Apparatus for Locally Irradiating a Part of a Living Body

This invention relates to an apparatus for locally treating limited parts of a human body.

Various methods are known for locally irradiating limited parts of a living body, for example, the so-called "multiple-field irradiation" or "cross-fire irradiation" technique. In multiple-field irradiation a number of smaller fields are used in order to protect the surrounding skin and tissue and to achieve the largest possible depth dose. In cross-fire irradiation, beam cones from different incident fields which overlap at the point which is to be radiated are used. The aim is similarly to achieve a high concentration of radiation at the locally limited point which is to be irradiated, whilst the surrounding area is spared as much as possible.

With irradiation methods known hitherto it is, however, not possible to spare healthy tissue and skin in the region of the diseased focus which is to be irradiated as a locally limited point, particularly when a high concentration of energy is necessary at the focus itself in order to destroy the diseased tissue. With known methods of irradiation, impairment of or even serious damage to the surrounding healthy tissue and skin cannot be precluded.

The invention seeks to provide an apparatus for locally irradiating a part of a living body wherein a limited focus of disease can be irradiated without a substantial risk of injury to the surrounding healthy tissue and skin. In its broadest aspect, the invention essentially comprises a casing with a radiation reflective internal surface, the casing surrounding a radiation emmission point which may be coupled, for example, through a waveguide to a radiation source. The casing has an elliptic cross-section and the radiation emmission point is located at a first focus thereof. The part to be irradiated may thereby be positioned beneath an outlet aperture of the casing so that a focus of disease may be located at the second focus of the elliptic radiation reflective surface. The reflective surface is preferably ellipsoidal so that the radiation emitted at the first focus is reflected by said surface and concentrated at the second surface at the site of the disease which is to be irradiated. Thereby, almost the entire energy of the radiation from the first focus is concentrated at the site of the disease. As the energy concentration decreases with the third power of distance, the surrounding healthy tissue and skin receives only radiation of greatly reduced energy so that it is substantially undamaged.

Preferably, radiation having a wave length of from 0.1mm - 100mm, and preferably between 10mm - 100mm, is used because such radiation can be highly focused and thus concentrated precisely at the second focus of the ellipsoidal radiation reflective surface. Furthermore, radiation within this preferred wave length will penetrate to the required depth in a living body and be absorbed to such an extent that, at the second focus of the reflective surface, a sufficiently high concentration of energy is achieved to destroy the diseased tissue. The wave length used in each particular case is selected with regard to the required depth of penetration and radiation absorbtion. Since the radiation passing through the body outside the second focus is not concentrated, substantial damage to this tissue and the skin is avoided.

In a preferred embodiment, the casing comprises a series of rings which are detachably joined together. The interior surface of each ring is an annular band which forms part of the ellipsoidal reflective surface. The rings may be selectively removed to vary the distance between the second focus and a radiation exit aperture of the casing. Preferably, the casing is subdivided approximately from a central plane between the two foci, the reflective surface extending around the first focus towards the radiation exit aperture. In such an arrangement, the rings are detached to give the optimum approximation to the shortest distance between the diseased site and the skin of the body. Although less radiation will be reflected from said surface as more rings are detached, energy is still concentrated at the diseased site to give the advantages described above.

Preferably, the radiation reflective surface is conductive and is electrically connected to an earth wire. An optimum reflection factor is thereby achieved.

A waveguide, filled with a dielectric, can be disposed between a radiation source and the first focus of the ellipsoidal reflective surface. An advantage of this arrangement is that the cross-section of the bundle of rays passing from the first focus can be optimised by suitably selecting the dielectric constant of the dielectric in the waveguide depending on the local spread of the diseased site which is to be irradiated. The narrower the cross-section of the bundle, the less will be the blurring of the radiation concentrated at the second focus. The cross-sectional area of the part of the living body irradiated with a high concentration of radiation depends directly on the cross-section of the bundle of rays passing from the first focus. Advantageously, the interior of the casing is filled with a dielectric having a dielectric constant equal to, or as close as possible to the dielectric constant of a living body. This avoids radiation refraction at transition surfaces so that the radiation is accurately concentrated at the second focus. The outlet aperture of the waveguide at the first focus is preferably in the form of a horn radiator.

Therefore, it is an objection of this invention to provide apparatus for locally irradiating a part of a living body wherein a diseased site can be treated without substantial risk of injury to surrounding healthy tissue and skin.

It is a further object of the invention to provide such an apparatus where the energy of radiation is optimally concentrated at the diseased site.

It is another object of the invention to provide apparatus wherein the distance between a diseased site and a radiation outlet aperture can be easily adjusted.

It is yet a further object of the invention to provide apparatus wherein radiation of an optimum wave length can be used in an effective manner.

Further objects and advantages of the invention will become apparent from the following description of a preferred embodiment.

FIG. 1 is a cross sectional view of apparatus, according to the invention, for locally irradiating a living body.

Referring to FIG. 1, a casing 10 is provided with an ellipsoidal radiation reflective surface 12 which forms rather more than two-thirds of a complete ellipsoid. The upper portion of the casing 10 comprises a wide ring 30 and a cap 40 which is disposed on the ring 30 and has an interior forming one end of the ellipsoidal reflective surface 12.

On the side of the wide casing ring 30 remote from the casing cap 40 are connected a multiplicity of small casing rings 32, 34, 36 and 38, which are disposed close to one another in a detachable manner. The abutting edges of the individual casing parts are so shaped that when the parts are assembled the ellipsoid reflective surface formed inside the casing 10 is interrupted as little as possible.

The ellipsoid reflective surface 12 provided inside the casing 10 forms two focal points, namely a first focal point 14 and a second focal point 16. While the first focal point 14 is disposed, inside the casing, in the region of the end face of the casing cap 40, the second focal point 16 lies outside the last casing ring 38 of the multiplicity of small casing rings.

A waveguide 22 is guided through an opening in the apex of the casing cap 40 to the first focal point 14. Such outlet of the waveguide 22 may be in the form of a horn radiator. On the end of the waveguide 22 lying outside the casing 10 a radiation source 20, which may be an ultrasonic transducer, is disposed, while the end of the waveguide 22 lying at the first focal point 14 of the ellipsoid reflective surface 12 has an outlet aperture 18 for the radiation.

Both the waveguide 22 and the entire casing are filled with a dielectric 28, whose dielectric constant is as far as possible equal to the dielectric constant of a living body.

The end face of each of the small casing rings, 32, 34 36, and 38 which is remote from the first focal point 14 of the ellipsoid reflective surface 12 forms a beam passage aperture 24.

The ellipsoid reflective surface 12 is made electrically conductive and is electrically connected to an earth wire 26.

When all parts of the casing 10 shown in the drawing have been assembled, the casing 10 forms in its interior an ellipsoid reflective surface 12, 12.sup.I, 12.sup.II, 12.sup.III, 12.sup.IV which forms an ellipsoid of rotation which is complete except for the bottom ellipsoid cap extending around the second focal point 16.

When the apparatus shown in the drawing is used, the distance between the diseased focus which is to be irradiated in a living body and the skin surface of the latter on which the apparatus can be placed is first determined. As many small casing rings 38, 36, 34, 32 are then removed from the casing 10 as are required to make the distance between the second focal point 16 and the beam passage aperture 24 of the next casing ring which has not been removed correspond as closely as possible to the previously determined distance in the living body. The apparatus is then placed on the living body in such a manner that the second focal point 16 coincides as accurately as possible with the disease focus which is to be irradiated. The disease focus which is to be irradiated is then irradiated with an energy radiation of preselected wavelength and intensity for a predetermined period of time. By this means high energy absorption in the disease focus itself is achieved, while the surrounding healthy tissue does not suffer because the concentration of energy decreases from the second focal point with the third power of the distance.

The invention is defined by the following claims.