Patent Description:
Hyperthermia treatment is a method used for treating tumour cells by exposing body tissue of cancer patients to temperatures in the range of <NUM>-<NUM>. Hyperthermia stimulates blood perfusion leading, e.g., to a more effective delivery of drugs in tissues and the presence of more oxygen and, hence, the creation of more oxygen-radicals by ionizing radiation. Hyperthermia also sensitizes tissues to these DNA damaging agents in multiple ways, e.g. through blocking DNA damage repair. Healthy tissue can remain undamaged during hyperthermia treatment up to a temperature of <NUM> for up to an hour. The high temperature that is required for hyperthermia treatment is induced by exposing the patient's body tissue to electromagnetic waves.

While the tumour cells are being heated, the electromagnetic waves may cause skin burns on a patient's skin. Furthermore, electromagnetic waves may be hard to guide to the correct place inside the patient's body. To tackle these issues, a layer with water, a water bolus, is placed between electromagnetic wave generators and the skin of the patient as a cooling agent to prevent burns from the radiated heat and as a transferring agent for the electromagnetic energy. The electromagnetic waves typically have a frequency between <NUM> and <NUM>.

Known water boluses are formed as balloons through which water may be circulated. One side of the water bolus is arranged for skin contact, and preferably the contact between water bolus and skin is as good as possible meaning that no air gaps between the water bolus and the skin are desired. The fully water-filled water bolus, however, does not provide a reliable skin contact, as for example folds or sharp wedges occur at the patient side of the water bolus which creates undesired air gaps between the patient's skin and the water bolus. At the site of the wedges the shape change may induce high concentration of the electromagnetic field resulting in local high heating and a toxicity risk to the patient. Next to the high heating, the wedges result in a poorly cooled region which in combination with the heating poses a high risk for burns.

Furthermore, the fully water-filled water bolus presses onto the body part of the patient that is being treated due to the weight and pressure of the water inside the water bolus. This pressing may be experienced as uncomfortable, for example when the body part is the patient's head, face or neck. <CIT> discloses the use of a foam insert, provided inside the water bolus. This foam insert increases the shape stability and decreases the amount of undesired folds at the patient side of the water bolus. Any insert has the disadvantage that it decreases the volume percentage of water in the water bolus which may decrease the volume averaged dielectric value and hence the guidance of the electromagnetic or acoustic energy. Open-cell polyether foam is therefore used since it provides a low filling percentage, and hence allows most of the available volume inside the water bolus to be filled with water. The open cell structure of the foam further allows water to flow easily through the insert and thus through the water bolus which is beneficial for effectively cooling the patient's skin and obtaining a more uniform water temperature within the water bolus.

A water bolus is provided with among others an even more improved shape stability.

Although the open-cell foam insert improved shape stability, still unpredictable folds are prone to occur at the patient's skin side of the water bolus. These folds block water circulation locally and inhibit prevention of temperature hotspots on the patient's skin. Furthermore may an increased shape stability of the water bolus provide a better match between a software simulation of the hyperthermia treatment and the real-world situation. Software simulation may be used for planning of the treatment.

A water bolus for covering part of an outer body surface of a body part is provided, comprising a flexible cover forming a container arranged for containing a fluid and an insert provided inside the container, wherein the insert is arranged to provide a first stiffness in a first load direction and a second stiffness in a second load direction, wherein the first stiffness is lower than the second stiffness, and a cover stiffness of the flexible cover is lower than the first stiffness. In an embodiment, the first load direction is perpendicular to the second load direction.

With stiffness, in this description the property is meant of how an object resists deformation under a certain force. The stiffness may be expressed in N/mm, i.e. the amount of force required to deform the object over a certain distance. The stiffness may depend on the material of which an object is made, on the shape of the object, on the wall thickness of the object and in what direction the force is applied on the shape of the object. The insert according to the present invention provides, other than the known open-cell foam inserts, a different stiffness in different load directions. The opposite to stiffness is compliance, i.e. the property of how an object complies to deformation under a certain force.

The open cell foam insert known in the art provides substantially the same stiffness in every load direction, and also substantially the same stiffness no matter where the force is applied because of the structure of an open-cell foam. That structure consists of cells which are not completely encapsulated, which is required for allowing water to flow through the insert.

In the first load direction, more compliance may be required, for example to ensure a good fit between the patient's skin and the water bolus. In the second load direction, more stiffness may be required, for example to resist against shape instability of the water bolus due to the weight and pressure of the water inside the water bolus or to resist against external loads on the water bolus, e.g. handling by the user. The flexible cover which forms the container is generally more compliant than the insert, which means that the shape of the insert pre-dominantly determines the shape of the container and the shape of the flexible cover adapts to the shape of the insert.

In many configurations, the water bolus will have an overhanging part, which is a part which in use is a higher part hanging over a lower part. The higher part will have a tendency to, when the water bolus is filled with water, deform towards the lower part. In use, a patient's head may be present between the lower part and the higher part, and thus the higher part may press into the face of the patient which may be perceived as an uncomfortable pressing. A higher stiffness of the insert against this overhanging may increase the comfort of the patient by reducing the deformation of the higher part towards the lower part and thus relieving pressure on the patient's head. More in general, because the container comprises a flexible cover, the container is prone to sagging when filled with water due to water pressure and weight elastically deforming the flexible cover.

With open cell foam inserts, a single stiffness for all load directions has been chosen due to the isotropic stiffness of the open cell foam material. This leads to either a non-optimal first stiffness in a first load direction, a non-optimal second stiffness in a second load direction, or a compromise between the two stiffnesses resulting in neither an optimal first stiffness nor an optimal second stiffness. A water bolus with an insert with anisotropic stiffness is provided.

At least part of an inner surface of the insert may be substantially complementary to at least part of the outer body surface and the first load direction may be for a substantial part of the inner surface substantially oriented normal to the inner surface of the insert. With the at least part of the inner surface of the insert being complementary to the at least part of the outer body surface, the water bolus is pre-shaped to fit with the outer body surface, which decreases the odds of the undesired folds in the water bolus at the patient's side of the water bolus.

The complementariness of the inner surface of the insert and the outer body surface may result in a small deviation in correspondence between the inner surface of the insert and the outer body surface. The water pressure inflating the container may be used for compensating for the small deviation.

To provide the first stiffness in the first load direction and the second stiffness in a second load direction, the insert may comprise a plurality of linked, thin-walled, elongated, parallel, hollow structures.

The structures are linked for allowing forces to be transferred directly between adjacent structures, and as such for example buckling may be prevented. The structures are thin-walled for minimising the volume of the insert inside the water bolus, which maximises the possible volume of water inside the water bolus. The structures are elongated for allowing an elongated flow-path through the structures, and parallel for having the flowpaths substantially parallel to one another. The structures are hollow to allow a water flow through the structures from one end to the other end.

Within the water bolus, a certain dielectric constant may be preferred. This dielectric constant may be preferred to be relatively high as it may be matched with the electromagnetic frequencies used by a certain hyperthermia device. Additionally or alternatively, the dielectric constant may be matched to a dielectric constant of the body of the patient. To obtain the desired dielectric constant, a certain insert volume to water ratio may be chosen to obtain said desired dielectric constant.

Furthermore, the dielectric constant may differ in different sections of the water bolus, for example by locally adjusting the ratio of insert volume to water volume. The material of which the insert is made typically has a lower dielectric constant than water, and this property may hence be used to at least locally lower the dielectric constant as observed by electromagnetic waves passing through the water bolus towards the patient. Local adjustments to the dielectric constant may for example be made by locally adjusting a wall thickness of the insert. A preferred dielectric constant may be calculated or determined before manufacturing the insert, for example using computer simulation, and as such a specialised insert may be made for a specific case or patient.

When the insert comprises the plurality of linked, thin-walled, elongated, parallel, hollow structures, the second load direction may be oriented substantially parallel to an elongation direction of the hollow structures and the first load direction is substantially perpendicular to the elongation direction of the hollow structures.

In an embodiment of the water bolus, the hollow structures are arranged as elongated hexagonal structures, also known as honeycomb structures. As the name already implies, the honeycomb structure is inspired by the way bees build their beehive to provide enough strength yet as much space as possible for their honey. The hexagonal architecture eliminates unnecessary material which enables a small filling percentage of structure material and a large filling percentage of water inside the water bolus. This ensures a limited influence of material on the electromagnetic waves.

When the inserts are arranged as elongated hexagonal structures, the insert may be arranged to provide a third stiffness in a third load direction, wherein the third load direction is oriented substantially perpendicular to an elongation direction of the hollow structures and at an approximately <NUM> degree angle relative to the first load direction, and wherein the third stiffness may be higher than the first stiffness. Alternatively, for example by manipulating wall thicknesses of some or all walls of one or more structures, or by manipulating the cross-section of one or more structures, the third stiffness of the insert may be lower than the first stiffness, as will be appreciated by a person skilled in the art. The three load directions may thus be orthogonal relative to each other.

In use of the water bolus, the third load direction may be a substantially vertical direction, and the first load direction may be a substantially horizontal direction.

The container may comprise a fluid input for receiving a fluid and a fluid output for releasing a fluid such that a fluid flow may be provided within the container between the fluid input and the fluid output. Between the fluid input and the fluid output, though the water bolus, a fluid flow may be established. Such a flow allows a better regulation of the fluid temperature in the water bolus, more specifically a more homogenous fluid temperature. The homogenous fluid temperature may be most desired at or near the skin of the patient, and the insert design may be adjusted to optimize a fluid flow arranged for providing this homogenous fluid temperature at or near the skin of the patient.

The preferred fluid is water, but other fluids may also be used in the water bolus. Water has the advantages of being cheap and broadly available, having good thermal properties, and being non-toxic. Depending for example on the desired dielectric constant of the water bolus or sections thereof, different fluids may be chosen.

A first of the fluid input and the fluid output may be provided at a first side of the flexible cover, and a second of the fluid input and the fluid output may be provided by a fluid conduit substantially extending from the first side to a second side of the flexible cover opposite to the first side.

With this configuration of the fluid input and the fluid output, both may be provided on the same side of the water bolus whilst maintaining a good water flow through the entire water bolus.

When the second of the fluid input and the fluid output is provided by the fluid conduit, the fluid conduit may extend through the container and thus not outside the container. This may provide a compact form-factor of the water bolus, and both at the patient side and the device side there is no room for extending the fluid conduit outside the water bolus.

At least some of the plurality of hollow structures may comprise a plurality of perforations such that hollow interiors of adjacent hollow structures provided with the perforations are in fluid communication with one another. This allows not only a separate fluid flow through each individual elongated structure, but also a fluid flow between adjacent structures. This may increase the homogeneity of the water temperature inside the water bolus.

The water bolus fluid may be arranged to have fluid flowing within the water bolus from the first side to the second side and a flow-through surface of the perforations may substantially increase from the first side to the second side.

To be able to measure the pressure applied on the patient's skin, a pressure sensor can be inserted inside the water bolus. Based on the measured pressure, the water volume inside the bolus can be increased or decreased.

The water bolus may be arranged for transferring electromagnetic energy through the water bolus, for example when the water bolus is to be used in hyperthermia treatment.

A wall thickness of the hollow structures may increase dependent on expected fluid pressures inside the water bolus. This allows a further optimization of the volume occupied by the insert inside the water bolus. Not everywhere is the same wall thickness required, since the forces due to water pressure will increase in a direction opposite to gravity.

When the water bolus is arranged for a fluid flow within the water bolus from the first side to the second side, perforations may be spaced apart, and an average distance between adjacent perforations may increase from the first side to the second side.

When the structures comprise multiple perforations, a first perforation may be provided out of register with a second perforation relative to the direction of elongation. This may provide a flow path through the perforations with enhanced thermal properties for the water bolus.

The various aspects and embodiments thereof will now be discussed in conjunction with drawings. In the drawings:.

Different embodiments of the present invention will be explained in more detail based on an example of a use of the water bolus in hyperthermia treatment. Different applications for the water bolus are envisioned as well, as will be discussed further onwards in this description.

One of the most difficult areas to reach with hyperthermia treatment is the head and neck region, and the figures will therefore be directed towards embodiments of a water bolus for use in hyperthermia treatment for head, neck, and/or larynx. It will be appreciated by a person skilled in the art that different applications of the water bolus for different body parts are also envisioned, and thus that the water bolus may be shaped differently than shown in the figures. For example, a water bolus for use in treatment in the head region may span a distance between the eyes and the chin of a patient. In another example, a water bolus for use in treatment in the neck region may span a distance between the eyes and the collarbone of the patient. The height of the water bolus may for example reach from the back of the head of the patient up to the height of the eye level of the patient. In yet another example, the water bolus may be shaped complementary to one or more other body parts, such as a skull, a belly, at least part of a leg, at least part of a pelvic area, breasts, any other body part, in particular curved body part, or any combination thereof. A shaped water bolus may be pre-shaped such that a desired shape is achieved after filling the water bolus with water. Computer calculations and/or simulations may be used for determining the shape of the water bolus in a situation without water, and in a situation wherein the water bolus has been filled with water. The position and/or orientation in which the water bolus will be used may be taken into account as well, as gravity may affect the shape of the water bolus.

The main aims of the water bolus are as discussed the transferring of electromagnetic waves to the patient's tissue, and preventing skin burns on the patient's skin due to heating caused by these electromagnetic waves. It is further an aim of the water bolus to assist in maintaining a position and/or orientation of the head of the patient during the treatment.

Next to being more comfortable for patients, the water bolus according to the present invention may be more easily useable by an operator of a hyperthermia device who has to handle the water bolus because of the increased stiffness in certain load directions. The more easy useability may result in one or more of: a higher reproducibility of the hyperthermia treatment between different treatment settings, a better transfer of predicted energy patterns to the patient, and a better treatment outcome. Furthermore may a faster set-up of the hyperthermia device be achieved, which may save time and enhance acceptance of the treatment by the patient.

<FIG> shows a top view of part of a hyperthermia device <NUM> with part of a patient <NUM> lying inside the device <NUM>. The hyperthermia device <NUM> comprises two separate water boluses: a left water bolus <NUM> and a right water bolus <NUM>, with left and right as seen by the patient. The left water bolus <NUM> is arranged for covering part of an outer surface of a head <NUM>, a neck <NUM> and a larynx <NUM> as outer body surfaces of body parts. The right water bolus <NUM> is arranged for covering an outer surface of the head <NUM> and the neck <NUM> as outer body surfaces of body parts. For conciseness of the description and because the two water boluses function similarly, from here on only the left water bolus <NUM> will be discussed and will be referred to as water bolus <NUM>. The water boluses may be supported by a frame <NUM> comprised by the hyperthermia treatment device <NUM>.

Not shown in the figures are radiation sources comprised by the hyperthermia device <NUM>, wherein the radiation sources are arranged to direct electromagnetic radiation towards the patient through the water bolus <NUM>. In use, the water bolus <NUM> will be provided between the patient's body part, which will receive electromagnetic radiation and the radiation sources.

The water bolus <NUM> comprises a flexible cover <NUM> forming a container <NUM> arranged for containing a fluid such as water, and an insert <NUM> provided inside the container, wherein the insert <NUM> is arranged to provide a first stiffness in a first load direction and a second stiffness in a second load direction, wherein the first stiffness is lower than the second stiffness, and a stiffness of the flexible cover is lower than the first stiffness.

<FIG> shows a front view of the hyperthermia device <NUM> and the back of the head <NUM> of the patient <NUM>. The left water bolus <NUM> and the right water bolus <NUM> surround the head <NUM> and have for clarity of the figure been slightly moved outward away from the head <NUM>. In use, the water bolus <NUM> will be placed in contact with the patient's skin.

<FIG> shows an overhanging part <NUM> of the water bolus <NUM>, which due to the weight of the water inside the water bolus <NUM> will want to collapse in a direction opposite to the gravity g. In <FIG>, the inner shape <NUM> of the insert <NUM> is also visible, which corresponds to an outer body surface.

As can been seen from <FIG>, it is preferred to leave at least some part of the patient's face exposed. This allows the patient to breathe through his nose and/or mouth, and preferably allow the patient's eyes to remain exposed as well. The exposure increases comfort of the patient, and decreases the feeling of being trapped inside a device for the patient.

<FIG> again shows a top view of part of a hyperthermia device <NUM> with part of the patient <NUM> lying inside the device <NUM>. In the embodiment of the water bolus <NUM> as shown in <FIG>, the insert <NUM> comprises a plurality of linked, thin-walled, elongated, parallel, hollow structures <NUM>. In the embodiment of <FIG>, an elongation direction <NUM> of the structures <NUM> is substantially parallel to the length of the patient <NUM> from head to toe. Embodiments of the insert wherein the elongation direction <NUM> is perpendicular to the length of the patient are envisioned as well.

A cross-section of an elongated structure may be constant over the length of the structure, and may have any shape such as a triangle, rectangle, square, circle, hexagonal, any other shape, or any combination thereof. Embodiments of the insert <NUM> comprising elongated structures with different cross-sections are envisioned as well, and the cross-section of one structure need not be constant over the length of the structure.

<FIG> shows a view of the back of the head <NUM> of the patient <NUM>, wherein the head <NUM> is partially surrounded by the water boluses <NUM> and <NUM>. In <FIG>, the elongation direction <NUM> extends into the plane of the paper. The structures <NUM> of the insert <NUM> are in this embodiment hexagonally shaped. The structures <NUM> are in the embodiment of <FIG> provided such that two straight side planes of the hexagonal structures are substantially parallel to the direction of the gravity g. Embodiments of the insert <NUM> wherein the structures <NUM> are rotated <NUM> degrees or any other angle over the elongation direction are also envisioned.

Hexagonal structures <NUM> provide a first stiffness in a first load direction, a second stiffness in a second load direction, and a third stiffness in a third load direction. The first load direction, indicated with <NUM> in detail <NUM> of <FIG>, may be a direction perpendicular to one of the planes comprised by the hexagonal, and may in use be substantially perpendicular to the direction of gravity g. A second load direction may be parallel to the elongation direction <NUM> of the hexagonal structure. The third load direction, indicated with <NUM> in detail <NUM>, may be a direction angled <NUM> degrees relative to the first load direction <NUM> around an axis parallel to the elongation direction <NUM>. This corresponds to a load on the line where two planes of the hexagonal meet.

Depending on the material choice for the structures and the wall thicknesses of the structures, the first stiffness may be lower than the second stiffness, and the third stiffness may be higher than the first stiffness. Using this knowledge, a person skilled in the art may position the structures in the water bolus <NUM> as preferred. For adjusting the stiffness of the insert <NUM> in any direction, a person skilled in the art will appreciate different ways of manipulating properties of the structures such as wall thicknesses, orientation, and cross-sectional shapes to achieve a desired stiffness in a certain direction and/or a ratio between different stiffnesses in different directions.

<FIG> shows part of an embodiment of an insert <NUM> for a water bolus, which insert <NUM> comprises a plurality of linked, thin-walled, elongated, parallel, hollow, hexagonal structures <NUM>. The inner shape <NUM> substantially corresponds to an outer body surface indicated by the dotted contour <NUM>. Because the dotted contour <NUM> may not perfectly correspond to an insert <NUM> shape made out of only full hexagonal structures, some of the structures are only partially provided as partial structures <NUM> with only one, two, three. four or five out of the six possible planes present.

Instead of, or next to, using the partial structures <NUM>, structures <NUM> with different cross-sectional shapes and/or dimensions may be comprised by the insert <NUM>. For example, to follow the shape of the dotted contour <NUM> better, the insert <NUM> may comprise at the side of the inner shape <NUM> structures with a smaller cross-sectional surface. This allows the insert to comprise less partial structures <NUM>, and thus more full structures. Furthermore, for example to follow the shape of the dotted contour <NUM> better, one or more structures <NUM> may comprise a non-constant cross-sectional shape.

Next to a non-constant cross-sectional shape, or as an option on itself, one or more structures <NUM> comprised by insert <NUM> may have a non-constant wall thickness. A locally higher wall thickness may increase the shape stability of the entire insert <NUM>. Keeping this in mind, a person skilled in the art may readily appreciate how to adapt the wall thickness and/or cross-sectional shape of one or more structures <NUM> of the insert <NUM>.

A first structure <NUM> and a second structure <NUM> as adjacent structures share a common plane <NUM> which comprises a perforation <NUM>. By virtue of perforation <NUM>, the first structure <NUM> and the second structure <NUM> are in fluid communication and fluid may flow between the first structure <NUM> and the second structure <NUM> through the perforation <NUM>. Any structure may comprise any number of perforations in any plane of the structure, for example any of the six planes when the structures are shaped as hexagonal structures. Only one perforation <NUM> is shown in <FIG> for clarity an conciseness of the figure.

An embodiment of the insert <NUM> similar to that of the insert <NUM> shown in <FIG> is also envisioned wherein the hexagonal structures <NUM> are rotated <NUM> degrees around the elongation direction <NUM>, i.e. with the flat sides of the hexagonal shape not pointing up and down but left and right. Such an embodiment is shown in <FIG>, which shows a rendering of an embodiment of the insert <NUM>.

The insert of <FIG> comprises a plurality of linked, thin-walled, elongated, parallel, hollow, and hexagonal structures <NUM>. The insert <NUM> further comprises a plurality of perforations <NUM> provided in the structures <NUM>. As can be seen in <FIG>, a large number of perforations <NUM> may be provided on any and all planes of the hexagonal structures <NUM>.

The insert <NUM> may further comprise a fluid inlet <NUM> and a fluid outlet <NUM>. The fluid inlet <NUM> may be used when filling the water bolus <NUM> with a fluid such as water, and the fluid inlet <NUM> may be used for draining the water bolus <NUM>. Both the fluid inlet <NUM> and the fluid outlet <NUM> may be used for water circulation through the water bolus.

When the fluid inlet <NUM> is in use provided lower than the fluid outlet <NUM> relative to the gravity, filling the water bolus with fluid using the fluid inlet <NUM> allows air to escape the water bolus through the fluid outlet <NUM>. While draining the water bolus, gravity will assist the fluid to leave the water bolus through the lower fluid inlet <NUM>.

<FIG> shows a schematic view of part of a hyperthermia device <NUM> to indicate how water as an example of a fluid may flow through embodiments of the water bolus <NUM>. The hyperthermia device <NUM> further comprises a pumping device <NUM> for pumping the liquid through the water bolus <NUM> as a flow of water and an optional temperature regulator <NUM> for controlling a temperature of the water flowing through towards the water bolus <NUM>. The temperature regulator <NUM> may be provided downstream or upstream of the pumping device <NUM>.

For receiving the flow of water the water bolus <NUM> comprises a fluid input <NUM>, and for creating the flow path towards the pumping device <NUM>. The water bolus <NUM> further comprises the fluid output <NUM>. In the embodiment of <FIG>, the fluid input <NUM> and the fluid output <NUM> are provided at the same side of the flexible cover <NUM> of the water bolus <NUM>, which may be a first side.

It is preferred that the fluid flow comprises two directional components: a first flow direction <NUM> substantially corresponding to the elongation direction <NUM> of the structures <NUM>, and a second flow direction <NUM>, perpendicular to the first flow direction <NUM>. Flow in the first flow direction <NUM> is allowed through the hollow structures <NUM>, and flow in the second flow direction <NUM> is allowed through the plurality of perforations <NUM>, indicated with dotted lines.

In the embodiment of <FIG>, a flow-through surface of the perforations <NUM> substantially increases from the first side <NUM> to the second side <NUM>. With this increasing, fluid flow in the second flow direction <NUM> becomes more easy the further the flow is away from the first side <NUM> where the pumping device <NUM> is provided. A more uniform fluid flow inside the water bolus <NUM> may be achieved, and as a result thereof a more uniform temperature distribution inside the water bolus <NUM> may be achieved as well.

Perforations <NUM> of a structure may be aligned with perforations <NUM> of a structure adjacent to it in the second flow direction <NUM>. Alternatively, or additionally, some perforations <NUM> may be shifted, such as the exemplary shifted perforation <NUM>, which is shifted along the first flow direction <NUM> relative to the other perforations <NUM>. As can been seen in <FIG>, this shifted perforation <NUM> is not aligned with the perforations <NUM> of adjacent structures in the second direction <NUM>. Such a misalignment may prevent a direct fluid flow through vertically adjacent perforations <NUM> and increase homogeneity of fluid flow and temperature inside the water bolus <NUM>.

The water bolus <NUM> may be provided with a fluid conduit <NUM> substantially extending from the first side <NUM> to the second side <NUM> of the flexible cover <NUM>. The fluid conduit <NUM> may shift the fluid output <NUM> from the first side <NUM> towards the second side <NUM>. With this shifting, it becomes easier for the fluid flow to reach the second side <NUM> of the water bolus <NUM> with sufficient flow capacity. Although the fluid conduit <NUM> may be provided partially outside the container <NUM>, it is preferred that the fluid conduit <NUM> extends through the container <NUM> for compactness of the water bolus <NUM>.

The embodiment of the part of the hyperthermia device <NUM> as shown in <FIG> substantially corresponds to the embodiment of the part of the hyperthermia device <NUM> as shown in <FIG>. However, in the embodiment of <FIG>, an average distance between adjacent perforations <NUM> decreases from the first side <NUM> to the second side <NUM>. With this decreasing average distance between adjacent perforation <NUM> more flow through area is provided for the fluid flow in the second flow direction <NUM> the further away from the first side <NUM> the fluid flow is. This may also provide a more uniform fluid flow inside the water bolus <NUM>, and as a result thereof a more uniform temperature distribution inside the water bolus <NUM>.

An embodiment of the water bolus <NUM> is also envisioned wherein both the flow through area of the perforations <NUM> increases and the average distance between adjacent perforations <NUM> decreases from the first side <NUM> to the second side <NUM>. This combination may even further provide a more uniform fluid flow inside the water bolus <NUM>, and as a result thereof an even more uniform temperature distribution inside the water bolus <NUM>.

In use, the first side <NUM> may correspond to the side to which the top of the head of the patient is pointing. The second side <NUM>, opposite to the first side, may then correspond to the side of the feet of the patient. In such an embodiment, all fluid conduits may be provided out of sight and out of reach of the patient.

In embodiments of the water bolus <NUM>, the fluid input <NUM> and fluid output <NUM> as shown in <FIG> may be interchanged, and the flow direction may then be opposite to that as described here above.

Embodiments of the insert <NUM> are also envisioned wherein the structures <NUM> are rotated <NUM> degrees relative to the structures <NUM> shown in <FIG>. As a result thereof, the fluid flow in the first flow direction <NUM> is allowed through the perforations <NUM>, and the fluid flow in the second flow direction <NUM> is allowed though the hollow structures <NUM>.

Any of the embodiments of the insert <NUM> may be manufactured using 3D-printing. This manufacturing technique allows for an insert <NUM> design which corresponds at one side to the hyperthermia device and another side to the outer surface of a body part. A 3D model may first be made of the body part, or an average model may be constructed from multiple 3D models. Using such a body model, the inner shape <NUM> of the insert <NUM> may be determined either for a specific patient, or for an average set of patients. When using 3D-printing, CAD models may be used for both the patient models and the insert <NUM> models.

It is also envisioned to print the insert <NUM> and the cover <NUM> simultaneously, optionally as a single part. Different 3D printing techniques known to a person skilled in the art may be used for this purpose, such as using support material which may be soluble, and printing in spiral, spiralizer, or spiral vase mode for printing the cover <NUM>.

Although the embodiments of this description have been directed towards the use of the water bolus in hyperthermia treatment in the head and neck region, other applications even outside hyperthermia treatment are envisioned as well for the water bolus according to the present invention.

Examples of such applications are: temperature regulation, i.e. heating and/or cooling, of outer surfaces of body parts of a human or animal. For example, heating or cooling of the neck using a water bolus according to the present invention may alter the thermoregulation in patients by influencing the temperature in the thalamus. Skin cooling may also reduce the impact of drugs in the skin, and neck heating may stabilise the temperature of a patient during anaesthesia. Also in sports or physiotherapy may the water bolus with increased shape stability be used.

In medical applications other than hyperthermia treatment a water bolus according to the present invention may be placed between medical equipment and a patient.

In summary, during hyperthermia treatment of the head and neck area, a conventional water bolus, used in such treatment for guiding electromagnetic waves and cooling the patient's skin, may collapse onto the patient's face due to the weight and/or pressure of the water inside the water bolus. An insert may be provided inside the water bolus to remedy this, wherein the insert provides additional stiffness and thus resistance against the water's weight and pressure. The insert however should not be too resistant against the shape of the patient, and thus an insert is provided with a first stiffness in a first load direction and a second stiffness in a second load direction, wherein the first stiffness is not equal to the second stiffness.

In the description above, it will be understood that when an element such as layer, region or substrate is referred to as being "on" or "onto" another element, the element is either directly on the other element, or intervening elements may also be present. Also, it will be understood that the values given in the description above, are given by way of example and that other values may be possible and/or may be strived for.

Furthermore, the invention may also be embodied with less components than provided in the embodiments described here, wherein one component carries out multiple functions. Just as well may the invention be embodied using more elements than depicted in the Figures, wherein functions carried out by one component in the embodiment provided are distributed over multiple components.

It is to be noted that the figures are only schematic representations of embodiments of the invention that are given by way of non-limiting examples. For the purpose of clarity and a concise description, features are described herein as part of the same or separate embodiments, however, it will be appreciated that the scope of the invention may include embodiments having combinations of all or some of the features described. The word 'comprising' does not exclude the presence of other features or steps than those listed in a claim. Furthermore, the words 'a' and 'an' shall not be construed as limited to 'only one', but instead are used to mean 'at least one', and do not exclude a plurality.

A person skilled in the art will readily appreciate that various parameters and values thereof disclosed in the description may be modified and that various embodiments disclosed and/or claimed may be combined without departing from the scope of the invention.

Claim 1:
Water bolus (<NUM>, <NUM>) for covering part of an outer body surface of a body part, comprising:
- a flexible cover (<NUM>) forming a container arranged for containing a fluid; and
- an insert (<NUM>) provided inside the container, wherein the insert is arranged to provide a first stiffness in a first load direction and a second stiffness in a second load direction, characterized in that the first stiffness is lower than the second stiffness, and a stiffness of the flexible cover is lower than the first stiffness.