WO2012011042A2 - Improvements in phototherapy - Google Patents

Abstract

An apparatus (27) for bio-stimulating phototherapy is provided herewith. The apparatus comprises a light source (29) for providing light with a phototherapeutic wavelength and a controller (37). The controller is configured to control operation of the apparatus, in particular the light source. The apparatus is configured for illuminating the skin (3) of a subject's body portion (1) with light emitted by the light source. The controller is configured to control the wavelength of at least a portion of the light as a function of at least one of melanin index (M) or the lightness (L*) of the skin. A method is also provided.

Description

Improvements in phototherapy

TECHNICAL FIELD OF THE INVENTION

The present disclosure relates to phototherapy, in particular to apparatus and methods for dermatological phototherapy. The apparatus and methods may be used both in professional and domestic use, and for curative, cosmetic and wellness purposes.

BACKGROUND OF THE INVENTION

Phototherapy, treating a patient with light, is known for treatment of various conditions. It has been found that optical absorption of the skin may affect treatment efficiency. Both ultraviolet (UV) and/or infrared (IR) treatments have proven to be able to cause damage to the skin when the radiation absorbed by the skin exceeds a threshold.

UV treatment is often used in treatment of various dermatological diseases such as e.g. psoriasis. The main problem of UV treatment is that the absorbed UV radiation can cause DNA damage and skin cancer when the irradiation dose is too high. Often a MED value (minimum erythemal dose) is used as a guide to determine a safe UV dose. The MED is the smallest dose to produce visible reddening of the skin, which is indicative of a skin irritation. The MED is known to vary with skin type. For characterizing skin type, the Fitzpatrick scale is commonly used. However, large differences in MED are found between different individuals of the same Fitzpatrick type, requiring determination of the MED by applying different amounts of light to the skin and observing at what dose erythema has occurred. This method inherently imposes irritation and potential damage to the tested skin portion.

Infrared (IR) phototherapy is often used in the context of hair removal (depilation), where a sufficient amount of heat energy is needed near the hair shaft and hair bulb to 'burn' the hair. Such treatment should be performed without damaging the skin through energy absorption. The correct amount of energy deposition is generally determined by trial and error.

A presently increasingly relevant field - and being the field of the present disclosure - is that of bio-stimulation of living tissue. Bio-stimulating skin phototherapy may be applied for treating jaundice and psoriasis and may comprise curative phototherapy like wound healing or cosmetic phototherapy like rejuvenation. A particular branch of bio- stimulating phototherapy is known as Low Level Light Therapy (or: LLLT). In the field of bio-stimulation of living tissue, any damage to the tissue must be prevented. This poses significantly stricter requirements on the applied dose, since doses that for example are considered acceptable for hair removal may in fact already exceed stimulatory effective thresholds. However, reducing the applied illumination doses for safety reasons can easily lead to administration of a dose that is therapeutically ineffective. Successful treatment may thus require individual adjustment of dose and protocol. The MED indicates an upper dose limit but provides no useful information for doses below the MED. Indeed, for bio- stimulatory treatments clinical test results based on MED or the Fitzpatrick scale have proven inconclusive.

US 2008/269849 discloses an apparatus for delivering phototherapy which includes at least one substrate, at least one emitter mounted on the substrate, and which emits at least two peak wavelengths of light, and an electronic circuit that controls emitter timing. The apparatus is configured as a dressing. A corresponding method includes delivering a first pulse of light to the target tissue from the emitter with a peak wavelength of light, and delivering at least a second pulse of light having a peak wavelength of light that is different from the peak wavelength of the first pulse of light, and the steps define a method of delivering a series of pulse sets of light, and the first and second pulses of light define a pulse set of light. Also disclosed are modular phototherapy units, control of timing of phototherapy by a perfusion detector, and use of long wavelength light for hyperbilirubinemia.

However, also in the latter case no accurate determination for proper dosage is provided.

Consequently, there is a desire for equipment and methods for providing both safe and effective bio-stimulation phototherapy, in particular for domestic use.

SUMMARY OF THE INVENTION

An apparatus for bio-stimulating phototherapy is provided herewith.

The apparatus comprises a light source for providing light with a phototherapeutic wavelength and a controller. The controller is configured to control operation of the apparatus, in particular the light source. The apparatus is configured for illuminating the skin of a subject's body portion with light emitted by the light source. The controller is configured to control the wavelength of at least a portion of the light, advantageously substantially all the light, as a function of at least one of the melanin index (M) and the lightness (L*) of the skin.

Phototherapy is inherently wavelength sensitive and its effectiveness depends on the net overlap of source emission, melanin filter transmission and therapeutic absorbance. A maximal effectiveness at a given external irradiance is desired because the irradiance level and side effects can then be kept to minimum.

Melanin absorbs radiation, hindering attaining an intended treatment dose in the body portion. The melanin absorption or filtering function is wavelength dependent. If the absorption by the melanin cannot be neglected (e.g. in case of a dark skin), the wavelength dependence of the melanin filter will be introduced in the function. Because the absorption is a decreasing function of the wavelength, the average wavelength of the emission must now be shifted to a higher value to maintain maximum effectiveness. The higher the melanin content in the skin, the larger the shift will be. The melanin index M indicates the melanin content in the skin considered and the lightness L* is defined in 1976 by the Commission International d'Eclairage (CIE) and is a measure of how the human eye perceives the lightness of the skin, see M.D. Shriver and E.J. Parra, "Comparison of Narrow-band reflectance spectroscopy and tristimulus colorimetry for measurements of skin and hair color in persons of different biological ancestry", Amer. J Phys Anthropology 112: 17-27 (2000). In humans melanin is almost exclusively located in the epidermis. It has been found that by determination of the melanin index or the lightness the irradiation losses in the epidermis may be correctly assessed, and that for deeper-lying tissue (e.g. dermis, hypodermic tissue) absorption losses due to melanin are of little to no influence. Hence, the actually administered phototherapeutic dose into these deeper-lying tissues can be reliably assessed. Determining the melanin index or the lightness of the skin portion provides quantitative information on, and determination of, the effective filtering function of the skin due to the melanin. The melanin index M may be measured by apparatus commonly used in cosmetic industry, e.g. the Skin Pigmentation Analyzer © SPA 99 of CK electronic GmbH, or the DSM II

ColorMeter by Cortex Technology, which latter apparatus can measure both the melanin index M and the lightness L*.

Measurement of the melanin index is preferred over measuring the lightness since it has been found that the melanin index is a more reliable parameter for quantifying the melanin content of the skin, see Shriver and Parra cited above.

Controlling the wavelength of at least a portion of the phototherapy light as a function of melanin index and/or the lightness of the skin thus allows to provide a predictable, or rather predetermined, irradiance and spectral energy density to the body portion below the epidermis, as well as a predictable, or rather predetermined, absorption by the melanin in the epidermis. By appropriate selection of the wavelength provided by the apparatus to the body portion, the administered wavelength and spectral energy distribution may be adapted to the phototherapeutic effective wavelength range or spectral absorption function of the tissue to be treated. This enables balancing between on the one hand optimization of therapeutic efficiency and on the other hand minimal heating and/or damage the epidermis due to absorption by the melanin.

Controlling the wavelength of the light may be effected in various ways, depending on the light source.

The melanin dependent function may comprise a wavelength and melanin- index dependent irradiance correction factor Icf = Icf(M, λ) = exp(Cm μ(λ) d), wherein Cm is a measure of the concentration of melanosomes in the epidermis of the skin portion which may be stated in terms of the melanin index M as Cm = (M-20)/150 and may be

approximated in terms of the lightness L* as Cm = 1.925 - 0.44 ln(L*), μ(λ) describes the wavelength dependent absorption of the melanin and may be approximated as μ(λ) = μο λ^"3'33 = 6.6 x 10¹¹ λ^"3'33 in units of cm^"1 with λ in units of nm and wherein μο is the average absorption coefficient of a single melanosome, and wherein d accounts for the optical path in the epidermis. The thickness of the epidermis generally varies between about 0.4 mm to about 1.2 mm, taking scattering into account d may be in a range from about 0.004 to about 0.024 cm, averaging over thickness variations and scattering provides a generally applicable range of about 0.008-0.016 cm, and a practical approximation is d = 0.012 cm. The function Icf corresponds to the inverse of the attenuation of the radiation by melanin absorption, and it provides an approximation of the modification function of the skin under consideration. The function is applicable to usefully provide correction factors over a large wavelength range, from UV to near IR wavelengths, and for substantially all skin types, ranging from light Caucasian type skin to dark Negroid type skin. The melanin concentration Cm can vary between 0.013 for white skin and 0.4 for Negroid skin. This dependence also implies a very strong filter effect towards shorter wavelengths in the blue part of the spectrum.

Advantageously, the melanin index is determined in a wavelength range between approx. 400 nm and approx. 2000 nm, in particular between approx. 500 nm and approx. 1500 nm, more in particular between approx. 600 nm and approx. 900 nm, and the body portion is illuminated with a phototherapy wavelength in that wavelength range. It has been found than in the wavelength range between ca. 400-2000 nm several phototherapeutic treatments may be provided. From ca 450 nm, absorption of light by haemoglobin and oxyhaemoglobin generally decays with increasing wavelength. A local maximum is located between ca 550-600 nm with a steep decrease for longer wavelengths. On the other hand, absorption by water generally increases from ca 450 nm to 2000 nm with a number of absorption peaks near particular wavelengths, in particular around ca 1600 nm. Melanin has a generally decreasing absorption over the wavelength range 400-2000 nm. Between ca 500-1500 nm absorption of (oxy)haemoglobin and water is reduced and in the wavelength range of ca 600-900 nm the main absorber is melanin. However, since the wavelength dependent absorption profile of melanin is known and rather smooth, correction may also be effectively employed in wavelength ranges where (oxy)haemoglobin and water have a significant absorption influence.

The light source may comprise one or more light emitting diodes (LEDs). LEDs may provide light in various well defined wavelengths (colors) at high efficiency and produce little heat compared to other light sources. The LEDs may therefore be placed close to the body portion. LEDs are generally well controllable with respect to output power and may be rapidly switched, enabling fine control over the operation of the apparatus. Moderate and high-power LEDs which do not exhibit superluminous or laser operation are particularly suited for use in bio stimulation since such LEDs do not exhibit a threshold-behavior in the emitted power and continuous power control is facilitated. A light source comprising plural LEDs facilitates a large effective surface area.

The wavelength emitted by LEDs may be controlled and modified by varying the current, voltage and/or the temperature of the LEDs. A LED may comprise plural LED units integrated in a single object which emit in different wavelengths, an RGB-LED

(comprising Red-, Green-, and Blue-emitting LEDs).

At least a portion of the apparatus may be formed to conform to at least part of the subject's body portion, e.g. by comprising a flexible, pliable or generally deformable portion such as a patch or bandage. The apparatus being formed for conforming to at least part of the body portion to be treated improves user comfort and allows prolonged treatment. Such apparatus, in particular in the form of a patch or bandage, may be worn inconspicuously under clothing. Such apparatus allows improved and predictable illumination of the body portion since shifted illumination portions and/or shadows caused by relative movement of the apparatus and the body portion are prevented. Further, illumination at an oblique angle may be prevented which may otherwise cause undesired reflection of the light and inaccurate dosing.

The apparatus may be configured for providing the light in a series of optical pulses with a controlled or controllable pulse repetition rate, with the pulses having a controlled or controllable pulse irradiance and/or pulse duration. The controller may be configured to control the pulse irradiance the pulse duration and the pulse repetition rate as a function of the melanin index or the lightness of the skin to provide an effective time averaged irradiance below a predetermined value. Due to the provision of the light in the form of optical pulses, the applied irradiance, the effective time averaged irradiance, and the total administered dose may efficiently be controlled substantially independently. The controller may be configured to control the pulse irradiance, the pulse duration and/or the pulse repetition rate as a function of time during operation of the light source, so that a time- varying effective time averaged irradiance may be provided, which may be controlled as a function of one or more skin parameters, e.g. melanin index, in particular in case of prolonged treatment with near-UV light which may cause skin tanning, or blood flow affecting thermal balance of the skin, dryness or sweating, affecting reflection of the skin.

The apparatus may comprise at least one sensor for non-invasively determining the melanin index of a subject's skin portion. Advantageously, the sensor is connected with the controller. Thus a compact integrated apparatus may be provided. Plural melanin index sensors may assist accounting for local melanin index variations, improving treatment efficiency and reducing accidental local overdosing.

The apparatus may comprise at least one further sensor for determining at least one further skin parameter. This allows additional control of and feedback on the treatment. An important parameter in phototherapy is the skin temperature. The further sensor may therefore suitably be a thermometer, e.g. a contact thermometer or an optical thermometer.

The apparatus may be configured for treating curative and cosmetic treatments. Examples are wound healing, pain, psoriasis and skin rejuvenation, which conditions may be treated in a professional setting and/or in a domestic environment.

The controller may be programmable. The apparatus may comprise one or more user interfaces for programming the controller. The apparatus may comprise one or more interfaces for providing a program in a machine readable format for programming the controller, e.g. a card slot, a wireless data link etc.

Further, in accordance with the above, an improved method of bio-stimulating phototherapy is provided herewith. The method comprises the steps of: determining a first wavelength range which is a bio-stimulating wavelength range for treatment of a subject's body portion;

determining at least one of the melanin index (M) and the lightness (L*) of the skin of the body portion; illuminating the body portion with light having a second wavelength range. The second wavelength range is modified from the determined bio-stimulating wavelength range by a predetermined amount, and the amount is determined as a function of the melanin index and/or the lightness.

The modification may comprise a frequency shift and/or a modified spectral width. The amount may be defined in units of percentages, wavelengths, (relative) spectral energy density etc.

The method may comprise the further steps of: determining a first irradiance for administering a treatment corresponding to the first wavelength; determining a second irradiance for administering a treatment corresponding to the second wavelength, wherein the second irradiance is determined as a function of the first irradiance, the second wavelength and the melanin index and/or the lightness; illuminating the skin of the body portion with the second wavelength at the second irradiance. Such method allows improving therapy accuracy by compensating a reduced spectral efficiency with an increased irradiance.

The method may also or alternatively comprise the further steps of:

determining a first phototherapy dose for administering a treatment corresponding to the first wavelength; determining a second phototherapy dose for administering a treatment corresponding to the second wavelength, wherein the second phototherapy dose is determined as a function of the first phototherapy dose, the second wavelength and the melanin index and/or the lightness; and providing the second phototherapy dose to the body portion by illuminating the skin of the body portion with the second wavelength. With such method, the administering of a desired effective dose and attaining of a desired effect is facilitated.

These and other aspects will hereafter be elucidated with reference to the figures of the drawings, which indicate examples for explanatory purposes only. Various other embodiments may be conceived within the scope of the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

Fig. 1 is a schematic representation of a skin portion;

Fig. 2 indicates typical irradiance correction factors for different skin types; Fig. 3 is a schematic representation of a spectral absorption profile and a spectral emission profile with partial overlap;

Fig. 4 indicates therapeutic effectiveness of a particular therapeutic illumination for different epidermal melanin concentrations Cm;

Fig. 5 indicates therapeutic effectiveness of therapeutic illumination with different spectral widths of the light source;

Fig. 6 indicates an effect of different spectral widths of the absorption function of the tissue to be treated;

Fig. 7 is a block scheme of an embodiment of a method of bio-stimulating phototherapy of a subject's body portion;

Fig. 8 is a schematic side view of a phototherapy apparatus;

Fig. 9 is a schematic side view of another phototherapy apparatus.

DETAILED DESCRIPTION OF EMBODIMENTS

It is noted that in the drawings, like features may be identified with like reference signs. It is further noted that the drawings are schematic, not necessarily to scale and that details that are not required for understanding the present invention may have been omitted. The terms "upward", "downward", "below", "above", and the like relate to the embodiments as oriented in the drawings. Further, elements that are at least substantially identical or that perform an at least substantially identical function are denoted by the same numeral.

Fig. 1 illustrates illumination of a human body portion 1, showing a skin portion 3, and illumination light 5. The skin 3 comprises an epidermis layer 7 of ca 0.1 mm thickness, a ca 1-4 mm thick dermis layer 9 covering hypodermic tissue 11. A fraction of the illumination light 5 penetrates into the dermis 9, and another fraction may penetrated into the hypodermic tissue 11 indicated with the arrows 13 and 15, respectively.

In the epidermis 7, the main optical absorbers are melanin and water. In the dermis 9, the main optical absorbers are water and blood. Hence, the absorbing or filtering effect of melanin is concentrated in the epidermis 7. It has now been found that once the reduction in optical energy by the epidermis 7 is known, the fraction of the energy available for deposition in the dermis 9 and hypodermic tissue 11 can be calculated. It has further been found that determining the melanin index of the skin portion 3 in fact returns the melanin index of the epidermis 7 and thus provides a reliable quantification of the filtering effect of the epidermis 7 and determination of the dose available for deeper-lying tissue. Similarly, the absorption of the illumination light 5 by the melanin can be readily determined and heating of the epidermis 5 can be predicted to prevent overheating or hurting.

The filtering effect of the melanin in the epidermis can be substantial. The resulting correction factor Icf for different skin types are indicated in Fig. 2: light Caucasian skin with M = 26 (full lines), Asian skin with M = 42.5 (dotted lines) and dark Negroid skin with M = 80 (dashed lines). From Fig. 2 it becomes clear that the irradiance dose to be applied onto the skin may be a large multiple of the dose to be deposited in the dermis or hypodermic tissue, in particular for phototherapy with blue light for Asian or Negroid skin types.

The dose is a combination of illumination irradiance and illumination time.

Adapting the irradiance and the dose to the local melanin index of the subject's skin will significantly affect and improve the effectiveness of the phototherapy. Also, safety of phototherapy is improved since irritation, damage and/or pain are substantially prevented. Phototherapy may therefore be made available for domestic use with little to no risk of damage or maltreatment.

Fig. 3 indicates a spectral absorbance profile Α(λ) of a particular skin condition and a spectral energy distribution of applied phototherapeutic light provided by the apparatus ί(λ). In a wavelength range where both spectra overlap (see hatched area), the treatment may be effective, depending on the amount of overlap and energy content in the range of overlap. Full overlap would be optimum for treatment, but this may lead to harming the skin, as set out above. With the apparatus and method provided herewith the effective overlap is balanced against (the risk of) undesired absorption by the melanin.

Fig. 4 shows the effect of melanin in the skin. Each frame shows three curves: one for white skin with an epidermal melanin concentration Cm = 1.3%, one for dark skin with a melanin concentration of 20%, and one for negroid skin with a melanin concentration of 40%. For the width of the therapeutic absorption 50 nm (FWHM) is chosen. The source width was set to a FWHM value of 20 nm, which is a typical value for LEDs. In the left panel of Fig. 4 one can see an overall decrease of the effectiveness of the therapy if the melanin content of the skin increases and the external irradiance produced by the light source remains the same. This means that a marked irradiance and dose adjustment is required for different skin types. The figure also shows that the optimum peak wavelength of the source shifts to larger values. In the right panel of Fig. 4 the effectiveness has been renormalized to 1 at a source peak wavelength of 460 nm. This eliminates the overall decrease and clearly shows the benefit of shifting the source spectrum in dependence of the skin type. For negroid skin a shift of the peak wavelength to 473 nm gives a nearly 20% better effectiveness than neglecting the effect of melanin absorption and keeping the peak wavelength at the optimum for white skin, which is near 460 nm.

The benefit of shifting the source spectrum in dependence of the melanin content of the skin increases as the width of the source spectrum is reduced. This is illustrated in Fig. 5. The therapeutic effectiveness is shown as a function of source peak wavelength for four different wavelength ranges with the following FWHM values: 100 nm, 50 nm, 20 nm and 10 nm (left panel). In the right panel, the effectiveness has been renormalized to 1 at a source peak wavelength of 460 nm. In the simulation, the width of the therapeutic absorption was 50 nm as before and the melanin concentration was set to 40%. It should be noted that the optimum peak wavelength for white skin remains near 460 nm. The relative (and absolute) effect of shifting is larger for smaller source widths, but the amount of the optimum shift itself is substantially independent of the source width. The left panel of Fig. 5 also shows that a small source width is preferred because the maximum therapeutic effectiveness will be larger.

The width of the therapeutic absorption may be considered. The larger this width, the larger the benefit of shifting the source spectrum can be. Fig. 6 shows the therapeutic effectiveness as a function of source peak wavelength for three different spectral widths of the therapeutic absorption: 20 nm, 50 nm and 100 nm. The spectral width of the source and the assumed melanin concentrations are as before. The effectiveness has been renormalized to 1 at a source peak wavelength of 460 nm. For the parameter values in this example, the optimum peak wavelength for white skin remains near 460. For a negroid skin the optimum peak wavelength is shifted and this shift increases with the width of the therapeutic absorption. For a large absorption width, the overlap between the therapeutic absorption curve and the source spectrum changes only slowly and the source spectrum can be shifted further to larger wavelengths where the transmittance of (the melanin in) the epidermis is better.

In order to tune the source emission with respect to the amount of melanin in the skin two or more individual source types may be used, possibly with spectra optimized for several different melanin concentrations. In use, the controller may operate the apparatus to activate the source type(s) with the highest effectiveness as discussed above.

To obtain a narrow band source LED units may be used (e.g. with an emission spectrum FWHM < 20 nm). Sources with very narrow emission spectra can be realized with lasers. A VCSEL (Vertical Cavity Surface Emitting Laser) is an example of a laser in a small package.

An operating scheme of an embodiment of the method is provided in Fig. 4. A spectral absorbance profile Α(λ) corresponding to a wavelength range λ and a suitable dose Dl to be administered to the body portion 1 are determined in step 17, e.g. by a practitioner. As an example, D. Barolet, "Light-emitting diodes (LEDs) in dermatology", Semin Cutan Med Surg 27:227-238 (2008), elucidates on the existence of suitable wavelengths and optimal doses or fluences for different phototherapies, dependent on the tissue and condition to be treated. An overview of conditions which may be treated with bio-stimulating phototherapy, the mechanism believed to underlie the treatment effect and the associated wavelengths is provided in the following table:

Table 1. Phototherapy condition, mechanism (proposed) & action spectrum

1. J. Liebmann, M. Born, and V. Kolb-Bachofen, "Blue-light irradiation regulates proliferation and differentiation in human skin cells", J. of Investigative Dermatology 130(2010) 259-269.

2. C.V. Suschek, C. Oplander, E.E. van Faassen, "Non-enzymatic NO production in human skin; effect of UVA on cutaneous NO stores", Nitric Oxide 22(2010)120-135. The melanin index M of the skin portion 3 of the body portion 1 is determined in step 19. This may be performed by measuring light reflectance of the skin portion 3 at one or more wavelengths and deducing the skins absorbance at the used wavelength(s). Using plural wavelengths facilitates removing contribution to the absorption by (oxy)haemoglobin and/or water.

In step 21 the absorption of light at the phototherapeutic wavelength range λ available to be used is determined and the factor Icf is calculated according to the above- reference formula.

In step 23 a suitable wavelength λ2 and a corresponding phototherapy dose D2 to be applied onto the skin portion 3 are determined based on the absorption spectrum Α(λ) and the dose Dl to be administered. For the dose, this may comprise straightforward multiplication with the correction factor Icf, e.g.: D2(D1, Icf) = D2(D1, M, λ2) = Icf(M, λ2) * Dl . More complicated calculation is also conceivable. The phototherapy dose D2 may be applied by suitable selection of illumination intensity and duration, which may comprise illumination in one or more pulses of which the pulse intensity, duration and interval may be selected.

For the wavelength λ2, an optimum balance between the emission spectrum from the apparatus ί(λ), its possible effective overlap with the absorption spectrum Α(λ) and its absorption in the epidermis by the melanin is aimed for. Generally, since the absorption of the melanin decreases with increasing wavelengths, λ2 is longer (red-shifted) than the peak absorption wavelength of the body portion 3 (where Α(λ) has its absorption maximum).

In step 25 the thus calculated phototherapy dose D2 is applied to the body portion 1 by illuminating the skin portion 3 with the wavelength λ2, resulting in

administering the suitable dose Dl .

In the calculations, the effect of heating of the epidermis by the absorbed radiation may be included with a predetermined maximum applied irradiance in order not to overheat the skin. A skin temperature of below 42°C is considered suitable, higher temperatures, in particular during prolonged periods, are undesired and temperatures of ca 45°C and higher are generally painful.

The method may be employed in separate stages, wherein the melanin index is determined at one moment and later on used for determining the function for operation of the light source, but since the melanin index may, and generally will, depend inter alia on the particular location of the skin portion and on its tanning, it is preferred to (re-)determine the melanin index shortly before applying a phototreatment.

A phototherapy apparatus 27 for use in the above described method is illustrated in Fig. 8 and may comprise a light source 29 for providing light at a bio- stimulating phototherapeutic wavelength, here comprising a plurality of sub-light sources 31 mounted to a carrier 33, a sensor 35 for determining the melanin index of a subject's skin portion 3, the apparatus being arranged for illuminating the subject's skin portion 3 with light emitted by the light source 29, the apparatus further comprising a controller 37 for controlling operation of the light source 29 as a function of the determined melanin index. The sub-light sources 31 may comprise light sources with different emission wavelengths

(colors) and/or different emission spectra (spectral width, color range, color temperature etc.) which may be individually controllable.

The apparatus 27 may be powered from any suitable power source 39, for portability powering from a battery is preferred. The controller 37 may comprise user operable knob with selectable settings. Also or alternatively, the controller may be configured to take additional input, e.g. for determining parameters of a therapy, user settings, timing, driving schemes for different skin colors etc. Advantageously, the controller is arranged, programmable or programmed for controlling operation of the light source 29 based on the Icf function discussed above. Such program may be stored on or in a memory comprised in the apparatus.

The controller 37 may also be configured for controlling operation of the light source 29 during use, possibly automated, e.g. for adaptation to skin heating, tanning, inadvertent erythema etc.

The phototherapy apparatus 27 may be a human wearable patch, such as an apparatus conforming to human physique, preferably being deformable or even pliable, indicated in Fig. 9. The patch may be maintained in position with any suitable means such as one or more adhesive portions, hook-and- loop-type fastener and/or a strap 41 closable around the body portion.

Alternatively (not shown) a phototherapy apparatus may be an assembly comprising the light source, the sensor and/or the controller as separate objects, which may be interconnected for communicating with each other, e.g. with cables or via wireless communication.

A phototherapy apparatus 27 may comprise plural sensors 35 for determining the melanin index of the subject's skin portion 3 to detect local variations of the skin portion. As shown, the light source 29 may comprise plural sub-light sources 31. Advantageously, the light source 29 comprises one or more Light Emitting Diodes or LEDs, which are available for numerous suitable wavelengths, provide significant optical output power per watt input power and generate little heat. Incoherent LEDs are considered particularly advantageous, since lasers require additional control, increasing complexity and cost of the apparatus 27 and relatively narrowband radiation poses a high risk of overheating skin. Laser radiation may also present a danger to a user's eyes.

The sensor may comprise at least one light source and at least one detector for detecting light, the sensor being configured to illuminate a subject's skin portion and detect light reflected off the subject's skin portion, wherein the sensor is configured for determining a reflectivity of the subject's skin portion at a plurality of wavelengths. This allows accurate determination of the reflectance of the skin portion and thus of determining the melanin index.

In an embodiment, a sensor, e.g. a photodiode, is integrated in the apparatus to measure the skin reflectance and/or absorbance of a user. A suitable dose for a specific application for the specific skin at a specific season or time can be obtained based on the realtime measurement results. A suitable photo-therapy scheme or algorithm may be

automatically loaded from a pre-defined storage apparatus or generated, possibly in real time, via e.g. a microprocessor that is attached to the apparatus. In such way, an effective treatment may be reached with high comfort. Alternatively, an optimal algorithm may be selected by a user via a user interface on the apparatus.

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. Features from different embodiments may be suitably combined within the scope of the appended claims, unless explicitly mentioned otherwise. "Light emitting diode" or LED includes "organic light emitting diode" or OLED. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. An apparatus (27) for bio-stimulating phototherapy, comprising a light source

(29) for providing light with a phototherapeutic wavelength, and a controller (37), wherein the controller is configured to control operation of the apparatus,

wherein the apparatus is configured for illuminating the skin (3) of a subjects body portion (1) with light emitted by the light source, and

wherein the controller is configured to control the wavelength of at least a portion of the light as a function of at least one of the melanin index (M) and the lightness (L*) of the skin.

2. The apparatus (27) of claim 1, wherein the function comprises a melanin absorption correction factor Icf = exp(Cm μ(λ) d), with:

Cm = (M-20)/150, or Cm = 1.925 - 0.44 ln(L*), μ(λ) = μ₀ λ^{"3 3} = 6.6 x 10¹¹ λ^{"3 3} cm^"1, and d is selected from a range of 0.004-0.024 cm,

wherein Cm is a measure of the concentration of melanonosomes in the epidermis of the skin portion (3), M is the melanin index, and L* is the lightness of the skin portion (3), respectively, μ(λ) is the wavelength dependent absorption coefficient of the melanin (in units of cm^"1 with λ in units of nm), and d accounts for the optical path in the epidermis (in units of cm).

3. The apparatus (27) of claim 1, wherein the light source (29) comprises one or more light emitting diodes (31).

4. The apparatus (27) of claim 1, wherein at least a portion of the apparatus is formed to conform to at least part of the subject's body portion.

5. The apparatus (27) of claim 1, comprising at least one sensor (35) for non- invasively determining the melanin index of a subject's skin portion.

6. The apparatus (27) of claim 5, comprising at least one further sensor for determining at least one further skin parameter.

7. The apparatus (27) of claim 1, wherein the apparatus is configured for providing light in a series of optical pulses with at least one of a controlled and controllable pulse repetition rate, with the pulses having a pulse irradiance and pulse duration of which at least one is at least one of controlled and controllable.

8. The apparatus (27) of claim 7, wherein the controller (37) is configured to control at least one of the pulse irradiance, the pulse duration and the pulse repetition rate as a function of time during operation of the light source.

9. The apparatus (27) of claim 1, wherein the controller (37) is programmable.

10. A method of bio-stimulating phototherapy comprising the steps of

determining a first wavelength range which is a bio-stimulating wavelength range for treatment of a subjects body portion;

determining at least one of the melanin index (M) and the lightness (L*) of the skin of the body portion;

illuminating the body portion with light having a second wavelength range; wherein the second wavelength range is modified from the determined bio-stimulating wavelength range by an amount, and

wherein the amount is determined as a function of at least one of the melanin index (M) and the lightness (L*).

11. The method of claim 10, comprising the steps of

determining a first irradiance for administering a treatment corresponding to the first wavelength range;

determining a second irradiance for administering a treatment corresponding to the second wavelength range,

wherein the second irradiance is determined as a function of the first irradiance, the second wavelength range and at least one of the melanin index (M) and the lightness (L*); and illuminating the skin of the body portion with the second wavelength range at the second irradiance.

12. The method of claim 10, comprising the steps of

determining a first phototherapy dose for administering a treatment corresponding to the first wavelength range;

determining a second phototherapy dose for administering a treatment corresponding to the second wavelength range;

wherein the second phototherapy dose is determined as a function of the first phototherapy dose, the second wavelength range and at least one of the melanin index (M) and the lightness (L*); and

providing the second phototherapy dose to the body portion by illuminating the skin of the body portion with the second wavelength range.

13. The method of any one of claims 10-12,

wherein at least one of the melanin index dependent function comprises a melanin absorption correction factor Icf = exp(Cm μ(λ) d), with:

Cm = (M-20)/150, or Cm = 1.925 - 0.44 ln(L*), μ(λ) = μ₀ λ^{"3 3} = 6.6 x 10¹¹ λ^{"3 3} cm^"1, and d is selected from a range of 0.004-0.024 cm,

wherein Cm is a measure of the concentration of melanonosomes in the epidermis of the skin portion (3), M is the melanin index, and L* is the lightness of the skin portion (3), respectively, μ(λ) is the wavelength dependent absorption coefficient of the melanin (in units of cm^"1 with λ in units of nm), and d accounts for the optical path in the epidermis (in units of cm).