GB2331399A

GB2331399A - High intensity light source

Info

Publication number: GB2331399A
Application number: GB9723957A
Authority: GB
Inventors: Peter Brian Hart; Richard Arthur Kirk
Original assignee: PRP OPTOELECTRONICS Ltd
Current assignee: PRP OPTOELECTRONICS Ltd
Priority date: 1997-11-14
Filing date: 1997-11-14
Publication date: 1999-05-19
Anticipated expiration: 2017-11-14
Also published as: GB9723957D0; GB2331399B

Abstract

A radiation source for use in photodynamic therapy (PDT) and adapted to emit light, having a high intensity close to an emitting surface, including a densely packed two dimensional array of light emitting diodes assembled on a surface of a thermally conductive substrate 2, the density and pattern of the light emitting diodes on the substrate being such that the intensity of the light emitted by the array is uniform over an emitting surface; means for applying drive currents to each of the light emitting diodes; heat sink 5 for dissipating the heat generated by said light emitting diodes; and a housing 4 within which the light emitting diode array is located. The housing includes an output port 11 for the emitted light. The housing members and diode array each have a physical shape and size determined by a particular PDT application. The diode array is preferably of modular construction to facilitate the provision of a number of radiation sources having different physical shapes and sizes to suit particular PDT applications.

Description

2331399 - 1 HIGH INTENSITY LIGHT SOURCE The invention relates to a

radiation source for emitting light having a high, and substantially uniform, intensity close to the emitting surface thereof, and, in particular, a radiation source for use in photodynamic therapy (PDT). The invention also relates to a system for radiating a surface with high intensity light which includes a radiation source according to present invention.

PDT is a developing therapy, for the treatment of cancer and other conditions, and relies on the interaction of a specific photosensitizer with oxygen in the body, which is stimulated by high intensity light of a specific wavelength.

This therapy results is the necrosis of tumour cells in the body. Light intensities of up to 20OMWICM2 are required for this therapy and the wavelength of the light needs to be matched to the absorption characteristics of a photosensitizer used for a particular application of the therapy. Thus, high intensity light of different wavelengths are needed for the range of photosensitize rs used for this therapy.

In practice, for most of the current PIDT applications, the wavelength of high intensity light, emitted in the red region of the spectrum, needs to be in the range of 630nm to 740nm.

A number of different types of light sources have been used for PDT but, for treatment inside the body, it has been found difficult to achieve the high light intensities needed for the therapy. Lasers and fibre optic techniques have been used for delivery of the light to the area to be treated. However, with a laser, the light output is typically coupled to an optical fibre having a diameter of about 500,um, and the light delivered by the optical fibre has to be diffused and dispersed to illuminate an area, which can be from 1 CM2 to more than 30CM2 ' depending on the area to be treated. The use of lasers can give rise to a number of difficulties, including reliability and safety problems, for example, a laser beam is potentially dangerous if viewed directly. In addition, lasers for some regions of the spectrum are very expensive and require specialist personnel for their safe operation and maintenance.

With lasers, there are also problems in accurately controlling the required light output in those cases where it is necessary to treat irregular surfaces, for example, in the oral cavity. Furthermore, the output from an optical fibre is Gaussian in distribution, i.e. has a high value at the centre of the output spot, and drops off towards the edge of the illuminated area.

There is, therefore, a need for a radiation source having a high intensity uniformly distributed light output which can be adapted for use in a number of internal applications of PIDT, i.e. the treatment of internal areas of hollow organs, such as the oesophagus, and the oral cavity. A radiation source constructed from arrays of light emitting diodes, for example, as described in our UK Patent No GB 2 276 032 B, could be adapted to provide such a source for use in PIDT internal applications.

It is an object of the present invention to overcome the foregoing problems by providing a low cost, non-lasing, radiation source that is suitable for use in PIDT, i.e. the design of the radiation source, in terms of its construction, physical shape and size, is determined by particular PIDT applications for which the radiation source will be used. The radiation source includes a light emitting diode array for emitting high intensity uniformly distributed light, close to the emitting surface thereof, said light having a frequency which can be matched to the absorption characteristics of any one of the range of photosensitizers used in the therapy.

It is another object of the present invention to provide a system, for radiating a surface with high intensity uniformly distributed light which includes a radiation source of the present invention.

3 - According to a first aspect of the present invention, there is provided, a light emitting radiation source adapted to provide high intensity light close to an emitting surface thereof, including a thermally conductive substrate; a plurality of light emitting diodes assembled on a surface of said substrate in the form of a densely packed two dimensional array, said array being adapted to emit light having an intensity substantially uniform over an emitting surface thereof; means for applying drive currents to each of said light emitting diodes; heat sinking means for dissipating the heat generated by said light emitting diodes, said heat sinking means being adapted to limit a rise in temperature of said array to a predetermined level; and a housing member within which said light emitting diode array is located, said housing member including an output port, in the form of an aperture in an outer surface thereof, for said radiation source, and being of a shape and size determined by the surface area, and accessibility, of a region requiring radiation with said high intensity light. The density and pattern of said light emitting diodes on said substrate may be such that the intensity of light emitted by said array is substantially uniform over an emitting surface thereof.

The radiation source is preferably adapted for use in photodynamic therapy (PIDT), and wherein said housing member and said diode array each have a physical shape and size determined by particular applications of said PIDT.

The housing member preferably includes first connection means for connecting said diode array to a power supply and second connection means for connecting said heat sinking means to a cooling unit. The first connection means includes a length of electrical cable connected at one end thereof to said diode array and adapted to supply drive currents to each of said light emitting diodes; and an electrical connector connected to the other end of said electrical cable and adapted to be attached to, and detached from, a power supply. The second connection means includes a length of tubing connected at one end thereof to said heat sinking means and adapted to supply cooling water to said heat sinking 4 - means; and a connector unit connected to the other end of said tubing and adapted to be attached to, and detached from, said cooling unit.

According to a second aspect of the present invention, there is provided, a radiation source for use in PIDT and adapted to emit light, having a high intensity close to an emitting surface thereof, said radiation source including a thermally conductive substrate., a densely packed two dimensional array of light emitting diodes formed on a surface of said substrate, the density and pattern of said light emitting diodes on said substrate being such that the intensity of the light emitted by said array is substantially uniform over an emitting surface thereof; means for applying drive currents to each of said light emitting diodes; heat sinking means for dissipating the heat generated by said light emitting diodes, said heat sinking means being adapted to limit a rise in temperature of said array to a predetermine level; and a housing member within which said light emitting diode array is located, said housing member including an output port for said radiation source, said output port being in the form of an aperture in an outer surface of said housing member, first connection means for connecting said diode array to a power supply and second connection means for connecting said heat sinking means to a cooling unit, wherein said housing member and said diode 20 array each have a physical shape and size determined by particular applications of said PIDT.

The radiation source may be adapted to emit light having an intensity of up to 30OMWICM2, but the light intensity is preferably of the order of 20OmW/crr for the PIDT applications. The emitted light may be in the red region of the spectrum and may have a wavelength, for example, in the range 630nm to 740nm, matched to the absorption characteristics of a photosensitizer used in a particular application of PIDT. Alternatively, the diode array of the present invention may be adapted to emit light in the blue, or green, regions of the spectrum, in which case, the light intensity for the PIDT application may be in the range of 50MWICM2 to 250mWICM2, and suitable wavelengths for the PIDT application may be in the range of 430nm to 48Onm for light in the blue region of the spectrum, and in the range of 51 Onm to 54Onm for light in the green region of the spectrum. Thus, the wavelength of the emitted light may be in the range of 430= to 740nm, depending on the region of the spectrum in which the diode array is adapted to emit the high intensity light.

The heat sinking means may be adapted to limit the external temperature of the radiation source to the order of 200C to 400C.

The diode array may be of modular design, each module being in the form of a two dimensional array of light emitting diodes, in which case, combinations of the modules are adapted to provide a number of radiation sources having different physical shapes and sizes to suit particular PIDT applications.

According to a third aspect of the present invention, there is provided, a radiation source for use in PIDT and adapted to emit light, having a high intensity close to an emitting surface thereof, including a densely packed two dimensional array of light emitting diodes assembled on a surface of a thermally conductive substrate, said diode array being of modular construction to facilitate the provision of a number of radiation sources having different physical shapes and sizes to suit particular PIDT applications, the density and pattern of said light emitting diodes on said substrate being such that the intensity of the light emitted by said array is substantially uniform over an emitting surface thereof; means for applying drive currents to each of said light emitting diodes; heat sinking means for dissipating the heat generated by said light emitting diodes; and a housing member within which said light emitting diode array is located, said housing member including an output port for said radiation source, in the form of an aperture in an outer surface thereof, wherein said housing member and said diode array each have a physical shape and size determined by particular applications of said PIDT.

The housing member may be cylindrical, said two dimensional diode array being in the form of a rectangular array located within said cylindrical housing member. With this arrangement, the output port for the radiation source is formed in a side wall of said cylindrical housing member and is of a shape and size dependent on the shape and size of the emitting surface of said diode array. This radiation source may be adapted for use in PIDT, in which case, the diameter of the cylindrical housing member is adapted to enable the radiation source to be insert into a hollow organ, such as the oesophagus, requiring treatment, and the physical shape and size of said rectangular diode array is determined by an area of said organ to which said high intensity light needs to be applied.

The housing member may include a shallow box member having first and second major walls, substantially parallel to each other and separated by a number of shallow side walls; and an elongate member extending from one of said side walls to provide a handle for said radiation source. With this arrangement, an inner surface of said first major wall is adapted to support said diode array, and said output port is formed in said second major wall. The elongate member may be hollow to accommodate said first and second connection means. The longitudinal axis of said elongate member is preferably at an acute angle to the surfaces of said first and second major walls. This radiation source may be adapted for use in PIDT, the shape and size of the shallow box being adapted to enable said radiation source to be inserted into the oral cavity of a person requiring treatment and to allow said output port to be placed in close proximity to an area of said oral cavity to which said high intensity light needs to be applied.

The first and second major walls of said shallow box member may be either substantially square, or substantially rectangular, in shape.

The light emitting diodes may be in the form of GaAlAs light emitting diode chips and adapted to emit light in the red region of the spectrum, and the quantum efficiency of the GaNAs chips may be of the order of 2%. Alternatively, diode chips adapted to emit light in the red region of the spectrum may be in the form of InGaNIP light emitting diode chips. For the blue and green regions of the spectrum, the light emitting diode chips may be in the form of GainN chips.

The emitting surface of the array may be covered by a thin layer of encapsulant, such as silicone, to provide mechanical strength, and the thermally conductive substrate may be an alumina substrate.

The radiation source may include optical means for increasing the intensity of the local radiation close to the front surface of the array.

The diodes of the array may be powered by a constant current supply and the heat sinking means may include a water cooled heat sink secured in thermal contact with the substrate.

According to a fourth aspect of the present invention, there is provided, a system, for irradiating a surface with high intensity light, including a radiation source, as outlined in any of the preceding paragraphs; a power supply for the light emitting diode array of said radiation source; and a cooling unit for the heat sinking means of said radiation source.

The foregoing and other features of the present invention will be better understood from the following description with reference to the accompanying drawings, in which:

Figure 1 illustrates, in graphical form, the relative brightness scan for a light emitting radiation source of the present invention used in a PIDT application; Figures 2A to 213 diagrammatically illustrate, respectively in cross- sectional side and front elevations, a light emitting radiation source of the present invention; Figures 3 illustrates, in a cross-sectional side elevation, a scaled drawing of the light emitting radiation source illustrated in Figures 2A and 21B; Figures 4A and 413 illustrate, respectively in side and plan elevations, scaled drawings of another design for a light emitting radiation source of the present invention; and Figures 5A and 513 illustrate, respectively in side and plan elevations, scaled drawings of a further design for a light emitting radiation source of the present invention.

It will be seen from the subsequent description that the high intensity light sources provided by the present invention are constructed from arrays of LED's (Light Emitting Diodes) and are adapted for use in a number of applications, such as PDT, where it is required to radiate a surface with high intensity uniformly distributed light. In particular, it will be seen that the light emitting radiation source of the present invention has a particular use in internal applications of PDT. It will also be seen from the subsequent description that the LED arrays of the present invention are located within a housing member having an output port for the emitted light and that the output port takes the form of an aperture in an outer surface of the housing member.

The physical shape and size of the light emitting radiation source of the present invention can take many forms, i.e. the shape and size is adapted to suit particular applications, for example, PDT applications. However, in all of the designs for the light emitting radiation source, the same basic construction is used, namely, a densely packet two dimensional array of light emitting diode (LED) chips, assembled on a thermally conductive substrate, such as alumina, in a manner as described in our UK Patent GB 2 276 032 B. The LED arrays are provided with appropriate means for applying electrical power thereto, i. e. the drive currents to each of the LEDs, and heat sinking means for dissipating the heat generated by the LEDs. This can, as described in GB 2 276 032 B, be effected by using a cooled heat sink, for example, a water cooled heat sink, secured in thermal contact with the thermally conductive substrate on which the LEDs are assembled. The water cooled heat sinking arrangement is adapted to provide a good thermal environment for the LED's, and to ensure, particularly during PDT applications, that the temperature of any part of the external surfaces of a radiation source, in contact with tissue, does not exceed a temperature in the range 200C to 400C.

As described in GB 2 276 032 B, the LEDs, forming the diode arrays of the present invention, may be in the form of GaMAs LED chips, having a quantum efficiency preferably of the order of 2%, or InGaMP LED chips. These light emitting diodes are adapted to emit light in the red region of the spectrum. In addition, in order to provide mechanical strength, the emitting surface of the diode array may be covered by a thin layer of an encapsulant, such as silicone. In practice, the LED chips will typically have a quantum efficiency in the range 1 to 5%, and the drive currents to each of the LEDs will have a mean value of not greater that 100 mw. For light emitted in the green and blue regions of the spectrum, the diode arrays of the present invention, may be in the form of GainN LED chips.

An important feature of the LED arrays of the present invention is that the density and pattern of the LEDs on the thermally conductive substrate are - 10 arranged and constructed in a manner whereby the light intensity of the diode array is substantially uniform over the emitting surface of the diode array, as shown in Figure 1 of the accompanying drawings. In other words, the uniform light output of the array results from the distributed light output from individual LED chips, and the distribution of the LED chips on the substrate.

Thus, the light emitting radiation sources of the present invention are adapted to provide high radiation at the emitting surfaces of non-lasing light emitting diodes. In particular, for a 1 % efficient LED chip, emitting light in the red region of the spectrum and driven at 20mA, the resulting light output, at the front surface of the LED chip, would have an intensity of 0.36mW. With an emitting surface area Of 9Xl 0-4CM2, the light intensity at the chip face will be 90OMWICM2.

With a densely packed two dimensional LED array, at a two dimensional pitch of 0.5mm, an average light intensity of 30OMWICM2 can be obtained. In order to achieve this intensity over a useful area, it is necessary to have good thermal design for the radiation source because the total heat dissipation can be quite high, even though the drive current to the individual LEDs is not excessively high.

The LED arrays of the present invention are designed to produce uniform light outputs having light intensities to match those required for PDT. For diode arrays emitting light in the red region of the spectrum, the intensity of the light may, as stated above, be up to 30OMWICM2. However, for the PDT applications, the light intensity is preferably of the order of 20OMWICM2. In addition, the wavelength of the light output can be matched to the absorption characteristics of a photosensitizer used for a particular application of the therapy. Thus, the light output of an LED array of the present invention can be arranged to have an intensity and wavelength suitable for use in PDT. In practice, for most of the current PDT applications, the wavelength of the high intensity light output of the LED arrays of the present invention, in the red region of the spectrum, will be in the range of 630rim to 740rim.

- 1 1 - Alternatively, the diode array of the present invention may be adapted to emit light in the blue, or green, regions of the spectrum, in which case, the light intensity for the PDT application may be in the range of 50MWICM2 to 2SOMWICM2, and suitable wavelengths for the PDT application may be in the range of 430nm to 480nm for light in the blue region of the spectrum, and in the range of 51 Onm to 54Onm for light in the green region of the spectrum.

Thus, the wavelength of the emitted light may be in the range of 430nm to 740nm, depending on the region of the spectrum in which the diode array is adapted to emit the high intensity light.

As stated above, the physical shape and size of the light emitting radiation source of the present invention needs to take many forms to suit particular PDT applications. In order to facilitate manufacture of radiation sources of any required physical shape and size, the LED array of the present invention is of modular construction, i.e. is formed from a number sub-units, or modules. The physical shape and size of each of the sub-units (modules) may be the same and be such that they can be assembled to provide a number of radiation sources of different physical proportions adapted to suit particular PDT applications. In practice, each module (sub-unit) will be in the form of a two dimensional array of LEDs and adapted to be assembled in any required combination to form an LED array assembly of a required overall physical shape, i.e. have an emitting surface to match that which is required by the PDT application.

It will be seen from the subsequent description that the light emitting radiation sources of the present invention are adapted to enable the LED array assemblies to be readily attached to, and detached from, a power supply and a cooling unit, in order to make it possible for radiation sources of different shapes and sizes to be used during any one PDT treatment session.

A light emitting radiation source of the present invention, suitable for use in the PDT treatment of hollow organs, such as the oesophagus, is diagrammatically illustrated in Figures 2A and 213 of the accompanying drawings, respectively in cross-sectional side and front elevations. As illustrated in Figures 2A and 2B, the radiation source includes a hollow housing member, for the two dimensional diode array, 2, which comprises a hollow cylindrical member, 1, within which said diode array is located, and end plugs, 3 and 4. The thermally conductive substrate of the diode array, 2, is secured in thermal contact with a heat sink, 5, which is preferably provided by a water-cooled heat sink. The diode array, 2, is rectangular in shape and of modular construction, i.e. is constructed from a number of sub-units (modules). Each sub-unit (module) may, for example, be square-shaped, the sides of the square being dimensioned to match the width of the diode array, 2, and such that the length of the diode array, 2, is a multiple of the side widths. In other words, the diode array, 2, may be formed by a number of squared-shaped densely packed two dimensional LED arrays arranged in a continuous line on a thermally conductive substrate. Other sub-unit (module) configurations could be used for the diode array, 2, to accommodate different shapes and sizes for the light emitting radiation source, for example, the diode array, 2, may be divided into separate modules width- wise as well as length-wise.

An aperture, 11, in the wall of the housing member, 1, provides an output port for the emitted light, 8, from the diode array, 2. The diameter of the cylindrical housing member, 2, is determined by the size of the hollow organ, such as the oesophagus, into which the radiation source has to be inserted to effect the PDT treatment. In practice, a number radiation sources would be provided having different external dimensions to suit particular PIDT applications, i.e. the range of external dimensions selected for the radiation source would be determined by variations in the size of the treated organ(s). The actual size of a typical light emitting radiation source of the present invention, for use in internal PDT treatments, is diagrammatically illustrated in Figure 3 of the accompanying drawings.

As illustrated in Figures 2A and 213, the heat sink, 5, is connected to the end plug, 3, and to a connection assembly, 6, for supplying cooling water to the heat sink, 5, using an external water cooling unit (not illustrated). An electrical power lead, 7, is used to supply drive currents, from an external source, to each of the LEDs of the array, 2, via the end plug, 3. In order to enable a number of different radiation sources to be used, during any one PDT treatment, the connection arrangements for the cooling water and the LED drive currents are adapted for use with all of the radiation source and are arranged to be readily attached to, and detached from, the radiation sources. The connection arrangement for connecting the diode array, 2, to a power supply will, in practice, include a length of electrical cable which is connected at one end thereof to the diode array, 2, and adapted to supply drive currents to each of the light emitting diodes of the array, 2. An electrical connector (not illustrated) will be connected to the other end of the electrical cable and adapted to be attached to, and detached from, the power supply. The connection arrangement for connecting the heat sink, 5, to a cooling unit will, in practice, include a length of tubing which will be connected at one end thereof to the heat sink, 5, and adapted to supply 20 cooling water to the heat sink. A connector unit (not illustrated) will be connected to the other end of the tubing and adapted to be attached to, and detached from, the external water cooling unit.

For the PDT treatment of the oral cavity, the light emitting radiation source of the present invention must have a physical shape and size which allows the emitting surface of the LED array to be placed in closed proximity to the tissue requiring treatment, define the treatment area, and provide uniform illumination over this area. Different regions of the oral cavity may necessitate the use of differently shaped radiation sources.

- 14 One design for a light emitting radiation source, suitable for the PDT treatment of the oral cavity, is illustrated, in the form of a scaled drawing, in Figures 4A and 413 of the accompanying drawings, respectively in side and plan elevations. With this design, the light emitting radiation source includes a housing member, 9, comprising a shallow rectangular box member, 10, for the LED array (not illustrated). An output port for the emitted light, is formed as a rectangular aperture, 12, in a major wall, 13, of the box member, 10. The other major wall, 14, of the box member, 10, is substantially parallel to the wall, 13, and separated by four shallow side walls. An inner surface of the wall, 14, is adapted to support the LED array which would have a rectangular shape to match that of the output port, 12, and which would be of modular design. An elongate member, 15, extending from one of the side walls, 16, provides a handle for the radiation source. To facilitate efficient use, and manoeuverabifity, of the radiation source, the longitudinal axis of the elongate member, 15, is arranged at an acute angle to the surfaces of the major walls, 13 and 14. The elongate member, 15, is hollow in order to accommodate the connection arrangements, 18, for the supply of cooling water to the heat sink of the LED array, and for the supply of drive currents to each of the LEDs of the array. As with the radiation source of Figures 2 and 3, the connection arrangements, 18, are adapted for use with the full range of radiation sources used for the PDT treatments and are arranged to be readily attached to, and detached from, the cooling water and drive current supplies.

Another design for a light emitting radiation source, suitable for the PDT treatment of the oral cavity, is illustrated, in the form of a scaled drawing, in Figures 5A and 513 of the accompanying drawings, respectively in side and plan elevations. The only differences between the construction of this design, and that of the radiation source diagrammatically illustrated in Figures 4A and 413 of the drawings, is that the overall size of the radiation source is smaller and the shallow box member, in which the LED array is housed, is square, rather than rectangular. - is - It will be appreciated by persons skilled in the art that other

physical shapes and sizes could be used for the radiation sources, which are adapted for use in PDT treatment of the oral cavity, the main criteria being that the shape and size of the housing member is adapted to enable the radiation source to be inserted into the oral cavity of a person requiring treatment and to allow the output port to be placed in close proximity to an area of the oral cavity to which said high intensity light needs to be applied.

The radiation sources of the present invention may include optical means for increasing the intensity of the local radiation close to the front surface of the LED array.

A system, according to the present invention, for use in the treatment of cancer and other conditions, using PDT, includes a light emitting radiation source, constructed in a manner as outlined in preceding paragraphs, together with a power supply unit for the LED drive currents, and an external water cooling unit for the heat sinking means of the LED array. The cooling unit and power supply unit may conveniently be housed in a single portable unit adapted to be moved to any location where the PDT treatment is being administered. The portable unit would include means to connect it to a mains supply of electricity and have at least one set of connection ports for a light emitting radiation source, i.e. the connection ports would enable the radiation source's connection arrangements for the cooling water and the LED drive currents to be attached thereto, and detached therefrom, in a quick and efficient manner.

- 1 A -

Claims

1. A light emitting radiation source adapted to provide high intensity light close to an emitting surface thereof, including a thermally conductive substrate; a plurality of light emitting diodes assembled on a surface of said substrate in the form of a densely packed two dimensional array, said array being adapted to emit light having an intensity substantially uniform over an emitting surface thereof; means for applying drive currents to each of said light emitting diodes; heat sinking means for dissipating the heat generated by said light emitting diodes, said heat sinking means being adapted to limit a rise in temperature of said array to a predetermined level; and a housing member within which said light emitting diode array is located, said housing member including an output port, in the form of an aperture in an outer surface thereof, for said radiation source, and being of a shape and size determined by the surface area, and accessibility, of a region requiring radiation with said high intensity light.

2. A radiation source, as claimed in claim 1, wherein the density and pattern of said light emitting diodes on said substrate are such that the intensity of light emitted by said array is substantially uniform over an emitting surface thereof.

3. A radiation source, as claimed in claim 1, or claim 2, wherein said radiation source is adapted for use in photodynamic therapy (PDT), and wherein said housing member and said diode array each have a physical shape and size determined by particular applications of said PDT.

4. A radiation source, as claimed in any preceding claim, wherein said housing member includes first connection means for connecting said diode array to a power supply and second connection means for connecting said heat sinking means to a cooling unit.

17 -

5. A radiation source, as claimed in claim 4, wherein said first connection means include a length of electrical cable connected at one end thereof to said diode array and adapted to supply drive currents to each of said light emitting diodes; and an electrical connector connected to the other end of said electrical cable and adapted to be attached to, and detached from, a power supply, and wherein said second connection means includes a length of tubing connected at one end thereof to said heat sinking means and adapted to supply cooling water to said heat sinking means; and a connector unit connected to the other end of said tubing and adapted to be attached to, and detached from, said cooling unit.

6. A radiation source for use in PIDT and adapted to emit light, having a high intensity close to an emitting surface thereof, said radiation source including a thermally conductive substrate; a densely packed two dimensional array of light emitting diodes formed on a surface of said substrate, the density and pattern of is said light emitting diodes on said substrate being such that the intensity of the light emitted by said array is substantially uniform over an emitting surface thereof; means for applying drive currents to each of said light emitting diodes; heat sinking means for dissipating the heat generated by said light emitting diodes, said heat sinking means being adapted to limit a'rise in temperature of said array to a predetermine level; and a housing member within which said light emitting diode array is located, said housing member including an output port for said radiation source, said output port being in the form of an aperture in an outer surface of said housing member, first connection means for connecting said diode array to a power supply and second connection means for connecting said heat sinking means to a cooling unit, wherein said housing member and said diode array each have a physical shape and size determined by particular applications of said PIDT.

7. A radiation source, as claimed in any preceding claim, wherein said radiation source is adapted to emit light, in the red region of the spectrum, having an intensity of the order of 200mWIcm'.

8. A radiation source, as claimed in of claim 1 to 6, wherein said radiation source is adapted to emit light, in the blue, or green, region of the spectrum, having an intensity in the range 50MWICM2 to 250MW1CM2.

9. A radiation source, as claimed in claim 7, or claim 8, when appended to any of cJaims 3 to 6, wherein said emitted light has a wavelength matched to the absorption characteristics of a photosensitizer used in a particular application of PDT.

10. A radiation source, as claimed in claim 9, when appended to claim 7, wherein said radiation source is adapted to emit light having a wavelength in the range 630nm to 740nm.

11. A radiation source, as claimed in claim 9, when appended to claim 8, wherein said radiation source is adapted to emit light, in the green region of the spectrum, having a wavelength in the range 51Onm to 54Onm, or in the blue region of the spectrum, having a wavelength in the range 430nm to 48Onm.

12. A radiation source, as claimed in any of claims 1 to 6, wherein said radiation source is adapted to emit light having a wavelength in the range 430nm to 740nm, depending on the region of the spectrum in which the diode array is adapted to emit high intensity light.

13. A radiation source, as claimed in any preceding claim, wherein said heat sinking means are adapted to limit the external temperature of the radiation source to the order of 200C to 400C.

14.A radiation source, as claimed in any preceding claim, wherein said diode array is of modular design, each module being in the form of a two dimensional array of light emitting diodes, and wherein combinations of said modules are adapted to provide a number of radiation sources having different physical shapes and sizes to suit particular PIDT applications.

15. A radiation source for use in PIDT and adapted to emit light, having a high. intensity close to an emitting surface thereof, including a densely packed two dimensional array of light emitting diodes assembled on a surface of a thermally conductive substrate, said diode array being of modular construction to facilitate the provision of a number of radiation sources having different physical shapes and sizes to suit particular PIDT applications, the density and pattern of said light emitting diodes on said substrate being such that the intensity of the light emitted by said array is substantially uniform over an emitting surface thereof; means for applying drive currents to each of said light emitting diodes, heat sinking means for dissipating the heat generated by said light emitting diodes; and a housing member within which said light emitting diode array is located, said housing member including an output port for said radiation source, in the form of an aperture in an outer surface thereof, wherein said housing member and said diode array each have a physical shape and size determined by particular applications of said PIDT.

16. A radiation source, as claimed in any preceding claim, wherein said housing member is cylindrical, said two dimensional diode array being in the form of a rectangular array located within said cylindrical housing member, and wherein said output port is formed in a side wall of said cylindrical housing member and is of a shape and size dependent on the shape and size of the emitting surface of said diode array.

17. A radiation source, as claimed in claim 16, wherein said radiation source is adapted for use in PIDT, wherein the diameter of said cylindrical housing member is adapted to enable said radiation source to be insert into a hollow organ, such as the oesophagus, requiring treatment, and wherein the physical shape and size of said rectangular diode array is determined by an area of said organ to which said high intensity light needs to be applied.

18. A radiation source, as claimed in any of claims 1 to 15, wherein said housing member includes a shallow box member having first and second major walls, substantially parallel to each other and separated by a number of shallow side walls; and an elongate member extending from one of said side walls to provide a handle for said radiation source, wherein an inner surface of said first major wall is adapted to support said diode array, and wherein said output port is formed in said second major wall.

19. A radiation source, as claimed in claim 18, wherein said elongate member is hollow to accommodate said first and second connection means.

20. A radiation source, as claimed in claim 18, or claim 19, wherein the longitudinal axis of said elongate member is at an acute angle to the surfaces of said first and second major walls.

21. A radiation source, as claimed in any of claims 18 to 20, wherein said radiation source is adapted for use in PIDT, wherein the shape and size of said shallow box is adapted to enable said radiation source to be inserted into the oral cavity of a person requiring treatment and to allow said output port to be placed in close proximity to an area of said oral cavity to which said high intensity light needs to be applied.

22. A radiation source, as claimed in claims 21, wherein said first and second major walls of said shallow box member are substantially square in shape.

23. A radiation source, as claimed in claim 21, wherein said first and second major walls are substantially rectangular in shape.

24. A radiation source, as claimed in any preceding claim, wherein the light emitting diodes are adapted to emit light in the red region of the spectrum and are in the form of GaAlAs light emitting diode chips, and wherein the quantum efficiency of the GaNAs chips is of the order of 2%.

25. A radiation source, as claimed in any of claims 1 to 23, wherein the light emitting diodes are adapted to emit light in the red region of the spectrum and are in the form of InGaMP light emitting diode chips.

26. A radiation source, as claimed in any of claims 1 to 23, wherein the light emitting diodes are adapted to emit light in the blue, or green, region of the spectrum and are in the form of GainN light emitting diode chips.

27. A radiation source, as claimed in any one of the preceding claims, wherein said emitting surface of the array is covered by a thin layer of encapsulant, such as silicone, to provide mechanical strength.

28. A radiation source, as claimed in any one of the preceding claims, wherein the thermally conductive substrate is an alumina substrate.

29. A radiation source, as claimed in any one of the preceding claims, including optical means for increasing the intensity of the local radiation close to the front surface of the array.

30. A radiation source as claimed in any one of the preceding claims, wherein the diodes of the array are powered by a constant current supply.

31. A radiation source as claimed in any one of the preceding claims, wherein the heat sinking means include a water cooled heat sink secured in thermal contact with the substrate.

32. A light emitting radiation source adapted to provide high intensity light close to the emitting surface thereof, substantially as hereinbefore described with reference to the accompanying drawings.

33. A system, for radiating a surface with high intensity light, including a light emitting irradiation source, as claimed in any of the preceding claims. a power supply for the light emitting diode array of said radiation source, and a cooling unit for the heat sinking means of said radiation source.

34. A system, for radiating a surface with high intensity light, substantially as hereinbefore described with reference to the accompanying drawings.