WO2010150175A1

WO2010150175A1 - Radiation power profile, apparatus and method for phototherapy

Info

Publication number: WO2010150175A1
Application number: PCT/IB2010/052798
Authority: WO
Inventors: Giovanna Wagenaar Cacciola
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2009-06-26
Filing date: 2010-06-21
Publication date: 2010-12-29

Abstract

A method, a radiation power profile (P M (t)) and an apparatus for phototherapy of tissue are provided, in or by which a first pulse (8) of radiation with a phototherapeutic wavelength is applied to the tissue. The emitted power level of the first pulse is controlled to apply a radiation dose to the tissue with a predetermined radiation power profile (P M (t)). The first pulse comprises at least a first power level (P 8A ) for a first portion (T 8A ) and a second power level (P 8B ), different from the first, for a second portion (T 8B ) of the first pulse. The first and second power levels define at least a portion of said radiation power profile. A series of micropulses (9) is provided to obtain and define the first pulse (8) as a macropulse (8). The micropulses have a number of pulse parameters selected from a group comprising pulse power (P m ), pulse power density (p m ), pulse energy (E m ), pulse duration (T m ) and interpulse interval (DT µ ). A variation of at least one of said pulse parameters in at least a portion of said series of micropulses is controlled to define said predetermined radiation power profile (P M (t)) of said macropulse.

Description

Radiation power profile, apparatus and method for phototherapy

TECHNICAL FIELD

The invention relates to treatment of tissue with radiation, in particular phototherapy of human skin, e.g. photocosmetic therapy.

BACKGROUND

Human tissue may be treated with light for medical or cosmetic purposes. E.g. US 4,930,504 discloses a device for biostimulation of tissue and a method of treatment of tissue comprising exposing the treated tissue to the device. The device of US 4,930,504 comprises an array of substantially monochromatic radiation sources of a plurality of wavelengths, preferably of at least three different wavelengths. The radiation sources are arranged within the array such that radiation of at least two different wavelengths passes directly or indirectly through a single point located within the treated tissue. The radiation sources may be laser diodes, superluminous diodes or similar light-emitting diodes that, while low-power radiation sources, can provide significant energy densities to a treatment area. The device may be included within a system with a control panel, a power source, means for varying pulse frequency, means for varying pulse duration, means for timing the period of treatment, means for measuring the conductivity of the treated tissue, means for measuring the optical power emitted by the radiation sources and/or means for detecting emissions from the radiation sources. The method is successful against pain from different causes.

Further, US 2009/0018621 discloses a medical and/or cosmetic radiation device which has a plurality of LEDs which emit radiation pulses at different wavelengths. The device may comprise an electronic control with which the time sequence of the radiation of individual LEDs is selectively controllable. US 2009/0018621 discloses that depending on the application the effect achieved with a first wavelength, which is optimal at a shorter pulse length and higher intensity, may be combined with another radiation of a second wavelength, which displays an optimal effect at a longer pulse length but lower intensity. SUMMARY OF THE INVENTION

In order to improve the efficiency of phototherapy the present method, radiation power profile and apparatus are provided.

The method for phototherapy of tissue comprises the step of applying a first pulse of radiation with a phototherapeutic wavelength to the tissue, wherein the emitted power level of the first pulse is controlled to apply a radiation dose to the tissue with a predetermined radiation power profile. The first pulse comprises at least a first power level for a first portion of the first pulse and a second power level, different from the first power level, for a second portion of the first pulse. The first power level and the second power level define at least a portion of said radiation power profile. The method comprises the step of providing a series of micropulses to obtain the first pulse as a macropulse defined by at least said series of micropulses, which micropulses have a number of pulse parameters selected from a group comprising pulse power, power density, pulse energy, pulse duration and interpulse interval. A variation of at least one of said pulse parameters in at least a portion of said series of micropulses is controlled to define said predetermined radiation power profile of said macropulse.

Correspondingly, a radiation power profile is provided which is arranged for a phototherapy light pulse and which comprises at least a first power level for a first portion of the pulse and a second power level, different from the first power level, for a second portion of the pulse. The radiation power profile is defined as a macropulse by a series of micropulses as mentioned hereinbefore.

Further, an apparatus for phototherapy of tissue is provided which comprises a source of radiation configured to emit a first pulse of radiation with a phototherapeutic wavelength to the tissue and which comprises a controller configured to operate the source of radiation to provide a macropulse defined by a series of micropulses as mentioned hereinbefore.

The controller is programmed to operate the source of radiation to emit a first pulse of radiation with a predetermined radiation power profile, wherein the first pulse comprises at least a first power level for a first portion of the first pulse and a second power level, different from the first power level, for a second portion of the first pulse, wherein the first power level and the second power level define at least a portion of said radiation power profile.

A radiation power profile may be stored in the controller or associated memory of an apparatus for phototherapy as an executable program or a set of parameters defining the radiation profile and cooperating with a program in the controller. The radiation profile, as a program or set of parameters, may be downloaded from external storage media such as USB memory or IT services such as network servers to the apparatus for phototherapy via wired or wireless connections. Multiple radiation power profiles may be stored in the apparatus for phototherapy and selectable from a user interface associated with the apparatus for phototherapy. This user interface may be integrated in the phototherapy apparatus or implemented as a wired or wireless add-on to the apparatus.

It has been found that the efficiency of phototreatment depends on the applied dose and the intensity of the radiation. Moreover, it has been found that biological tissue, in particular human skin, may adapt to phototherapeutic radiation. The method therefore allows improving efficiency of the treatment. Varying the phototherapy power level of the first pulse in accordance with the radiation power profile allows optimizing the phototreatment to the absorption capabilities of (the tissue of) the treated subject and administering a desired dose of radiation energy to the tissue with increased effectivity. Possible discomfort of a treated subject due to (exposure to) a high radiation power level and/or a prolonged exposure to the radiation may be avoided. Operation of the source of radiation of the apparatus to emit a first pulse of radiation according to the radiation power profile allows to reduce energy consumption of the apparatus thus rendering the apparatus more efficient. In particular in a battery-operated device this may enable prolonged operation and therewith improve user- friendliness.

Administering the first pulse as a macropulse defined by a series of micropulses facilitates control of the power levels defining the radiation power profile of the first pulse. It further facilitates using and/or correcting for variations of properties of the light source during administering the first pulse. Pulsed operation of the light source also reduces thermal load on the light source which may assist stabilizing performance of the apparatus. E.g. solid state light sources, such as LEDs, generally have increased electrical-to -optical efficiency but tend to be more sensitive to an increased light source temperature compared to incandescent lights and general flash lights. Solid state light sources such as LEDs are generally more responsive to variations in the driving power of the light source (e.g. driving current) than other light sources and thus their operation may be more reliably controlled than incandescent lights. They may also be more readily configured or configurable to provide a particular radiation wavelength.

These and other aspects will be apparent from and elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like features may be identified with like reference signs. In the drawings: Figs. 1-3 are schematic indications of radiation pulses having different but constant radiation power levels;

Figs. 4-7 are schematic indications of radiation pulses having improved radiation power profiles;

Figs. 8-13 are schematic indications of radiation pulses having improved radiation power profiles defined by series of micropulses with varying micropulse parameters.

DETAILED DESCRIPTION OF EMBODIMENTS

The Figs, show schematic representations of radiation pulses, with time plotted on the ordinate in seconds [s] and power plotted on the abcissa in Watt [W]; units are denoted in square brackets []. Where in the following power is considered (in Watt), power density may be equally considered (in Watt per cm² irradiated surface area [W/cm²]), taking the irradiated area and the irradiation intensity distribution over the irradiated area as constants within the present context. It should be noted that within the present context "phototherapy" or

"phototreatment" means irradiating a tissue to be treated with radiation which may also be referred to as light and which may have a wavelength in the range from about 1 micrometer [μm] (infrared or IR) through visible wavelengths to ultraviolet (UVA) at about 350 nanometers [nm]. An applied radiation wavelength is considered to be substantially monochromatic when having a centre wavelength within the above-referenced wavelength range and having a spectral width of about ± 20 nm from that centre wavelength. Various light sources may be utilized for generating such radiation; high power lamps, flash lights, lasers, light-emitting diodes etc. Particular light sources such as superluminous LEDs or lasers may, however, provide light with a much narrower spectral width which may in some cases be even in the range of about ± 1 nm about a centre wavelength.

Within the present context, "therapy" or "phototherapy" may be of cosmetic or curative nature. Conditions suitable for such phototreatment include skin rejuvenation, acne, atopic eczema, psoriasis, vitiligo, inflammations, wound healing, pain, etc. Different conditions may benefit from radiation with different (combinations of) treatment wavelengths, which may address different biochemical processes, e.g. triggering cell growth or rather apoptosis.

A phototherapeutic treatment may comprise one or more treatment sessions, which may comprise administering one or more radiation pulses to a portion of tissue. Generally, within a treatment session pulses are administered on adjacent or possibly slightly overlapping portions of tissue.

It has been found that biochemical process may require a threshold or critical power level P_cπt for initiation and are not initiated in case of too little applied power, irrespective of the duration of the pulse. A pulse 1 with a constant too low power level Pi over its duration Ti is shown schematically in Fig. 1. To be therapeutically effective, a pulse 2 with an increased power level P₂, higher than the threshold value P_cπt should be applied (see Fig. 2), which may have a shorter pulse length T₂ to contain the same pulse energy E (in Joule [J]) as the pulse 1 of Fig. 1.

In order to apply the same amount of pulse energy E to the tissue while reducing the duration of discomfort to the subject, a pulse 3 may be applied with a much higher pulse energy P₃ and a shorter pulse length T₃, see Fig. 3. However, such high pulse power may exhibit adverse effects on the tissue. It has been found that a therapeutic dose of phototreatment radiation may cause adverse effects, discomfort or even pain, in particular when applied to a sensitive body point. Fig. 4 schematically indicates a phototherapy radiation pulse 4 which accounts for adaptation of the treated tissue to the radiation. The pulse 4 has a time- varying radiation power profile P₄(t) with the same integrated energy content or dose E as the pulses 1 -3 shown in Figs. 1-3. The radiation power profile P₄(t) is defined by a first portion T₄A of the duration of the pulse 4 comprising a first power level P₄A and a second portion T₄B of the pulse 4 comprising a second power level P₄B which is lower than the first power level P₄A. The first power level P₄A is selected to initiate an intended biochemical process in the tissue to be treated and is higher than the threshold value P_crit. Once the process is initiated, the lower power level P₄B is sufficient to sustain the process. E.g. a portion of the tissue may be heated to a desired value and subsequent radiation need only compensate for heat loss of the irradiated area. Thus, the tissue (and thus the treated subject) is exposed to a power level which is bioefficient and reduces chances of adverse effects, e.g. overheating. Possible discomfort associated with the phototherapy can be reduced or even prevented.

Since operating a light source at decreased output power generally requires much less input power than would be expected from a linear decrease of input power with output power of the light source itself, generating a pulse 4 with the shown radiation power level generally is more efficient than generating a pulse with a constant high power level, e.g. as in Figs. 2 and 3. Providing a lower power level of the second portion (P_4B, T_4B) of the pulse 4 thus may outweigh a longer total duration of the pulse 4 to administer the same energy dose E. Thus, in a battery operated apparatus the battery charge may last for more pulses.

Fig. 5 schematically indicates another option for a phototherapy radiation pulse with which adaptation of the treated tissue to the radiation may be taken into account. The pulse 5 has a time-varying radiation power profile Ps(t) during the pulse, wherein the radiation power profile Ps(t) is defined by a first portion T_SA of the duration of the pulse 5 comprising a first power level P_SA and a second portion T_5B of the pulse 5 comprising a second power level P_SB which is higher than the first power level P_SA- The pulse 5 is particularly suited for conditions in which the tissue adapts to the applied radiation during the treatment pulse and a higher power level P_SB can be effectively absorbed by the tissue, e.g. blood flow to a portion of the skin may increase in a few seconds. In other words, with (the radiation power profile Ps(t) of) the pulse 5 the tissue may be prepared by the first portion (P5A, T_5A) of the pulse 5 for the higher effective dose of the second portion of the pulse 5 (P₅B, T_5B). Again, the skilled person will appreciate that the pulse 5 having the same pulse energy is more bio -efficient (biologically) and more energy efficient (input power) than a pulse having a substantially constant power level as in Figs. 1-3.

Since biological processes may develop rather gradually, a pulse 6 with the radiation power profile P₆(t) shown in Fig. 6 may be applied. The radiation power profile Pβ(t) is defined by a first portion T₆A with a first power level P₆A and a second portion T₆B with a second power level P₆B which is lower than the first power level P₆A, and it is defined further by a third portion T₆c with a third power level Pec in between the first power level P₆A and the second power level P₆B- The pulse 6 provides a more gradual radiation power profile Pβ(t) in accordance with gradual adaptation of the tissue.

In Fig. 7 a pulse 7 is shown, being a variant of the pulse 6; in the pulse 7, the difference between the first power level P₇A and the third power level P₇c is significantly larger than the difference between the second power level P₇B and the third power level P₇c. The first portion of the pulse 7 can trigger the intended process and the second and third portions are configured to correspond to the adaptation of the tissue.

A gradual pulse power profile may also be used with a an increasing power level during the pulse. The increase or decrease may also have more power levels or be continuous, without the first, second and/or third power level being a constant power level. In such case, one or more different power level gradients may be identified within the pulse.

Fig. 8 is a schematic indication of an embodiment of two substantially identical pulses, wherein the radiation power profile is defined as a macropulse 8 by a series of micropulses 9. Each micropulse 9 has a number of pulse parameters such as (micro-)pulse power P_μ_[W], (micro-)pulse power density p_μ [W/cm²], (micro-)pulse energy E_μ [J], (micro-)pulse duration T_μ[s] and (micro -)interpulse interval ΔT_μ[s]. Each macropulse has a time-varying macropulse radiation power profile P_M(O [W] and power density profile P_M(O [W/cm²], a macropulse energy E_M [J], a macropulse duration T_M [S] and a macropulse interval ΔT_M [S], defined by appropriately controlled micropulse parameters. E.g., the macropulse energy E_M is the sum of the micropulse energies E_μ of the micropulses 9 defining the macropulse 8, the macropulse power level P_M [W] at a given time t is the running time average of the micropulse power P_μ of a number, e.g. two, three, five or ten consecutive micropulses 9 centered about that time t. In the macropulses 8 of Fig. 8 the pulse parameters of the micropulses 9 are controlled to provide a series of micropulses 9 with substantially equal duration T_μ at a constant interpulse interval ΔT_μ but having varying power P_μ such that the micropulse energy E_μ varies over the macropulse 8. Thus, a time varying envelope radiation power profile P_M(O of the macropulse 8 is provided which is similar to that of Fig. 7. Since pulse parameters of one or more individual micropulses 9 may be accurately defined in an appropriately programmed apparatus, detailed control over the radiation power profile P_M(O of the macropulse 8 is facilitated and the power level may be finely adjusted to the adaptation of the skin.

A more complex macropulse 8 is indicated in Fig. 9. This pulse has a radiation power profile P_M(O, defined by a series of micropulses 9 and comprising a plurality of power levels P. The micropulse powers P_μ are controlled to provide in the power profile P_M(O of the macropulse 8 a first power level gradient G_IOA from a first power level P_IOA (here 0 W) to a second, higher, power level P_IOB during a first portion T_IOA of the macropulse duration, a second power level gradient G_IOB of zero at a constant second power level P_IOB during a second portion T₁₀B, a third power level gradient doc to a third power level Pioc and fourth power level gradient G_IOD to a fourth power level P_IOD (here 0 W, again), during third and fourth portions T_1Oc, T₁₀D, respectively. Each of the power level gradients in this example is different. A pulse with such radiation power profile may be used for treating a delicate portion of tissue; during the initial portion (G_IOA, T_IOA) the tissue is pretreated, the targeted biochemical processes, e.g. for skin healing, are initiated and the skin adapts to the treatment. During the second portion (G₁₀B, T_1OB) the full treatment radiation energy is administered. However, during this second portion the treated subject may experience some discomfort and the pulse is gradually ended with an accelerating power level decrease (G_1Oc Tioc; G₁₀D, T_1OD) SO as to administer maximum total radiation energy with minimum discomfort.

Figs. 10-13 indicate different ways of variation of micropulse parameters to define macropulse radiation power profiles. Fig. 10 indicates a portion of a treatment session comprising three macropulses 8A, 8B and 8C. In Fig. 10, similar to Fig. 8, the micropulse energy E_μ is varied between consecutive micropulses 9, whereas the micropulse duration Tμ and pulse interval ΔT_μ are kept constant. Within each macropulse 8A-8C and between consecutive macropulses 8A-8B, 8B-8C the radiation power level of the micropulses 9 and thus of the macropulses is increased. Thus, a gradual increasing envelope power level from a first power level to a second power level is provided for each macropulse 8A-8C, indicated with a drawn line. Further, the micropulse parameters of the last micropulse 9 of the first shown macropulse 8 A and the first micropulse 9 of the second shown macropulse 8B are set identical, such that the first power level of the second macropulse 8B is identical to the final power level of the first macropulse 8A (see the broken line between pulses 8A-8B). In contrast, the micropulse parameters of the series of micropulses 9 of the second shown macropulse 8B and of the third shown macropulse 8C are controlled such that the power level between the second and third macropulses 8B, 8C continues as if the applied power were not interrupted in between these macropulses (see the broken line between pulses 8B- 8C). Different treatment regimens may be contemplated, depending inter alia on the (portion of) tissue and/or the condition to be treated.

Fig. 11 indicates two substantially identical consecutive macropulses 8 being defined by a series of micropulses 9. In Fig. 11, the pulse parameters of the micropulses are controlled to keep the pulse power P_μ and the duration T_μ of the micropulses, and thus the micropulse energy E_μ, constant throughout the series. However, the interpulse interval ΔT_μ(t) between consecutive micropulses is continuously decreased, providing a macropulse with a nonlinear increasing radiation power profile P_M(O (schematically indicated with the drawn curves, not to scale).

Fig. 12 also indicates two substantially identical consecutive macropulses 8. In Fig. 12, the pulse parameters of the micropulses are controlled to keep the interpulse interval ΔT_μ between consecutive micropulses and the pulse power P_μ constant, but to increase the duration T_μ(t) of the micropulses, and thus the micropulse energy E_μ, throughout the series. Thus, macropulses 8 with a nonlinearly increasing radiation power profile P_M(O are defined (schematically indicated with the drawn curves, not to scale).

In Fig. 13 a single macropulse is indicated. The macropulse has a nonlinearly increasing radiation power profile defined by a series of micropulses which have a substantially constant micropulse power P_μ and which start at constant intervals Δt_μ, but which have increasing pulse duration T_μ(t) and therefore decreasing interpulse interval ΔTμ(t). Thus, a macropulse with a linearly increasing radiation power profile P_M(O is defined (schematically indicated with the drawn curve, not to scale).

Combinations of a plurality of such radiation power profiles may be made. As a comparative example, consider an apparatus for treatment of a portion of skin, which apparatus gives a single macropulse defined by a series of 100 micropulses. The micropulse duration is set constant at T_μ = 250 ms and the interval between the micropulses is set constant at ΔT_μ = 100 ms, giving a total treatment time of T_M = 35 s. The power density administered to the skin by the apparatus during each micropulse is set constant at p_μ = 4 mW/cm². Keeping all micropulse parameters constant as stated during the treatment, a macropulse with a constant radiation power profile is provided delivering a total energy density to the skin of (power density) x (total time of the micropulses) = 4 [mW/cm²] x 250 [ms] x 100 [pulses] = 0.1 J/cm².

In phototreatment for rejuvenation of human skin a more pronounced effect may be reached by increasing the power density during the treatment. According to the following embodiment the power level of the phototreatment is increased in a gradual way and the skin is allowed to get used to the treatment. Starting from the same parameters as in the comparative example above, the micropulse power density level is increased 0.5 mW/cm² every 20 pulses (which may be considered a combination of the macropulses of Figs. 8 and 10), such that the power density p_μ delivered in the last 10 micropulses 9 of the macropulse 8 is 50% more than that of the initial micropulses 9, i.e. at the end of the treatment p_μ = 6 mW/cm² per micropulse instead of p_μ = 4 mW/cm². With a macropulse radiation power profile P_M(T) having these specifications the total energy density delivered by the macropulse to the skin is given by p_M(total) = Σ_μ-_puises(Pμ) = (4 x 250 x 20) + (4.5 x 250 x 20) + (5 x 250 x 20) + (5.5 x 250 x 20) + (6 x 250 x 20) [mW/cm² x ms x pulses] = 0.125 J/cm². Thus, a quarter more energy is usefully administered to the skin in the same treatment duration compared with the comparative example. Increasing output radiation power may be effected by increasing a driving current in LED light sources, the presently provided apparatus can accordingly comprise a programmed controller for operating a LED driving current.

As an alternative to the previous example, a variant of the radiation power profile embodiment of Fig. 13 may be used, keeping the power density constant at p_μ = 4 mW/cm² and increasing the duration of the micropulses T_μ and simultaneously reducing the interpulse interval between the micropulses ΔT_μ, such that the total treatment time may be maintained at a macropulse duration of T_M = ∑_μ-_Puises(T_μ + ΔT_μ) = 35 s. Instead of increasing the duration of the micropulses T_μ for each individual micropulse, the increase is controlled to occur for a number of consecutive micropulses such that the macropulse comprises sub- series of micropulses with identical micropulse parameters, with each sub-series comprising gradually decreasing numbers of micropulses: (4 x 250 x 20) + (4 x 350 x 16) + (4 x 400 x 15) + (4 x 450 x 15) + (4 x 500 x 15) [mW/cm² x ms x pulses] = 0.123 J/cm². Pulse duration and/or pulse interval are also readily controllable for an apparatus comprising a controller having a clock functionality. A single macropulse 8 may comprise a few tens of micropulses 9, e.g. 10, 15,

25 or 50 to several tens of thousands of micropulses 9. Consecutive macropulses may be defined by repeating patterns of micropulse parameter variations, defining repeating radiation power profiles, which may be scaled with respect to each other (cf. pulses 8A-8C in Fig. 10). Consecutive macropulses may be separated by a period of absence of micropulses of about the same duration as the preceding series of micropulses or of about an order of magnitude larger than the average duration of two consecutive micropulses T_μ and corresponding micropulse intervals ΔT_μ, e.g. more than 25 or 50 times the average duration of two consecutive micropulses T_μ and corresponding micropulse intervals ΔT_μ.

As a further example, an apparatus may comprise a plurality of light sources, e.g. 100 LEDs which may be arranged in a regular fashion such as in an array of 10 rows of 10 juxtaposed LEDs, which light sources are operated with a radiation power profile as described herein and according to a predetermined spatial and/or temporal pattern over the plurality of light sources. This may reduce sensations of discomfort by the treated subject, since it has been found that perception of temperature and/or pain is dependent on the affected area. Variations in sensitivity of portions of the irradiated area, e.g. painful or inflammed spots, may also be taken into account. The switching pattern may be spatially and/or temporally repetitive, e.g. in a linear or circular wave-like sequence. 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.

For example, shown radiation power profiles may be time-inverted. It is further possible to operate the present teaching in an embodiment wherein plural radiation power profiles are juxtaposed. Whereas the present examples have been presented for a single wavelength as defined above, a combination of wavelengths may be utilized in phototherapy. E.g., for skin rejuvenation a combination of wavelengths of 870 nm ± 20 nm (near-infrared) and 590 nm ± 20 nm (amber) is most efficient. In a phototherapy, one or more wavelengths may be operated according to the claimed method. Different wavelengths may be operated according to different radiation power profiles to achieve maximum effect. E.g., to initiate complex series of interrelated processes complex radiation power profiles may be required; healing of deep skin wounds or scars may require stimulation of different types of skin tissue which each require different radiation power profiles. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single 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. Method for phototherapy of tissue comprising the step of applying a first pulse

(8; 8 A; 10) of radiation with a phototherapeutic wavelength to the tissue wherein a series of micropulses (9) is provided to obtain the first pulse (8; 8A; 10) as a macropulse (8; 8 A; 10) defined by at least said series of micropulses wherein the emitted power level of the first pulse is controlled to apply a radiation dose (E) to the tissue with a predetermined radiation power profile (P_M(T)), wherein the first pulse comprises at least a first power level (P_SA; P_IOA) for a first portion (T₈A; T₁OA) of the first pulse and a second power level (PSB; PIOB) for a second portion (T₈B; T₁OB) of the first pulse, and wherein the second power level is different from the first power level and wherein the first power level and the second power level define at least a portion of said radiation power profile. wherein said micropulses have a number of pulse parameters selected from a group comprising pulse power (P _μ), pulse power density (p_μ), pulse energy (E_μ), pulse duration (T _μ) and interpulse interval (ΔT_μ), wherein a variation of at least one of said pulse parameters in at least a portion of said series of micropulses is controlled to define said predetermined radiation power profile (P_M(O) of said macropulse.

2. The method of claim 1 , wherein the first power level (P_SA; P_IOA) is lower than the second power level (PSB; PIOB).

3. The method of claim 1, wherein the first power level (P_SA; P_IOA) is higher than the second power level (PSB; PIOB).

4. The method of claim 1 , wherein said radiation power profile (P_M(O) comprises a third power level (Pioc) in between the first power level and the second power level, wherein the radiation power profile comprises a first power level gradient (Gi _OA) between the first power level and the third power level and a second power level gradient (Gi oc) between the second power level and the third power level, different from the first power level gradient.

5. The method of claim 1, comprising the step of applying at least a second pulse (8B) of radiation with a phototherapeutic wavelength to the tissue, wherein the emitted power level of the second pulse is controlled to apply a radiation dose (E) to the tissue with a predetermined second radiation power profile (P_M(T)), wherein the second pulse comprises at least a first power level (P_SA; P_IOA) for a first portion (T₈A; TIOA) of the second pulse and a second power level (PSB; PIOB) for a second portion (T₈B; TIOB) of the second pulse, wherein the first power level and the second power level define at least a portion of the second radiation power profile, and wherein at least one of the first power level and the second power level of the second pulse is different from the first power level and the second power level of the first pulse (8A).

6. A radiation power profile (P_M(O) arranged for a phototherapy light pulse comprising at least a first power level (PSA; PIOA) for a first portion (T₈A; TIOA) of the pulse and a second power level (PSB; PIOB) for a second portion (T₈B; TIOB) of the pulse, wherein the second power level is different from the first power level said radiation power profile being defined as a macropulse (8; 8A; 10) by a series of micropulses (9), which micropulses have a number of pulse parameters selected from a group comprising pulse power (P_μ), pulse power density (p_μ), pulse energy (E_μ), pulse duration (T_μ) and interpulse interval (ΔT_μ), wherein said predetermined radiation power profile is defined by a controlled variation of at least one of said pulse parameters in at least a portion of said series of micropulses.

7. The radiation power profile (P_M(O) of claim 6, wherein said radiation power profile comprises a third power level (Pioc) in between the first power level (P_SA; PioA)and the second power level (PSB; PIOB), wherein the radiation power profile comprises a first power level gradient between the first power level and the third power level and a second power level gradient (Gioc) between the second power level and the third power level, different from the first power level gradient.

8. An apparatus for phototherapy of tissue comprising a source of radiation configured to emit a first pulse of radiation (8; 8 A; 10) with a phototherapeutic wavelength to the tissue and comprising a controller configured to operate the source of radiation wherein the controller is programmed to operate the source of radiation to emit a first pulse of radiation with a predetermined radiation power profile (P_M(T)), and to operate the source of radiation to provide a series of micropulses (9) to obtain the first pulse (8; 8 A; 10) as a macropulse defined by said series of micropulses wherein the first pulse comprises at least a first power level (P_SA; P_IOA) for a first portion (T₈A; T₁OA) of the first pulse and a second power level (PSB; PIOB) for a second portion (T₈B; T₁OB) of the first pulse, and wherein the second power level is different from the first power level and wherein the first power level and the second power level define at least a portion of said radiation power profile wherein said micropulses have a number of pulse parameters selected from a group comprising pulse power (P _μ), pulse power density (p_μ), pulse energy (E_μ), pulse duration (T_μ) and interpulse interval (ΔT_μ), and to control a variation of at least one of said pulse parameters in at least a portion of said series of micropulses to define said predetermined radiation power profile of said macropulse.