system can also be adapted to provide energy to another object like another kind of tissue within a living being or to an inner part of a technical object.

Although in above described embodiments certain fields like a magnetic field and a focused ultrasound field have been described, in other embodiments other fields can be used for switching the switching unit of the energy application device like optical fields, electromagnetic fields, et cetera. The energy application device, in particular, the low dose rate brachytherapy seed, is preferentially dimensioned such that it can be located within a tube having a diameter of 100 μιη and having an infinite length.

Although in the embodiments described above with reference to Figs. 6 and 7 a spring force has been used for moving a radioactive unit from a first region to a second region, in other embodiments other forces can be used for moving the radioactive unit like magnetic forces. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended 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 unit or device may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

The control of the field generating device in accordance with the above described energy application method can be implemented as program code means of a computer program and/or as dedicated hardware.

A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium, supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.

The invention relates to an energy application system for applying energy to an object, particularly to a low dose rate brachytherapy system. The system includes an energy application device, which is preferentially a seed to be introduced into the object and which comprises a radioactive unit for applying the energy and a switching unit for modifying the energy applied to the object, wherein the switching unit is adapted to be switchable by a field like a magnetic or ultrasound field generated outside of the object. By using this energy application device it can be switched, in particular, activated, from the outside of the object, only if it has reached a desired location within the object, to which energy should really be applied. This allows for an improved accuracy of applying energy to the object.

Claims

CLAIMS:

1. An energy application system for applying energy to an object (1), the energy application system comprising:

an energy application device (6; 106; 206; 306; 406) to be introduced into the object (1), the energy application device (6; 106; 206; 306; 406) comprising a radioactive unit (10; 210; 310; 410) for emitting radioactive radiation for applying the energy and a switching unit (8, 11, 12; 202, 203, 211, 213, 214, 217, 218; 301, 302, 303, 307; 401, 402, 403, 407) for modifying the energy applied to the object (1), wherein the switching unit is adapted to be switchable by a field generated outside of the object (1) and traversing the object for reaching the energy application device (6; 106; 206; 306; 406),

- a field generating device (4) for generating the field.

2. The energy application system as defined in claim 1, wherein the switching unit is adapted to be switchable by a magnetic field and/or an ultrasound field.

3. The energy application system as defined in claim 1, wherein the switching unit is adapted to switch the energy application device (6; 106; 206; 306; 406) from a first mode to a second mode, wherein in the second mode more energy is applied to the object (1) than in the first mode, wherein the field generating device (4) is adapted to generate the field such that the energy application device (6; 106; 206; 306; 406) is switchable from the first mode to the second mode in a spatially confined region only.

4. The energy application system as defined in claim 1, wherein the energy application device (6; 106; 306; 406) is adapted to be heatable by the field, wherein the switching unit is adapted to be switchable depending on heat.

5. The energy application system as defined in claim 4, wherein the switching unit comprises shielding elements (11) for shielding the radioactive radiation emitted by the radioactive unit (10) and a dissolve material (12), in which the radioactive unit (10) is dissolvable, if heated above a dissolve temperature, wherein the shielding elements (11) are distributed within the dissolve material (12) and wherein the switching unit is adapted such that the energy application device (6) is switchable between a first mode, in which the temperature of the dissolve material (12) is below the dissolve temperature and in which the dissolve material (12) with the distributed shielding elements (11) encloses the radioactive unit (10), and a second mode, in which the temperature of the dissolve material (12) is above the dissolve temperature and the radioactive unit (10) is dissolved in the dissolve material (12).

6. The energy application system as defined in claim 1, wherein the switching unit comprises a first region (205; 305) surrounded by a first material (203; 303) shielding the radioactive radiation emitted by the radioactive unit (210; 310) more and a second region (204; 304) surrounded by a second material (202; 302) shielding the radioactive radiation emitted by the radioactive unit (210; 310) less, wherein the switching unit is adapted such that the radioactive unit (210; 310) is movable from the first region (205; 305) to the second region (204; 304) in dependence of the generated field.

7. The energy application system as defined in claim 6, wherein the energy application device (306) is adapted to be heatable by the field, wherein the switching unit comprises a biased spring (301), which is attached to the radioactive unit (310) and which is embedded in a spring holding material (307) adapted to hold the spring (301) in its biased state, if the temperature of the spring holding material (307) is below a spring holding temperature, and to allow the spring (301) to relax, if the temperature of the spring holding material (307) is above the spring holding temperature, wherein the switching unit is adapted such that the radioactive unit (310) is in the first region (305), if the temperature of the spring holding material (307) is below the spring holding temperature, and in the second region (304), if the temperature of the spring holding material (307) is above the spring holding temperature.

8. The energy application system as defined in claim 6, wherein the radioactive unit (210) is adapted to be movable by an electrical field, wherein the switching unit is adapted to generate an electrical field for moving the radioactive unit (210) from the first region (205) to the second region (204) depending on the field generated by the field generating device (4).

9. The energy application system as defined in claim 1, wherein the switching unit comprises a first region (405) surrounded by a first material (403) having a smaller atomic number and a second region (404) surrounded by a second material (402) having a larger atomic number, wherein the switching unit is adapted such that the radioactive unit (410) is movable from the first region (405) to the second region (404) in dependence of the generated field.

10. The energy application system as defined in claim 1, wherein the energy application system further comprises a monitoring device (30) for detecting the energy applied by the energy application device for monitoring the application of energy.

11. An energy application device for being used in an energy application system as defined in claim 1, wherein the energy application device (6; 106; 206; 306; 406) is adapted to be introduced into the object (1), the energy application device (6; 106; 206; 306; 406) comprising a radioactive unit (10; 210; 310; 410) for emitting radioactive radiation for applying the energy and a switching unit for modifying the energy applied to the object (1), wherein the switching unit is adapted to be switchable by a field generated outside of the object (1) and traversing the object for reaching the energy application device (6; 106; 206; 306; 406).

12. A field generating device for being used in an energy application system as defined in claim 1 , wherein the field generating device (4) is adapted to generate a field being adapted to switch a switching unit of an energy application device (6; 106; 206; 306; 406) of the energy application system for modifying the energy applied to an object (1).

13. A monitoring device for monitoring an application of energy performed by an energy application system as defined in claim 1 , wherein the monitoring device is adapted to detect the energy applied by the energy application device of the energy application system.

14. An energy application method for applying energy to an object (1) by using the energy application system as defined in claim 1, the energy application method comprising modifying the energy, which is applied to the object (1) by using a radioactive unit (10; 210; 310; 410) emitting radioactive radiation, by switching a switching unit of an energy application device (6; 106; 206; 306; 406) of the energy application system, wherein the switching unit is switched by generating a field outside of the object (1), which traverses the object (1) for reaching the energy application device (6; 106; 206; 306; 406).

15. An energy application computer program for applying energy to an object (1) by using the energy application system as defined in claim 1 , the energy application computer program comprising program code means for causing an energy application system as defined in claim 1 to carry out the steps of the energy application method as defined in claim 14, when the computer program is run on a computer controlling the spatial arrangement modifying device.