GB2154761A - Diffusive optical fibre termination - Google Patents

Abstract

An optical fibre termination (1), particularly useful for laser radiation treatment of tumours, comprises a tapered end (3) to the fibre (2) and a diffusing medium (5) over the taper. The taper (3) may be uniform or non-uniform and the diffusing medium (5) may includes particulate matter to give an isotropic spread of light. <IMAGE>

Description

SPECIFICATION Diffusive optical fibre termination This invention relates to an improved optical fibre termination for use in the phototherapy treatment of tumours and other medical conditions.

The phototherapy treatment of tumours, for instance, requires that the tumour under treatment be radiated with light of selected frequency generally from a laser, the tumour having been previously administered with haematoporphryn derivative or some other activable compound.

Subcutaneous tumours undergoing this treatment require the use of optical fibres to guide the light from the source to the treatment area. in the case of many tumours the outlet termination of the fibre is inserted in the tumour with the aid of a hypodermic needle, whilst in the case where the tumour is located in passages, for example bronchial tumours, the optical fibre termination is positioned in close proximity to the tumour. Efforts have been directed in recent years to developing suitable fibre terminations to provide effective and efficient irradiation of tumours.

It is instructive to consider the prior art in this field in order to gain an appreciation of this invention.

One form of termination that has been used for these treatments is a simple cleave transverse to the fibre axis. In this instance light is issued in a cone from the core surface resulting in a highly directional output, which is usually undesirable. Further, in practice, a termination of this nature results in blood baked onto the cleaved surface during treatment due to the high intensity of light at the core's endface. The baked blood absorbs much of the light so necessitating frequent cleaning of the fibre during treatment, and complicating irradiation dosage monitoring.

Another type of termination provides that the endmost 5 to 15 millimetres of cladding be removed and the exposed core enveloped in the layer of adhesive compound mixed with diffusing matter such as sapphire powder. To protect this layer a further protective layer is generally provided by a small tube of plastics material, typically teflon. Light exits such a termination by scattering from the diffusive layer along this endmost 5 to 15 millimetres of fibre length. This type of termination is generally used for bronchial tumours, however its efficiency for this kind of treatment suffers because a significant portion of the light emerges from the end face of the fibre in a direction which does not irradiate the tumour located alongside the fibre, and further the emission from the fibre is very non-uniform along the diffusing length.

This type of termination may conceivably be used for subcutaneous tumours, however in practice the layer of diffusive material and its protective cladding results in an overall diameter which prohibits insertion by means of a hypodermic needle. This deficiency can be overcome by merely roughening the surface of the core along the endmost 5 to 15 millimetres, however such a termination has proven to be highly susceptible to breakage.

The object of this invention is to provide an optical fibre termination for use in phototherapy treatment of tumours that efficiently diffuses transmitted light and which can have a maximum diameter no greater than that of the fibre protective cladding and further which has an emitting area sufficient to prevent baking of blood onto the termination during treatment when using light powers normally used with the phototherapy treatment.

In one form therefore the invention is said to reside in a optical fibre for use in photoradiation therapy wherein the fibre comprises a central core material enveloped by cladding comprising at least one of an inner cladding of a low refractive index material and an outer cladding, the fibre being adapted to be coupled to a laser beam whereby to project laser light through the central core material having an output end portion which has a tapered core region which is surrounded by a diffusing medium whereby light emerging from the tapered core region undergoes scattering.

In a preferred embodiment the core is of circular cross-section and the diameter of the core in the tapered region decreases uniformally to a endmost point over a length of between 5 and 15 millimetres.

In a further preferred embodiment the diffusing medium comprises a transparent resin material, said resin material containing fine particulate reflective or refractive matter.

In a further preferred embodiment the diffusing medium has a cylindrical exterior surface co-axial with the fibre and having a diameter comparable to that of the fibre core.

In a further form the invention is said to reside in a method of irradiating a tumour prepared for phototherapy wherein the method includes coupling a gold vapour laser beam into an input end of an optical fibre and locating the output end in proximity to the tumour, characterized by the output end having an endmost portion which has a tapered core region surrounded by a diffusing medium whereby light emerging from the tapered region undergoes scattering.

In a preferred embodiment of this form of the invention the diameter of the tapered region decreases uniformly to an endmost point over a length of between 5 to 15 millimetres.

In a further preferred embodiment of this form of the invention the diffusing medium comprises a transparent resin material, said resin material containing fine particulate reflective or refractive matter.

Most commonly the core material optical fibres is quartz, otherwise known as silica. In this case, the taper made by one method of the invention may be prepared by controllably introducing the fibre into a dissolving environment such as hydrofluoric acid being either in the form of a solution of hydrofluoric acid or an atmosphere of hydrofluoric acid gas.

Tapered fibres have been employed in situations where optical coupling between fibres is required because a bare conically tapered termination can deliver an output with a substantially reduced divergence over conventional square-cut terminations however the specific and useful application of the invention to tumour treatment does not require a narrowly divergent beam but on the contrary requires a highly divergent beam emitted from a relatively large surface area. These two requisites are satisfied by the present invention in which the tapered core is enveloped by a diffusive medium.

In the simplest form of the termination of this invention the taper is in the form of a core typically extending over length of between 5 to 15 millimetres. However the taper may alternatively be fashioned to a non-conical form which will generally effect the irradiance from the surface of the fibre. Generally the steeper the gradient of the surface at a point on the taper the higher the intensity of light issuing at that point. The irradiance pattern from the taper may also be altered by varying the thickness of concentration of the diffusing medium along the length of the taper.

The diffusing medium may typically comprise a resin compound or silicon rubber compound impregnated with fine particulate powder so as to give a reflective or refractive effect, that is in the case of the reflective material one that has a different refractive index than the diffusing medium base.

Examples of powders are titanium dioxide or sapphire powder. It will be realised that the concentration of the powder must be chosen to provide sufficient diffusion of the emerging light without excessive absorption.

The invention will now be discussed in relation to preferred embodiments as illustrated in the accompanying drawings to assist in the understanding of the invention.

In the drawings, Figure 1 shows a tapered optical fibre.

Figure 2 shows a tapered optical fibre with a diffusive medium applied in a conical shape and Figure 3 shows a optical fibre with an alternative shape of taper and a cylindrical diffusing medium.

Now looking more closely at the drawings, it will be seen in reference to Fig. 1 that the optical fibre 1 has a cylindrical portion 2 and a tapered end portion 3. The cylindrical portion 2 is protected by a cladding 4 but the cladding is removed before the tapered portion 3.

Rays propagating within the cylindrical region are totally reflected until they reach the tapered region at which point the angle of inclination of the rays to the core surface will increase with each internal reflection until it exceeds that inclination necessary for internal reflection, where upon the ray may escape from the core material. Depending upon the degree of taper and the propagation inclination the ray may exit the core material upon first interaction with the core surface in the tapered region or may fail to exit the core material until after a multitude of internal reflections in the tapered region.

Thus light will exit the taper along its entire tapering length, however, in its naked form the irradiance emerging from the taper will be strongly anisotropic.

The fibre as shown in Fig. 1 may be inserted directly into a tumour for the delivery of laser light, however, in situations wherein the tumour is located in the side walls of an anatomical passage the anisotropic irradiance of the fibre is undesirable.

Now looking at Fig. 2 it will be seen that the tapered portion 3 of the optical fibre 1 has been coated with a diffusing medium 5 including particulate material. This diffusing medium 5 is of uniform thickness along the length of the taper and will act to scatter the emerging light in a more isotropic fashion.

Fig. 3 illustrates a non-uniformly tapered fibre end 6 having a non-uniform layer of diffusing medium 7 providing a substantially cylindrical outside surface 8 with a cylindrical diameter comparable to that of the fibre core and certainly no larger than the protective cladding 4.

The various embodiments of the invention as illustrated in Figs. 2 and 3 provide for optical fibre terminations which are robust, which are suitable for insertion by means of a hypodermic needle and which issue transmitted light uniformly along the issuing length in a generally isotropic manner and which further do not result in blood baking onto the fibre.

Claims (9)

1. An optical fibre for use in photoradiation therapy, wherein the fibre comprises a central core material enveloped by cladding comprising at least one of an inner cladding of a lower refractive index material and an outer cladding, the fibre being adapted to be coupled to a laser beam whereby to project laser light through the central core material and having an output end portion which has a tapered core region which is surrounded by a diffusing medium whereby light emerging from the tapered core region undergoes scattering.

2. An optical fibre as claimed in claim 1 in which the core is of circular cross-section and the diameter of the core in the tapered region decreases uniformly to an endmost point over a length of between 5 and 15 millimetres.

3. An optical fibre as claimed in claim 1 in which the diffusing medium comprises a transparent resin material, the resin material containing fine particulate reflective or refractive matter.

4. An optical fibre as claimed in claim 1 in which the diffusing medium has a cylindrical exterior surface co-axial with the fibre and having a diameter comparable to that of the fibre core.

5. A method of irradiating a tumour prepared for phototherapy wherein the method includes coupling a gold vapour laser beam into an input end of an optical fibre and locating the output end in proximity to the tumour, the output end having a tapered core region which is surrounded by a diffusing medium whereby light emerging from the tapered region undergoes scattering.

6. A method as claimed in claim 5 in which the diameter of the core in the tapered region decreases uniformly to an endmost point over a distance of between 5 and 15 millimetres.

7. A method as claimed in claim 5 or claim 6 in which the diffusing medium comprises a transparent resin material, the resin containing fine particulate reflective or refractive matter.

8. An optical fibre constructed and arranged substantially as herein specifically described with reference to and as shown in Fig.

2 or Fig. 3 of the drawings.

9. A method of irradiating a tumour substantially as herein specifically described with reference to and as shown in Fig. 2 or Fig. 3 of the accompanying drawings.