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Description  |
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BACKGROUND OF INVENTION
This invention relates to a fiber optic device and more particularly to a
device for dispersing light propagating along an optical fiber into an
approximately uniform cylindrical pattern surrounding the fiber, and a
method to manufacture this device.
During the course of the last several years, a new method of treatment for
cancer in humans has been receiving considerable attention. Known as
"photodynamic therapy" (PDT), this treatment makes use of two
well-documented effects to destro cancerous tissues. The two effects are:
(1) the propensity of certain chemicals to concentrate (or to remain)
preferentially in cancer cells, and (2) the ability of light with a
specific wavelength to promote photochemical reactions which, in the
absence of such light, would proceed extremely slowly or not at all. The
first effect is the foundation of the entire field of chemotherapy in
which more or less "poisonous" chemicals are introduced into the patient.
It is desired that lethal doses of the chamical concentrate in the cancer
cells while non-lethal doses are received by normal cells. The second
effect underlies the entire field of photochemistry in which light
promotes many reactions not otherwise occurring. The fields of
photography, photosynthesis, vision, etc. are common examples of light
causing chemical reactions to proceed.
PDT combines these two effects in the treatment of cancer. A mixture of
chemicals known as "hematoporphyrin derivative" (HpD) is widely known to
remain preferentially in cancer cells. As extracted from serum, HpD
fluoresces when exposed to light. This has proven to be a valuable
diagnostic tool for many kinds of cancer. However, it has also been
observed that, when illuminated with light of a specific wavelength and in
sufficient intensity, HpD undergoes a photochemical reaction and kills the
cell in which it resides. The exact nature of the chemical reaction which
leads to the death of the host cell is not precisely defined and is the
subject of continuing research at many institutions. However, the effect
of killing the host cell is well-documented and is finding increasing use
as a cancer treatment in the U.S. and elsewhere.
In clinical use, a patient is injected with HpD in an appropriate dosage as
determined by the attending physician. The HpD permeates cells throughout
the body, but dissipates from normal cells much more rapidly than from
cancer cells. Typically, 48 to 72 hours after injection, HpD will remain
in the patient's cancerous cells in much greater concentrations than in
the surrounding normal tissue. Thus, exposing the cancerous region during
this sensitive period to suitable light (for HpD this is red light with
wavelength close to 630 nanometers) of sufficient intensity (as determined
by the physician considering such things as the depth of the tumor, its
nature, location, orientation etc.) will lead to preferential destruction
of the cancerous tissues exposed to light.
PDT has several attractive features. HpD by itself is not a "poison". Thus,
unlike much conventional chemotherapy, the patient has virtually no
discmforting side effects from the treatment. (However, the patient is
overly sensitive to light and is advised to stay out of sun light for
several weeks following treatment.) PDT does not interfere with other
modes of treatment. It can be readily used as part of a whole range of
treatments the physician may prescribe for the patient. Most attractive of
all, PDT is the first definite example of a method of cancer treatment
combining photochemistry with preferential concentration in cancer cells.
Since both effects are known to be widespread, HpD will almost certainly
not be the last treatment to work in this manner.
However, some problems remain with PDT. The treatment is not effective
unless suitable intensity of light is brought to bear upon the tumor.
Thus, for cancers that rapidly spread over great areas, rapidly invade
tissues deeply, or otherwise cannot be reached with light, PDT may not be
the method of choice for the physician.
The present invention concerns a device which allows the physician to
effectively deliver intense light to certain tumor sites not otherwise
conveniently reached. The device must be capable of carrying intense
radiation without overheating and destroying itself. The device must
provide a uniform pattern of illumination so the physician can irradiate
the entire treatment area with intense radiation lethal to the cancer
cells, without leaving "dark areas" of undestroyed cells to cause future
problems for the patient.
For cancers occurring in tubular regions of the body, the appropriate
pattern of radiation for treatment is a uniform cycylindrical pattern.
Thus, for PDT treatment of esophogeal cancer, an optical fiber is required
to be equipped with an apparatus at one tip that disperses light
propagating along the fiber in a uniform cylindrical pattern. This optical
radiating apparatus must produce a reasonably uniform pattern of light, so
the physician can have reasonable confidence in his applied dosage level.
The apparatus must also be able to transmit reasonably intense radiation
for effective treatment without developing "hot spots", optical, thermal
or mechanical damage. Finally, the apparatus must perform these tasks in
an environment in which it encounters blood, mucus, extraneous bits of
tissues, and other substances which may contaminate its optical
properties. Such an optical radiating apparatus for producing a uniform
cylindrical pattern of light, and a method for manufacturing such an
apparatus, is the subject of the present invention.
There have been a few other approaches to the problem of producing a
uniform cylindrical pattern of intense light around the tip of an optical
fiber. Work reported by Fujii et. al. in Optics and Laser Technology,
February 1984, p. 40-44, considers the scattering of light from the tip of
an optical fiber which has been subjected to various chemical etching and
roughening procedures. While the patterns of light are measured precisely,
they are far from uniform cylindrical patterns and not very useful in
practical treatments.
Another approach to producing approximately uniform cylindrical patterns of
light is that taken by the Quentron Optics Pty Ltd of Adelaide, Australia
in their optical fibers marketed under the trade designation "QF-IA" and
"QF-IV". The Quentron fiber has a light carrying core which is tapered to
a point, allowing the propogating light to escape at each point along the
tapered core. It is anticipated that the need to taper the core of the
optical fiber will add substantially to the cost and complexity of
manufacture.
The present invention comprises a coating for the tip of an optical fiber,
and method of producing the coated tip, which produces an approximately
uniform cylindrical pattern of light and requires no shaping of the fiber
core.
SUMMARY AND OBJECTS OF THE INVENTION
The present invention discloses an optical radiating apparatus constructed
on one end of a light-conducting optical fiber such that, upon
encountering this radiator, light is caused to leave the fiber and radiate
in a cylindrical pattern with respect to the central axis of the fiber.
This optical radiator is constructed such that the pattern of radiated
light is nearly a uniform cylindrical shape. Also the light is dispersed
around this cylindrical pattern in a nearly uniform intensity
distribution, without areas of light intensity significantly different
from the average distribution on the surface of the cylinder. The above
properties are achieved without the need to reshape the cylindrical core
of the optical fiber.
The present invention also discloses a method to manufacture the
above-described light radiating apparatus. For the intended use in cancer
treatment, significant light intensity must be carried by the optical
fiber and the radiating apparatus without developing "hot spots" and burn
regions, to the possible detriment of the patient. The radiating apparatus
must maintain its structural integrity and uniform cylindrical pattern of
radiated light in an environment of mucus, blood, tissue and other
substances encountered in the treatment of a patient.
Thus, a primary object of the present invention is to provide an apparatus
for producing a uniform cylindrical pattern of light at the tip of an
optical fiber.
Another object of the present invention is to provide a uniform optical
radiator as described, in a configuration suitable for use in patients.
Another object of the invention is to provide an optical radiator able to
disperse relatively intense radiation without suffering optical, thermal
or mechanical damage.
Another object of the present invention is to provide a method of
manufacturing the optical radiator with the properties described in a
reliable, and reproducible fashion, without the necessity of reshaping the
core of the optical fiber from its usual cylindrical shape.
DESCRIPTION OF DRAWINGS
FIG. 1: A perspective view of the optical radiating apparatus on the tip of
an optical fiber.
FIG. 2: Cross-sectional view of the optical radiating device as mounted on
the tip of an optical fiber, viewed as a section through the central axis
of the optical fiber (noted 2 in FIG. 1).
FIG. 3: Cut-away view of a patient's head with the present invention
inserted into the esophagus through a flexible tube.
DESCRIPTION OF PREFERRED EMBODIMENTS
FIG. 1 shows in perspective view a typical optical fiber, 1, conducting
light from the upper left portion of the figure into the region of an
optical radiating apparatus, 2. This radiating apparatus surrounds one
terminus of the optical fiber 1. The apparatus 2 is the subject of the
present invention. It disperses light propagating along optical fiber 1
into a uniform cylindrical pattern. Apparatus 2 is typically small enough
to insert into a patient, frequently through a tube into the esophagus or
bronchus, or into other regions of the body where approximately
cylindrical patterns of light are required. Another property required of
radiating apparatus 2 is that it withstand the relatively high intensities
of light it must carry. Typically, up to about 200 milliwatts per sq. cm.
of 630 nanometer radiation must be delivered to the tumor. Thus, the fiber
and the optical radiating apparatus should be able to withstand up to a
few watts of power without suffering significant optical, thermal or
mechanical damage even when used in vivo.
FIG. 2 shows in cross-sectional view the optical fiber terminating in
radiating apparatus 2. The light-carrying core of the fiber is shown as 3
in FIG. 2. The cladding region having a relatively low index of refraction
with respect to the core, 3, is shown as 4. The protective sheathing,
typically polyethylene or other plastic, is shown as 5. As shown in FIG.
2, the core region extends beyond the cladding and sheating, typically for
a distance of approximately 1.5 to 3 millimeters. The region surrounding
the exposed core, 6, is filled with light scattering material, 7. This
entire structure is then surrounded by a protective tubing 8, typically
polyethylene or glass. The length of the optical radiator is typically
approximately 2 cm in length and 1 mm in inner diameter. However, the
uniform cylindrical light scattering properties depend upon achieving the
correct balance of light leaving the fiber core 6, and being scattered by
the scattering region 7. Thus, there is no well-defined set of lengths for
the various regions, but ratios are more important. For other purposes,
optical radiators of much greater length can be fabricated by analogous
methods to those disclosed here. The distance from the upper end of the
radiating apparatus, 9, to the termination of the cladding and sheathing,
10, is typically twice as long as the distance from 10 to the termination
of the core, 11, which is approximately equal to the distance to the lower
terminus, 12, of the radiating apparatus. The region of scattering
material from 9 to 10 in FIG. 2 lies upstream from the exposed,
light-carrying core, 11. Thus, this region is not primarily contributing
to the light scattering properties of the apparatus, but serves to provide
better binding of the scattering material, 7, to the optical fiber, 1. The
primary light dissipating portion of region 7 lies in the region from 10
to 12 in FIG. 2.
In order to achieve a uniform cylindrical pattern of light around the
circumference of the cylinder, it is necessary that the scattering power
of the scatterer 7 increase along the length of the scattering region from
10 to 12 in FIG. 2. The amount of light dispersed away from the central
optical axis of the core is proportional to the incident light intensity.
The constant of proportionality is referred to as the "scattering power."
As light is lost from the incident propagating beam into the outer
portions of the cylinder, less incident light is available "downstream".
Thus, to maintain a constant scattered light intensity, the scattering
power must increase in region 7 as one scans from edge 10 to edge 12. To
make a truly uniform cylindrical pattern, the scattering power must
increase logarithmically.
FIG. 3 illustrates how the present invention would be used in treatment of
cancer of the esophagous. The optical fiber 1 is typically passed through
a flexible tube, 13, such that the optical radiating apparatus 2 is in the
region of the tumor. Laser light is introduced into the end of the fiber
opposite apparatus 2 at a location remote from the patient. Light is then
radiated into the desired cylindrical pattern, 14, to effect the
treatment.
It is critical to the proper functioning of the apparatus that the optical
scattering region be free of air bubbles or other impurities which would
tend to cause preferential absorption of the light and, hence, damage to
the material. Another critical aspect is the method of coating the optical
scattering material, 7, around the tip of the fiber to achieve a resonably
uniform cylindrical pattern of scattered light. Without a uniform pattern
of light, the physician cannot reliably provide the proper dosages to the
entire treated area. Thus, another part of the present invention concerns
the method of manufacturing this optical radiating apparatus.
A standard optical fiber suitable for transmitting red light (630 nm) is
stripped by usual stripping methods exposing at one end thereof a length
of core well in excess of the required 1.5 mm to 3 mm. The exposed length
of core is carefully cleaved to the desired length of approximately 1.5 to
3 mm. The tip of the cleaved core is polished flat using, typically,
cerium oxide polishing compound although polishing directly with a
suitable polishing cloth may also be used.
Having an optical fiber with a short length of exposed, polished core, the
scattering region is constructed to produce the desired uniform
cylindrical scattering pattern. A typical scattering medium, which gives
preferred performance in this invention, is composed of approximately
equal parts powdered quartz (crystobolite) and an optical adhesive. Any of
several optical adhesives manufactured by the Norland Company have been
tested and found to give good performance.
A critical aspect of the manufacturing process is to apply the scattering
medium such that increasing scattering is produced towards the termination
of the optical radiator. One useful way to accomplish this is to propagate
visible light down the optical fiber during the fabrication process. This
light is typically red laser light from a HeNe laser, launched into fiber
from the opposite end from that upon which the optical radiator is being
constructed. This light must have suitable intensity to be easily visible
to the technician carrying out the fabrication procedure.
Using this test illumination, the technician applies (typically by dipping)
the tip of the fiber into the scattering medium. The polished tip of the
core region is cleaned of scattering medium upon removal from the dipping
vessel. It is important in the fabrication procedure that the polished tip
of the core remain free of scattering medium until the final fabrication
step.
The applied scattering medium is inspected visually by the technician for
bright spots or other non-uniformities in the scattering pattern from the
test light. Any such imperfections are manually smoothed by the technician
before curing. The scattering medium, typically being a mixture of curable
optical adhesive and quartz powder, is then cured by exposure to
ultraviolet light from a standard source, typically as recommended by the
adhesive manufacturer. Further layers of scattering medium are applied,
inspected, smoothed and cured as described above until the desired light
scattering pattern is obtained.
The final manufacturing step involves inserting the fiber, with its
coatings of scattering medium, into a tube, typically plastic (such as
polyethylene) or glass. The spaces remaining in the interior of the tubing
are carefully filled with scattering medium. This is typically
accomplished by inserting, via hypodermic syringe, a small amount of
scattering medium into the tubing before the optical fiber and radiating
assembly are inserted into the tubing. Care must be exercised to leave no
air bubbles or other foreign substances that can cause "hot spots" or
otherwise lead to optical, thermal or mechanical damage. The final curing
is performed, the tubing is cut to the desired length, and the fiber with
its appended optical radiating apparatus is ready for use. We note in
passing that the tubing 8 in FIG. 2 is shown co-terminus with the
scattering medium 7. This is not critical to the practice of the present
invention, but it is frequently advantageous in practice (to facilitate
insertion through a bronchoscope, for example) to leave excess tubing 8,
cut at an angle other than perpendicular to the optical fiber axis, 2 in
FIG. 1, to act as the leading edge in inserting the device into the proper
area for treatment. Such minor modifications are standard techniques well
known in the art.
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