FIELD OF THE INVENTION

The invention relates to the field of radiation therapy. More particularly, the present invention relates to systems for radiating target areas such as skin or assisting therewith and corresponding methods.

BACKGROUND OF THE INVENTION

Radiation therapy, such as for example light therapy, can be beneficial in medical applications like wound healing. It can accelerate and enhance the wound healing process in the phase where new tissue is formed and the wound starts to contract, referred to as new tissue formation phase. It furthermore can assist in controlling the phase wherein new-born tissue becomes mature scar tissue, referred to as tissue remodeling phase by counteracting overproduction of scar tissue, resulting in the formation of a nice scar.

Radiation therapy also is used to treat Psoriasis, which is a skin disease. Psoriasis results in skin cells being produced at a higher rate than normal, creating an over-amount of skin flakes. The overproduction of skin flakes affects the patient in both his social environment as well in his comfort of living. Medical studies comparing different existing methods for treating psoriasis show that light therapy using 311 nm wavelength is the most effective way.

Different systems for performing radiation therapy are known. Top lit plaster systems are known for radiation therapy but suffer from inhomogeneous irradiation. In order to obtain the therapeutic effect for the whole area of the wound, homogeneous irradiation is preferred. This problem is tackled in international patent application WO 2008/017975 describing a particular combination of a plaster device and a radiation device for performing radiation therapy. The plaster comprises a light guide for homogenizing radiation provided to the skin. Radiation emitted from LEDs positioned at the side, i.e. in a side lit radiation- guide configuration, is guided and homogenized through the light guide and directed to the target area of interest.

Because UV cannot only help in the process of curing or healing but also can damage the DNA of healthy cells resulting in skin cancer, local skin treatment will be one of application design constrains. One other major design constrain is wearability. Wearable plasters will reduce the hassle of the treatment and makes it possible to combine treatment with home activities (such as for example sleeping, watching television).

SUMMARY OF THE INVENTION

It is an object of embodiments of the present invention to provide good systems and/or methods for providing radiation to skin. Advantages of embodiments according to the present invention can be the combination of substantially homogeneous irradiation with compactness of the device, resulting in an increased user comfort, and/or providing substantially homogeneous irradiation in a manner safe for the user. The above objective is accomplished by a method and device according to the present invention.

The present invention relates to a plaster for providing radiation to skin, the plaster being adapted for receiving radiation from at least one radiation source positioned so that at least one projection of the at least one radiation source in a direction perpendicular to an outcoupling surface of the plaster lies within the outcoupling surface, the plaster comprising a homogenizer integrated in the plaster for spreading the received radiation so as to homogenize the received radiation, and an outcoupling surface for coupling radiation from said plaster to the skin. It is an advantage of embodiments of the present invention that a compact system can be obtained that at the same time provides good homogeneity of the irradiation on the skin area to be treated. It is an advantage of embodiments according to the present invention that the power density over the treated skin area is substantially equal, resulting in prevention of skin burning and providing optimal treatment of the skin. It is an advantage of embodiments according to the present invention that the plaster is easily wearable.

The homogenizer may comprise at least one optical element for spreading radiation received from the at least one radiation source. The at least one optical element may be a non-spherical optical element.

It is an advantage of embodiments according to the present invention that by using optical elements in between the at least one radiation source and the skin, direct contact between the at least one radiation source and the skin can be prevented, thus avoiding a too high local optical power density. By direct contact, the optical power density could increase e.g. from about 0.5 mW/cm ² to 0.5 W/cm ² , resulting in the risk of creating skin damage.

The plaster may be adapted for direct lit radiation. The at least one optical element may comprise a refracting element. It is an advantage of embodiments of the present invention that providing optical components in the plaster allows reduction of the thickness of the plaster, resulting in an increased user comfort and wearability and at the same time a good efficiency. With a good efficiency there may be meant an efficiency of at least 80%.

The at least one refractive element may comprise at least one recess provided in the plaster having a surface acting as refracting surface for spreading the radiation received from the at least one radiation source. The at least one recess may be spherical or a-spherical or can contain Fresnel structures, diffractive structures or a frosted surface. It is an advantage of embodiments of the present invention that by providing recesses in the plaster, radiation that is coupled into the plaster is coupled out homogeneously through the outcoupling surface.

The at least one refractive element may comprise at least one individual lens adapted for spreading radiation received from the at least one radiation source. It is an advantage of embodiments according to the present invention that the thickness of the plaster can be further reduced while maintaining homogeneity of the outcoupled radiation by providing two refractive surfaces in the form of individual lenses.

The plaster furthermore may comprise a flexible layer on top of the at least one optical element for providing soft contact between the plaster and the skin to be radiated.

The plaster furthermore may comprise spacers in between at least some of the individual lenses for spacing a radiation incoupling surface, also referred to as radiation receiving surface, and the skin to be radiated. It is an advantage of embodiments according to the present invention that an accurate spacing from the incoupling surface to the skin can be obtained, avoiding injury of the skin during use of the plaster.

The plaster may comprise a gradient refractive index material with decreasing refractive index towards the outcoupling surface thus forming the at least one refractive element. Thus, in some embodiments of the present invention, no additional structural optical elements such as (curved) mirrors or conventional lens surfaces are required, but the selection of the materials used results in an improved homogeneity by means of the optimized material properties of the optical element.

The at least one refractive element may comprise a liquid crystal element for inducing a gradient refractive index profile within the plaster.

The optical element may be a reflective element. The plaster may comprise at least one embedded radiation source emitting radiation in a direction opposite to the outcoupling surface and towards the reflective element, for reflecting and spreading the radiation towards the outcoupling surface. It is an advantage of embodiments according to the present invention that the at least one radiation source can be embedded in the plaster material, avoiding the need for further alignment after manufacturing. Alternatively or in addition thereto, the optical element may be a reflective element and the radiation sources may be non-embedded. The at least one radiation source can also emit radiation in a direction towards the outcoupling surface, but via one mirror surface redirect the radiation in a direction opposite to the outcoupling surface and via another mirror surface redirect the radiation towards the outcoupling surface.

The at least one optical element may comprise a phosphor material for emitting converted radiation to the outcoupling surface upon excitation by radiation from the at least one radiation source.

The phosphor material may be furthermore adapted for scattering radiation from the at least one radiation source thus spreading said radiation.

The optical element may comprise a liquid component embedded in a solid flexible component.

The plaster may be adapted for receiving radiation from a plurality of equally spaced radiation sources spaced at a predetermined pitch, wherein the thickness of the plaster may be substantially smaller than the predetermined pitch.

The plaster furthermore may be adapted for use with radiation sources providing radiation at different wavelengths, e.g. using different types of radiation sources, each type providing radiation at a different wavelength or in a different wavelength region or using one type of radiation sources providing radiation at different wavelengths or in different wavelength regions.

The present invention also relates to a system for providing radiation to skin, the system comprising a plaster as described above and at least one radiation source positioned so that its projection perpendicular to the outcoupling surface of the plaster lies within said outcoupling surface. The system may be such that the plaster in combination with the radiation source is adapted for direct lit radiation.

The at least one radiation source may be a plurality of equally spaced radiation sources spaced at a predetermined pitch, wherein the thickness of the plaster may be substantially smaller than the predetermined pitch.

The at least one radiation source may be a plurality of radiation sources, at least some of them differing in emission wavelength. The optical elements used may, in some embodiments, be tuned for the wavelengths used, thus resulting in some embodiments using different optical elements for the plurality of different emission wavelengths used. The present invention also relates to a method for providing radiation to skin, the method comprising:

providing radiation to a plaster from at least one radiation source positioned such that at least one projection of the at least one radiation source in a direction

perpendicular to the outcoupling surface lies within said outcoupling surface,

spreading the thus received radiation for homogenizing the received radiation in the plaster, and

coupling out the radiation from the plaster to the skin.

It is an advantage of embodiments according to the present invention that a compact system can be obtained through direct lit radiation. Due to compactness, the device may be kept as small as possible, so that comfort of the user is high and the system does not substantially reduce normal functioning of the user and is easily wearable.

Particular and preferred aspects of the invention are set out in the accompanying independent and dependent claims. Features from the dependent claims may be combined with features of the independent claims and with features of other dependent claims as appropriate and not merely as explicitly set out in the claims.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic view of an example of a plaster device for a top- lit system for radiation therapy, according to an embodiment of the present invention.

FIG. 2 illustrates a transmission spectrum for Polydimethylsiloxaan, a material that may be used for manufacturing the plaster device according to an embodiment of the present invention.

FIG. 3 illustrates a radiation device used in or with a plaster according to embodiments of the present invention, wherein the plaster is adapted in shape to provide an (a)spherical air gap as homogenizer.

FIG. 4 illustrates a radiation device used in or with a plaster according to embodiments of the present invention, wherein the plaster comprises an a- spherical lens as homogenizer.

FIG. 5 illustrates a radiation device used in or with a plaster according to embodiments of the present invention, wherein the plaster includes a homogenizer comprising a lens with a-spherical incoupling and a-spherical outcoupling surface. FIG. 6 illustrates a plaster with individual lenses according to an embodiment of the present invention.

FIG. 7 and FIG. 8 illustrate irradiance plots of radiation emitted through a plaster without individual lenses (left hand side) and with individual lenses (right hand side), according to an embodiment of the present invention.

FIG. 9 and FIG. 10 illustrate the radiant intensity profiles using a plaster without individual lenses (FIG. 9 left hand side) and using a plaster with individual lenses (FIG. 9 right hand side) and the measured and calculated beam profile for a plaster with individual lenses (FIG. 10) according to an embodiment of the present invention.

FIG. 11 and FIG. 12 illustrate two examples of plasters comprising a gradient refractive index material according to embodiments of the present invention.

FIG. 13 illustrates a plaster comprising a liquid crystal gradient refractive index material according to an embodiment of the present invention.

FIG. 14 and FIG. 15 illustrate two examples of plasters comprising a reflective coating according to an embodiment of the present invention.

FIG. 16 illustrates a plaster comprising a homogenizer with double reflective surface according to an embodiment of the present invention.

FIG. 17 illustrates a plaster comprising phosphor material according to an embodiment of the present invention.

FIG. 18 illustrates a plaster comprising wedges for locally receiving side-lit radiation, according to an embodiment of the present invention.

FIGS. 19 to 22 illustrate examples of a plaster wherein phosphor material is used for emitting the therapeutic radiation, according to embodiments of the present invention.

FIG. 23 illustrates a system for radiating skin comprising a radiation device according to an embodiment of the present invention.

FIG. 24 illustrates an example of a plaster combining different optical elements for homogenizing the irradiation, according to an embodiment of the present invention.

The drawings are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn to scale for illustrative purposes.

Any reference signs in the claims shall not be construed as limiting the scope. In the different drawings, the same reference signs refer to the same or analogous elements.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Where in embodiments according to the present invention reference is made to a plaster, reference is made to a bandage or patch or medical dressing to be applied to a skin for treatment. The plaster therefore typically may be wearable. The plaster may be flexible such that it substantially follows the curvature of the skin, although embodiments of the present invention are not limited thereto.

According to a first aspect, the present invention relates to a plaster for providing radiation to the skin, being the area of interest. The plaster 100 may be adapted for receiving radiation from at least one radiation source, e.g. a plurality of radiation sources, positioned so that at least one of their projections perpendicular to an outcoupling surface 130 of the plaster falls or lies within the outcoupling surface 130. The position of the at least one radiation source therefore may be distributed over the plaster, excluding conventional side lit radiation, and including direct lit radiation or semi-direct lit radiation. In direct lit radiation, the radiation is directly emitted towards the outcoupling surface and is directly coupled out at the outcoupling surface. This may include radiation that is at least partly directly emitted in the direction perpendicular to the plane of the outcoupling surface. Semi-direct lit radiation refers to radiation that initially is not towards the outcoupling surface or where at least part of the radiation is initially not towards the outcoupling surface, but whereby on average the radiation travels at least 25%, e.g. at least 50%, e.g. at least 75% of its travel distance in the plaster towards the outcoupling surface and is directly coupled out at the outcoupling surface. The radiation may be received via a radiation receiving surface 110. The plaster comprises a homogenizer 120 for spreading of thus received radiation so as to homogenize the received radiation and a radiation outcoupling surface 130 for coupling out radiation to the skin, as illustrated schematically in FIG. 1. The plaster 100, or part thereof, may be made of a soft or flexible material, allowing good contact with the skin and making application and/or wearing of the device more pleasant for the user. The plaster 100 may be made in any suitable manner, such as for example by injection moulding, casting, cutting etc. The plaster 100, or a large part may be made of a material that is substantially transparent at wavelengths at which the plaster 100 may be used, e.g. in the ultra violet (UV) range. Some materials that could be used are silicone (PDMS) or epoxy, being examples of flexible materials, or COC, COP, PC, PMMA being examples of hard materials. For Polydimethylsiloxaan (PDMS), a transmission spectrum in the UV, visible light and near-infrared wavelength range is illustrated in FIG. 2. The wavelength or wavelength range of the radiation used may depend on the application. The plaster may for example be used for wound healing, in particular surgical wounds, for treatment of ulcers such as leg ulcers, diabetic ulcers or decubitus ulcers. The plaster or larger system also may be adapted for combining different applications. Other examples of applications may be the treatment of wrinkles, possibly in combination with an anti-wrinkle creme, disinfectioning of wounds, whereby UV radiation with a wavelength around 360nm or blue light with a wavelength around 430nm typically may be used, local treatment of Acne, whereby blue light in the wavelength range 400nm to 440nm may be used, treatment of Psoriasis or Vitiligo, whereby advantageously UV radiation with a wavelength of or around 31 lnm is used, skin cancer, Lupus where advantageously radiation with a wavelength of around 365nm is used, pain relief where advantageously blue and/or infrared radiation is used, etc. The plaster may be adapted for using different wavelengths using a type of radiation sources emitting radiation at different wavelengths or in different wavelength regions, using different types of radiation sources, each type emitting at different

wavelengths or in different wavelength regions, etc. It thereby is an advantage of

embodiments according to the present invention that spreading of the radiation of different wavelengths or in different wavelength regions can be obtained using one or more homogenizers according to embodiments of the present invention. As will be described further, the at least one radiation source may be embedded or unembedded. It is an advantage of embodiments wherein the radiation sources are not embedded that exchanging of radiation sources can be more easily performed.

According to embodiments of the present invention, the plaster 100 is adapted for receiving radiation from at least one radiation source positioned so that at least one of their projections perpendicular to the outcoupling surface falls within said outcoupling surface. The latter includes a top-lit radiation therapy system, although embodiments of the present invention are not limited thereto. The plaster 100 thus in some embodiments may be adapted for direct lit radiation. The plaster 100 may be adapted in shape for operating with direct lit radiation by providing particular radiation receiving surfaces, although the invention is not limited thereto. The plaster 100 also may be adapted for comprising radiation sources within the plaster. An advantage of such radiation setup is that the radiation needs to travel less distance in the plaster, compared to side lit systems, so that absorption is less of an issue. The use of such radiation setup also results in the skin being more directly radiated by the radiation sources 150 than e.g. in side lit radiation. In this way, a system with high efficiency and homogeneity can be achieved.

In some embodiments semi-direct lit radiation is performed, whereby the radiation or part thereof travels during at least part of the time that it is present in the plaster, not in a direction towards the outcoupling surface. The latter may be obtained, e.g. when a reflective surface is used and whereby the radiation is emitted or redirected in a direction opposite to the outcoupling surface, or whereby radiation travels over a short distance in a direction parallel to the outcoupling surface. In another embodiment, radiation first may be directed to a backside of the plaster where it then can be reflected to the light outcoupling surface. These embodiments typically may suffer from absorption problems (e.g. in UV applications) as the travelling distance in the plaster is increased. These embodiments may for example be used for converted radiation.

The plaster 100 may be adapted for receiving radiation from at least one radiation source 150, in some embodiments being a plurality of radiation sources. The at least one radiation source 150 may be part of the plaster 100, or may not be part of the plaster 100 but being an external component detachably or non-detachably connectable to the plaster 100. The plaster 100 may be provided with at least one recess 140 (shown in FIG. 1) such that the at least one radiation source 150 may fit or be inserted in the recess 140, although the invention is not limited thereto. Alternatively or in addition thereto, the recess 140 may be used for inducing an air gap between the plaster 100 and the radiation source 150. The radiation source 150 therefore may be not or only partially fitted in the recess 140 or be positioned adjacent thereto. The latter is described in more detail in a particular embodiment below. As indicated, the plaster 100 furthermore comprises a homogenizer 120 for spreading the radiation so as to homogenize the received radiation. Such homogenizer 120, which also may be referred to as homogenizing means, can be established in a plurality of ways. It may be an optical element adapted for spreading radiation. Such spreading may include any or a combination of directing, refracting, reflecting, scattering, converting, etc. The homogenizer 120 allows achieving a more homogeneous radiation distribution on the skin, compared to absence of a homogenizer. Different embodiments of the plaster 100 will be described, several of them illustrate different embodiments of the homogenizer 120. After the spreading of the radiation, the radiation also is coupled out. The plaster 100 therefore comprises an outcoupling surface 130 adapted to couple out the spreaded radiation. The outcoupling surface 130 may be or may comprise an outcoupling window. At least this outcoupling window fulfills the transparency requirements as described above. According to some embodiments, the plaster 100 may consist of one, two or more parts. In some particular examples, the device may consist of two parts, one for receiving the radiation, the other one for covering the area of interest, i.e. the skin. The second part, which may be referred to as the covering part, thus may be adapted for being in contact with the skin, when the device is in use. The covering part may be or may comprise the radiation outcoupling surface 130. The homogenizer 120 or homogenizing means, e.g. homogenizing optical element, may be part of the first part or the second part. In some particular examples, the covering part comprising the homogenizer 120 may be a set of lenses or may be a part having the same or different refractive index than the lens material. The covering part may for example be a third part, being on one side in contact with a second part being or comprising the homogenizer or the homogenizing means and on the other side in contact with or adjacent to the skin, when the device is in use.

By way of illustration, the present invention not being limited thereto, a number of particular embodiments are described in more detail below.

In one set of particular embodiments, the present invention encompasses a plaster 100 for providing radiation to skin, wherein the homogenizer 120 comprises at least one optical element inducing refraction, such that the incident radiation is coupled out substantially more homogeneously. The optical element in these cases therefore may be referred to as a refractive element. An advantage of such embodiments is that direct lit radiation can be performed without the need for further radiation guides where absorption often reduces the obtainable therapeutic effect.

In a first particular embodiment, the plaster 100 comprises a homogenizer 120 comprising a set of lenses. The lenses in the present example are adapted to act as hollow air- gap lenses. The plaster 100 therefore is adapted such that around the at least one radiation source 150, an air gap 122 is induced and the radiation receiving surface 110 of the plaster 100 is adapted in shape for refracting the incoming radiation. The shape of the radiation receiving surface 110 is adapted so that substantially all radiation stemming from the at least one radiation source 150 and coupled in to the plaster is refracted to the outcoupling surface 130 of the plaster 100. An example of such a plaster 100 is shown in FIG. 3. An efficiency (radiation coupled out of the plaster to the skin relative to radiation generated by the radiation source) on the skin of up to 80% can be reached. In some embodiments, the plaster may be adapted in thickness to optimize homogeneity of the radiation output while maintaining a compact device. The thickness of the plaster 100 may for example be about the distance between two radiation sources 150, as this assists in having a radiation distribution of a Lambertian emitter to be substantially homogeneous. According to some embodiments, aspheric lenses may be advantageously used resulting in a radiation distribution being either even more homogeneous or resulting in a radiation distribution having the same homogeneity for a smaller plaster thickness and high efficiency, i.e. 80% or higher. In one example, the plaster may have a particularly shaped radiation receiving surface 110. The radiation source 150 also is shown. The radiation source 150 may be placed adjacent to the recess, but not in contact with the radiation receiving surface 110, in order to maintain the presence of the air gap, allowing to achieve good homogeneity with a relatively thin plaster. Alternatively the radiation sources may be placed so that an air gap is present between the receiving surface of the plaster and the radiation sources, but the receiving surface is not lens or recess shaped, resulting in an efficiency that is higher than achieved with some embedded sources without air gap. The efficiency with embedded sources typically is material and wavelength dependent. For low absorbing materials, a major part of the radiation gets a chance to be coupled out and therefore contributes to a better homogeneity. For high absorbing materials, radiation at large emission angles can contribute to the homogeneity in case of an air gap rather than in case no air gap is present. The plaster 100 of the example of the present embodiment is made by injection moulding, although other manufacturing techniques also may be used.

It is to be noticed that, in each embodiment of the present invention, the plasters 100 preferably are used with radiation sources 150 having a Lambertian or Gaussian emission distribution with wide angle, as this assists in making the distribution more homogeneously. If the angle distribution of the emission pattern of the radiation sources is small, e.g. 60° or smaller, it is more difficult to make the distribution homogeneous on the skin. Typically the thickness of the plaster 100 may be increased then to obtain a more homogeneous distribution, being disadvantageous for compactness and consequently user comfort.

In a second particular example wherein the homogenizer 120 is based on at least one refractive element, refraction is provided by the plaster 100 comprising a set of separate lenses 300 rather than a single refractive surface. The separate lenses 300 have two refractive surfaces 302, 304, to allow more accurately refracting the radiation compared to a single refractive surface. Consequently, plasters according to the present example result in better spreading of the received radiation on the individual lenses 300 and thus resulting in good homogeneity of the radiation on the area of interest being the skin. This advantage can even be obtained for solutions wherein the distance to the skin is substantially smaller than the pitch between different radiation sources 150. An example of an individual lens 300 that may be used is shown in FIG. 4. The lens 300, which is in contact with the radiation source 150, e.g. by making it as an over moulded lens, may allow outcoupling of the radiation in a more appropriate direction, thus to allow assisting in the therapy. A further preferred example of an individual lens that may be used is shown in FIG. 5, illustrating an individual lens providing an air gap and two refractive surfaces. The individual lens has an a- spherical incoupling surface 302, also referred to as entrance surface, and a- spherical outcoupling surface 304, also referred to as exit surface. The exit surfaces of the individual lenses may operate as outcoupling surface 130 of the plaster 100. An example of a plaster 100 solution with separate individual lenses 300 is shown in FIG. 6. The individual lenses 300 again may be adapted in shape, e.g. have an a-spherical shaped. The individual lenses 300 may be centered on positions where radiation sources will be placed in the radiation therapy system. The separate lenses 300 may be flexible lenses, although embodiments of the invention are not limited thereto. The separate lenses 300 may be made for example of silicone, glass, plastics, polymers, a combination of glass and silicone, a combination of plastic and silicone, although embodiments of the invention are not limited thereto. The lens material or materials used may be substantially transparent for the typical wavelength range of the radiation with which the plaster 100 is intended to be used. As described above, the latter may be application specific. Individual lenses may be preferred over a layer, as typically the absorption and thus loss of radiation may be smaller with lenses, while obtaining good homogeneity at small plaster thicknesses.

In one example, the optical element(s) may be adapted for causing a peak in the refracted radiation at 45°. The intensity of the emission is around one third of the peak intensity. In some examples, the distance of the radiation sources to the skin may be about 5 mm, and the lens center thickness may be about 2 mm. The proposed lenses may

advantageously be made of material showing low absorption. The lenses may have a smooth front side for application on the skin or a soft (silicone) sheet of about 0.4 mm between hard lenses and skin may be provided.

In order to fixate the distance between the radiation sources 150 and the skin, the distance between lenses 300 or radiation sources 150 and the skin can optionally be fixated using spacers 320. Such spacers 320 may be made of any suitable material, such as for example from a plastic material. The spacers 320 can be in particular places and not among all the radiation sources 150. Spacers 320 and lenses 300 can be made with the same mould, resulting in a more easy manufacturing technique of the plaster 100. In preferred embodiments, the spacers may be omitted and a spacing function between radiation sources and skin may be performed by the optical elements, e.g. lenses. In some embodiments, furthermore a thin contact sheet, e.g. a silicone sheet, is provided on top of the lenses such that it is positioned between the lenses and the skin, when in use. The thin sheet does not or not substantially influence the radiation distribution but it increases the comfort for wearing by providing a softer feeling on the skin, compared to the feeling induced by the lenses when these would not be covered. FIG. 7 and FIG. 8 illustrate a calculation of the radiation distribution on the skin for a plurality of radiation sources 150 and the radiation distribution for one radiation source 150 thereof respectively for a plaster 100 without lenses 300 (left hand side) and for a plaster 100 with individual lenses 300 (right hand side). It can be derived that the homogeneity improves from about 50% to about 90%> when using individual lenses 300. Comparison between plasters wherein a larger distance to the skin is provided and plasters with a lens homogenizer shows that a good homogeneity as well as the combination of good power density and good radiation homogeneity is only obtainable with a lens homogenizer and not by increasing the distance between the radiation sources and the skin for plasters not having a lens homogenizer. The remaining steep peaks and dips in the design with the lens will be less pronounced or disappear when tolerance of position of the sources and the lenses is taken into account (what is shown is a calculation at nominal position).

FIG. 9 illustrates the radiation pattern (polar plot) of the radiation for a plaster 100 without lenses (left hand side) and a plaster with individual lenses 300 (right hand side).. It can be seen that the effect of using individual lenses 300 is a decrease in the radiation intensity in the centre, i.e. corresponding with substantial perpendicular incidence on the outcoupling surface for direct lit radiation. In the particular example of a 10 mm pitch for the radiation sources and a 5mm distance to the skin, the intensity in the central position is reduced to about 30% of the peak intensity reached as can be seen from the arrows in FIG. 9 (right hand side), and the intensity peak position has shifted from a central position at 180° (or equivalent therewith 0°) to an angled position at about 135° (or equivalent therewith 45°). The intensity distribution in longitudinal direction 352 and in lateral direction 354 is shown for the situation without lenses (left hand side) and for a plaster with separate lenses (right hand side). As shown in FIG. 7 and FIG. 8, the altered radiation pattern gives rise to an overall more homogeneous radiation distribution on the skin. The measured and calculated beam profile using an individual lens is shown in FIG. 10, whereby the curve 362 illustrates the measured beam profile while the curve 364 illustrates the calculated beam profile. In a third particular example, refraction is obtained in a plaster that is at least partially made from gradient index material 370, providing a gradient refractive index in the plaster 100. Such gradient index material 370 may for example be a multilayer stack comprising layers of different refractive index material or a single, gradually doped, material inducing a gradient, e.g. monotone gradient, refractive index. The refractive index may vary from a high refractive index at the bottom of the plaster where the radiation receiving surface or incoupling surface 110 is to a lower refractive index at the top of the plaster where the outcoupling surface 130 for the radiation is positioned. The incident radiation rays then are bent from the direction of the radiation source 150, at the bottom of FIG. 11, towards the outcoupling surface 130.

It is an advantage of such a combination that the plaster 100 can be reduced to a very small thickness because the radiation rays can be bent over a short distance, resulting in an increased user comfort. Further, providing the radiation sources 150 in recesses 140 results in a reduced loss of radation (Fresnell losses) at the incoupling surface of the plaster, because more radiation will enter the plaster 100. An example thereof is shown in FIG. 12.

Whereas in the third and fourth particular example, the refractive index gradient of the material was fixed for a certain wavelength of radiation by using gradient refractive index material 370, a variable gradient refractive index material also could be used in such embodiments, by including a liquid crystal material 380 for inducing a gradient refractive index. Such a liquid crystal material 380 may have a tunable refractive index gradient. A possible setup for such a plaster is shown in FIG. 13. In the example shown in FIG. 13, the liquid crystal material 380 is embedded between flexible substrates 390, in the present case having the same refractive index, although the invention is not limited thereto. An electrical conductivity layer (not shown) is provided on one of the flexible substrates for tuning the refractive index. Such layer may preferably be a transparent conductive layer, e.g. a tin oxide or indium tin oxide. At the opposite side of the liquid crystal material, a second electrode may be provided (not shown). Such electrode also may be a transparent electrode. The liquid crystal material may be embedded in the solid flexible substrate 390 as shown in FIG. 13 but may also be embedded in the plaster using other means. The substrate 390 as well as the liquid crystal material advantageously is transparent for the radiation used.

Whereas a number of homogenizers 120 based on refractive elements have been described, the present invention is not limited thereto and other types of refractive elements as known by the person skilled in the art also are encompassed within the present invention. In some embodiments according to the present invention, the homogenizer 120 may comprise one or more reflective components, whereby the reflective components provide spreading of the radiation.

In one particular embodiment, the homogenizer 120 comprises a reflective layer or reflective coating 400. Such a reflective layer or coating 400 may be a metallic layer, a dielectric reflective coating such as for example a reflective dielectric multilayer.

According to the present example, radiation of the radiation sources 150 is first directed to the reflective layer or coating 400 positioned opposite to the outcoupling surface 130 and then redirected by reflection at the reflective layer or coating 400 to the outcoupling surface 130. In this way an enlarged optical path is provided (compared to direct emission to the outcoupling surface 130) for at least part of the radiation, allowing for more mixing and consequently for a more uniform radiation distribution. The radiation sources 150 may for example optionally be embedded in the plaster material, such as e.g. LEDs that may be embedded in the plaster 100. Electrical connectivity can advantageously be provided through transparent conductive layers 410, although small conventional metallic conductors also could be used. The radiation sources 150 according to the example of the present

embodiment are oriented for substantially emitting in the direction opposite to the

outcoupling surface 130 and therefore direct their radiation towards the reflective coating 400. The reflective layer or coating 400 then redirects the radiation towards the outcoupling surface 130. An example of such embodiment is shown in FIG. 14, embodiments of the present invention not being limited thereby. The distance between the radiation sources 150 and the outcoupling surface 130 may be optimized such that the radiation sources 150 do not leave a shadow on the skin, and thus homogeneous irradiation is obtained. Alternatively, the sources may be placed closer to the outcoupling surface 130, e.g. even directly in contact with the outcoupling surface. In one particular embodiment, the reflective coating 400 may have a predetermined shape, e.g. a curved shape and/or periodical structure, in a similar way as described for the lenses. The reflective coating 400 may for example be shaped such that for each radiation source 150, the reflective coating 400 near the radiation source 150 acts as a mirror, e.g. an aspherical mirror such as e.g. an elliptical or parabolic mirror, or a spherical mirror. An example thereof is illustrated in FIG. 15, illustrating such an embodiment wherein even better controlled spreading of the radiation is obtained. Again in this example, the distance from the radiation sources to the reflective surface and the distance to the skin (thickness of plaster) can be optimized. Whereas a number of homogenizers 120 have been described based on different reflective materials, the invention is not limited to the embodiments described in detail and encompasses the use of other reflective materials known to the person skilled in the art. For example, in one particular embodiment, the radiation source 150 is embedded in the plaster and emits its radiation in the direction of the outcoupling surface. The radiation is spread using a set of two reflecting mirrors 452, 454, as e.g. shown in FIG. 16. The first mirror 452 may be partially reflecting, so as to allow some radiation to pass through the first mirror 452 directly and some other portion to be spread using a double reflection. The latter is especially suitable for high power radiation sources 150. Whereas embodiments are described whereby the radiation sources are embedded in material positioned between the reflecting mirrors, similar embodiments wherein the sources are not embedded in material but wherein the sources are positioned in air between the reflecting mirrors or embodiments where a combination of air and material is present are also envisaged with embodiments of the present invention. It is an advantage of embedded radiation sources that the radiation sources are fixed in the plaster, avoiding the need for alignment. It is an advantage of non-embedded light sources that they are easily replaceable.

In some embodiments of the present invention, the homogenizer 120 may comprise a scattering element for scattering the radiation emitted by the radiation sources 150. The scattering element may be formed by adding optically scattering particles to the material constituting the plaster. Alternatively or in addition thereto, the scattering element also may be a separate layer or portion of the plaster having optically scattering properties.

In some embodiments of the present invention, the homogenizer comprises at least one radiation converting element for converting radiation from one wavelength into radiation of another wavelength. Such a converter may be a phosphor layer for conversion of radiation. As such materials typically emit in all directions and can be spread across the plaster, such converting elements allow increasing the homogeneity of the irradiation obtained through a plaster. Such embodiments can also be considered as semi-direct lit, whereby the excitation radiation is converted in therapeutic radiation and whereby on average the combination of excitation radiation and therapeutic radiation emit at least 25%, e.g. at least 50% or e.g. at least 75% of the travel distance in the plaster in the direction of the outcoupling surface and is coupled out directly at the outcoupling surface.

In one particular example, the radiation converter element 500 is established by adding phosphor particles 502 to the plaster material, such that the phosphor is present throughout the plaster 100. When for example UV LEDs are used, a phosphor material converting the UV radiation (full line arrows) into for example red light (dashed line arrows) can be beneficial, in that for example in wound healing applications the red light may accelerate and enhance the wound healing process. The phosphor converts the initial radiation (full line arrows) from the radiation sources 150 completely or partly in converted radiation (dashed line arrows). If partly conversion is performed, this means that the system radiates at two or more different wavelengths or in two or more different wavelength ranges. The phosphor particles may also induce a scattering effect on the original radiation, such that the phosphor also contributes to obtaining a more homogeneous radiation distribution on the skin for the original radiation. In order to recuperate converted radiation emitted towards the radiation receiving surface 110 of the plaster 100, a reflective dichroic layer or coating 510, may be present adapted for reflecting the converted radiation, while allowing radiation from the radiation sources 150 to pass through into the plaster 100. An example of a plaster 100 with phosphor particles 502 in the plaster material is shown in FIG. 17 illustrating conversion of an incident radiation ray and emission of converted radiation in different directions.

Recuperation of converted radiation emitted initially in a wrong direction using a dichroic layer 510 is also shown. Down conversion, e.g. from UV radiation to blue radiation, is the most efficient method to convert radiation, however, infrared or red light can be used in combination with nano-particles that convert the (infra)red light into lower wavelengths such as blue light). This latter is called up conversion. As up conversion typically may be less efficient, this may be less preferable in some embodiments. Besides increase of homogeneity, adding a phosphor thus also provides the advantage of creating a combination of radiation of different wavelengths, while only one type of radiation source 150 is required.

In some examples, the phosphor material may be incorporated in a smaller part of the plaster, e.g. as a smaller layer thereof. The phosphor material also may be present in a liquid being part of the plaster, in a gradient reflective index material being part of the plaster, on a flexible substrate part of the plaster, advantageously on the side of the radiation sources, etc.

In one set of particular embodiments, the plaster comprises a liquid material, transparent for the radiation. The plaster may comprise a solid flexible material enclosing the liquid material. The liquid material may have a thickness, sufficiently large to have a homogeneous light distribution. The use of a liquid material may allow using the liquid simultaneously as a cooler. The application of liquid material furthermore may result in a cheaper system and a softer system resulting in a good wearability comfort. Alternatively, the combination of solid and liquid material could be combined with a phosphor material as described above to increase homogeneity. For example, a hard lens material can be combined with a liquid material to have a soft cover on top of the hard lenses. The liquid material can have another refractive index than the lens material and the lens shape may be optimized and adapted for the refractive index of the liquid material.

In another set of embodiments the plaster is adapted to receive radiation from a plurality of radiation sources, spread across the back surface of the plaster. The plaster may be adapted for receiving radiation in a direction substantially parallel to the outcoupling surface and comprises a homogenizer wherein a plurality of 2-dimensional wedges are present in order to allow incoupling of radiation in a direction substantially parallel to the outcoupling surface and locally redirect the radiation in a direction substantially

perpendicular to the outcoupling surface. An example thereof is shown in FIG. 18, illustrating radiation incoupling in a side-ways direction, i.e. parallel to the outcoupling surface, spread over a plurality of wedges 550 distributed over the backside of the plaster 100. The latter has the advantage over conventional side lit systems, that the distance to be travelled by the radiation in the plaster can be substantially smaller. These embodiments also can be considered semi-direct lit radiation embodiments.

By way of further illustration, some more examples are shown with reference to FIG. 19 to 23. The examples show embodiments of a plaster using radiation sources emitting excitation radiation for exciting phosphors emitting the therapeutic radiation used for therapy. In FIG. 19, the plaster comprises a plurality of radiation sources 150 positioned and embedded in the plaster in a first layer comprising phosphor material. The plaster furthermore comprises a second layer comprising the outcoupling surface, and a dichroic refiection layer, separating the first layer and the second layer. The radiation sources emit excitation radiation for exciting phosphor material in a first layer of the plaster. In the present example, the radiation sources are positioned embedded in the plaster close to the dichroic refiection layer. Excitation radiation is on one side of the first layer reflected by the dichroic refiection layer, which is adapted to reflect the excitation radiation and not the therapeutic radiation, and on the other side of the first layer reflected by a reflective element, so that the excitation radiation is captured in the first layer. The excitation radiation can, before or after refiection, excite phosphor material so that the phosphor material emits therapeutic radiation used for the therapy. This therapeutic radiation is coupled through the dichroic reflective layer to the second layer and may be coupled out through the outcoupling surface. In a similar example shown in FIG. 20, the radiation sources 150 are positioned at another position in the first layer or adjacent thereto, resulting in a similar operation. In two other examples, the second layer comprises the phosphor material and the first and second layer is separated by a different dichroic reflective layer, transmitting the excitation radiation but reflecting the therapeutic radiation. Excitation radiation generated in radiation sources in the first layer then is transmitted through the dichroic reflective layer in the second layer, where it excites phosphor material. The therapeutic radiation of the phosphor material typically may be emitting therapeutic radiation in all directions, some being coupled out through the outcoupling surface directly, and some being coupled out after redirection by the dichroic reflective layer. Examples thereof are shown in FIG. 21 and FIG. 22 indicating such embodiments for different positions of the radiation sources in the first layer.

In a further aspect, the present invention relates to a system 700 for radiation treatment of the skin, being the area of interest, wherein the system 700 comprises a plaster 100 as described in any of the embodiments described above and furthermore comprises at least one radiation source 150 for generating radiation. Such at least one radiation source 150 may be a plurality of radiation sources 150. In the system setup 700 the radiation sources are positioned so that at least one of the projections of the radiation sources in a direction perpendicular to an outcoupling surface of the plaster lies within the outcoupling surface. Such a system allows for example for direct lit radiation, resulting in a compact and highly efficient system 700. The part comprising the radiation sources 150 and the plaster 100 may be detachable from each other. The system 700 furthermore may comprise an energy source 710 for powering the at least one radiation source 150. Such an energy source 710 may for example be a battery, a solar cell, etc. although the invention is not limited thereto.

Alternatively or in addition thereto, the at least one radiation source 150 also may be powered by an external energy source. The at least one radiation source 150 may be connected to the energy source by electrical connections 720. The system 700 furthermore may comprise a controller 730 for controlling the powering of the radiation sources, e.g. for controlling the radiation intensity and radiation time. Such a controller 730 may be provided in hardware as well as in software, and may be implemented as a microcontroller or microprocessor. By way of illustration, the present invention not being limited thereby, an example of a system 700 for radiation treatment of skin is shown in FIG. 23, indicating a plaster device 100, radiation sources 150, electrical connectors 720, a controller 730 and an energy source 710. It will be clear to the skilled person that other components, typically present in conventional systems for radiation therapy, also may be included.

The foregoing description details certain embodiments of the invention. It will be appreciated, however, that no matter how detailed the foregoing appears in text, the invention may be practiced in many ways, and is therefore not limited to the embodiments disclosed. It should be noted that the use of particular terminology when describing certain features or aspects of the invention should not be taken to imply that the terminology is being re-defined herein, to be restricted or to include any specific characteristics of the features or aspects of the invention with which that terminology is associated.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments.

Another example is a plaster 100, wherein at the top portion, near the outcoupling surface 130, a phosphor material 502 is provided, e.g. as a layer or coating 500. Optionally a dichroic layer 510 may be provided at the bottom of the phosphor layer 500. As the excitation radiation from the radiation sources 150 is homogeneous near the outcoupling surface 130, the converted radiation also will be homogeneous. An example of such a plaster 100 is shown in FIG. 24, illustrating a combination of the use of a gradient index material 380 and a phosphor conversion element 500 combined in one optical element.

Advantages of not embedding the light source(s) in the plaster generally are the protection of fragile LEDs or LEDs dome from damage during the embedding process and the ability to exchange light source(s) (e.g. with a different wavelength light source or to replace a defective light source). Advantages of embedding the light source(s) in the plaster generally are a higher efficiency because no extra interfaces are used and a better alignment of the light source(s) with the optical element(s) of the plaster.

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. For example, embodiments of the present invention also encompass a method for providing radiation to skin, the method comprising providing radiation to a plaster from at least one radiation source positioned such that the projection of the at least one radiation source in a direction perpendicular to the outcoupling surface lies within the outcoupling surface, homogenizing the thus received radiation in the plaster (100), and coupling out the radiation from the plaster (100) to the skin.

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. Any reference signs in the claims should not be construed as limiting the scope.