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OCR for page 101
Lasers in Medicine
Rodney Perkins, M.D.
In nature, periodic mutation creates new life-forms and moves
the species to new levels of performance and being. Similarly,
from time to time in human endeavors, mutative cerebration
provides important new concepts that we can then refine and
develop into processes that we hope will enrich the human
, . .
condition.
The laser is such a type of contribution. Its impact is already
widespread in science, communication, industry, and medicine.
This impact will grow rapidly as we better understand its nature,
develop permutations, and integrate both basic and advanced
forms closely with other core technologies to produce hybrids
that can satisfy as yet unknown needs.
The use of the laser in medicine and surgery has a relatively
short pedigree of less than two decades. Although the range of
laser radiation extends both below and above the visible portion
of the electromagnetic spectrum, that radiation is, in a sense,
only a special form of light. The use of other forms of light in
medicine has a longer history. There is documentation that the
ancient Egyptians recognized and used the therapeutic power of
light as long as 6,000 years ago (Figure 1~. Patches of depigmen-
ted skin, now referred- to as vitiligo, were cosmetically undesir-
able. Egyptian healers reportedly crushed a plant similar to
presentday parsley and rubbed the affected areas with the
crushed leaves. Exposure to the sun's radiation produced a
severe form of sunburn only in the treated areas. The erythema
LIGHT IN MEDICINE
101
OCR for page 102
~ 02 RODNEY PERKINS, M.D.
1 1
FIGURE 1 The ancient
Egyptians recognized many
beneficial qualities of solar
radiation. Photograph by
Glenn Calderhead.
subsided, leaving hyperpigmentation in the previously depig-
mented areas.
In Europe in the late eighteenth and early nineteenth centu-
ries, at the height of the Industrial Revolution, a myriad of
factories and industrial plants spewed smoke into the atmo-
sphere, filtering out many of the beneficial components of the
sun's rays. Deprivation of ultraviolet radiation contributed to
calcium deficiency in the main skeletal bones, leading to the
characteristic deformity known as rickets. The much more
insidious and fatal pulmonary tuberculosis was also prevalent. It
was found that sunlight helped alleviate the symptoms of these
diseases, and so sanitariums sprang up all over Europe, espe-
cially in Great Britain and Switzerland. They were usually
located on higher ground or by the sea, because this seemed to
increase the efficacy of the therapy. We now know that pure
air filters out fewer of the beneficial components of solar radia-
t~on.
In the late nineteenth century, the Danish scientist Nils Finsen
used a quartz-and-water cooling system to extract the ultraviolet
from both solar and man-made arc-lamp radiation to treat
various skin conditions, such as vitiligo and psoriasis, a scaly
overproduction in areas of skin. The significance of Finsen's
OCR for page 103
LASERS IN MEDICINE 103
work was that, for the first time, an artificial light source was
being used therapeutically.
Sixty years later, only a quarter of a century ago, a light source
more powerful than the sun was developed by Theodore H.
Maiman at the Hughes Research Laboratories in Malibu, Cali-
fornia, heralding a new era in phototherapy. Maiman's laser
used a ruby crystal to produce its intense deep red beam. Other
lasers using different media soon emerged. In 1960, Ali tavan
created the helium-neon gas laser, first emitting in the infrared
part of the spectrum and a year later in the important red line.
A year later Peter A. Franken demonstrated that certain crys-
talline materials could effectively double the frequency of an
incident beam. The year 1964 was a prolific year for laser
development and yielded an outstanding harvest of lasers used
in clinical medicine. C. Kumar N. Patel introduced the carbon
dioxide (CO2) gas laser, which produced an invisible beam in the
far infrared. Another invisible laser in the near infrared, the
neodymium yttrium-aluminum garnet (Nd:YAG) was contrib-
uted by Guesic, Marcos, and Van Uitert. The argon gas laser
emitting in the visible blue-green spectrum was demonstrated by
William Bridges. Since then, literally thousands of substances
have been used to produce laser energy.
However, those first few that appeared so close together, in
general, have remained until today the most popularly used
lasers in clinical medicine and surgery (Plate 41. Maiman's ruby
laser, although still occasionally used in some dermatological
applications, is no longer in common medical use. The helium-
neon laser is mainly used as an aiming beam for the invisible
infrared CO2 and Nd:YAG lasers. The argon laser is used
extensively in ophthalmology and dermatology and less so in
orology, neurosurgery, urology, and gynecology. Both infrared
lasers, the Nd:YAG and particularly the CO2, have found a
variety of clinical applications. The CO2 laser has been used to
vaporize tissue in almost every specialty, whereas the Nd:YAG
laser has been used primarily for tissue coagulation in gastroen-
terology and urology. A specialized short-pulse, high peak
power Nd:YAG laser has been used effectively in ophthalmol-
ogy after cataract surgery.
Frequency-doubled lasers were used only experimentally until
a higher power laser was made possible by using doubling
crystals of potassium titanyl phosphate (KTP) developed by J.
Bierlein at Du Font. The laser that resulted from doubling the
Nd:YAG with KTP—called the KTP/532 laser began clinical
use in 1983 and is now being applied in a wide variety of surgical
. .
specla. ales.
OCR for page 104
~ 04 RODN BY PERK NS, M. D.
MINIMALLY INVASIVE
SURGERY
11
Why is the laser used in medicine, and why is its use increasing?
Some answers can be found by looking at a few of the universal
changes occurring in medicine. Economic, political, and socio-
logical factors in our society frequently affect the disposition of
scientific discovery, just as scientific and technological progress
influences broad changes in the nontechnical spheres of human
activity. These factors are Newtonian in the sense that actions in
one sphere of activity have a direct influence on actions in other
spheres.
In the past decade, there has been a growing trend toward a
less invasive style of surgical intervention. This style is charac-
terized by achieving a maximal treatment effect with minimal
damage to surrounding and overlying normal structures and is
termed minimally invasive surgery, or MIS.
The trend toward MIS is being driven by a multiplicity of
factors. High-technology diagnostic devices, such as computer-
ized axial tomography, magnetic resonance imaging, as well as
sophisticated optical devices in the form of flexible fiber-optic
endoscopes and intravascular catheters, have enhanced our
ability to identify disease processes early and locate them accu-
rately. Generally, the earlier a tumor or growth can be identi-
fied, the more responsive it is to therapy by a minimally invasive
technique.
Human psychology is also part of this changing equation.
Everyone has an inborn fear of standard invasive surgical
procedures. Given an equivalent surgical outcome, we will
almost always choose a less invasive procedure. The increase in
patient consumerism, coupled with rapid and widespread trans-
mission of information on new MIS procedures through video
and popular print media, also fuels this trend.
Economics exerts a strong influence on the trend toward MIS.
These procedures are cost-effective to insurers, corporations,
and the government, since most are done on an outpatient basis.
This results in reduced cost, lower morbidity, and less time away
from work. Even when MIS techniques are used as an adjunct to
more invasive surgical approaches, reduced destruction of tissue
frequently leads to quicker recovery with a shortened, lower cost
hospitalization.
The laser is an integral part of this trend toward MIS. It is well
suited to MIS because it can create precision surgical effects at a
distance. Laser energy can be transmitted through endoscopic
devices passed through the body's natural orifices, or it-can be
OCR for page 105
LASERS IN MEDICINE ]05
delivered through transdermal probes that require minimal
incisions of 1 cm or less. This is particularly true for those wave-
lengths transmissible through quartz fiber-optic waveguides.
Controlled tissue effects can also be delivered noninvasively.
This is commonly done in the treatment of intraocular condi-
tions and intradermal lesions by wavelengths characterized by
high transmissiveness through the ocular and dermal media.
The laser is a very effective tool for the surgeon who under-
stands its advantages and limitations. The surgeon's knowledge
of laser science need not be as detailed as that of the physicist but
should include a general understanding of principles of light
transmission, reflection, scatter, and absorption. An under-
standing of the interaction of the various wavelengths in tissue
components with widely differing coefficients of absorption
provides the primary basis for safe and effective surgical appli-
cation of this new technology.
The biological effect of lasers is a function of three elements:
laser wavelength, energy density, and tissue absorption (Figure
21. For the surgeon, it is helpful to look upon wavelengths as the
nature or character of the surgical instrument and upon energy
density as the "dosage." The coefficient of absorption of the
target tissue might be thought of as a sponge for this therapeutic
light, but is more difficult to characterize and simplify.
Two important constituents of tissue absorption are pigment
and water. In all but the most specialized of tissues there is
generally a vascular supply rich in hemoglobin pigment. Other
chromophore pigments, such as melanin in skin and myoglobin
in muscle, are prevalent. All tissues contain water. Visible light
from argon and KTP/532 lasers is well absorbed in hemoglobin,
whereas infrared radiation from Nd:YAG lasers is poorly ab-
sorbed. In water, CO2 laser radiation is almost totally absorbed,
whereas the visible wavelengths and Nd:YAG laser radiation
have little absorption. Thus, each of the surgical laser wave-
lengths has advantages and disadvantages depending upon the
target tissue and the surgical effect desired.
It is not completely accurate to generalize about the relative
amounts of penetration and scatter of these surgical lasers in
tissue, because that is a function of wavelength and the specific
absorption characteristics of individual tissues. However, if we
consider a hypothetical nominal soft tissue with a mixture of
tissue types found in the body, we can compare the general
BIOLOGICAL
EFFECTS
1 1
OCR for page 106
~ 06 RODNEY PERKINS, M.D.
FIGURE 2 The biological effect of lasers is a function of three main
factors.
scatter of these various wavelengths. In this hypothetical model,
we would find CO2 laser radiation absorbed on the surface with
little forward scatter. The wavelengths of the Nd:YAG laser
would have poor surface absorption and would scatter deeply
into the tissue. The visible wavelengths would have forward
scatter somewhat greater than the CO2 laser wavelengths but
significantly less than those of the Nd:YAG laser.
The thermal patterns in this conceptual model are also varied.
The CO2 laser produces a surface hot spot that creates a thermal
front that conducts heat into the tissue. The thermal center
produced by the Nd:YAG laser is actually beneath the surface of
the target tissue, thus making it difficult for the surgeon to judge
the ultimate surgical effect. The visible wavelengths have some of
the surface heat effect of the CO2 laser, especially once surface
vaporization and some penetration into the tissue is initiated.
The CO2 laser is an efficient vaporizer of tissue. The Nd:YAG
laser does not characteristically vaporize tissue unless power
densities are relatively high, but rather, it creates a coagulative
necrosis within the tissue. The argon and KTP/532 lasers
vaporize tissue effectively, especially after the process has been
initiated. It is possible that as the target tissue begins to vaporize,
a blanket of microscopic char particles is created on the surface
and acts as a chromophore, catalyzing the surface absorption of
the next quantum of visible laser light. The visible wavelength
lasers are also good hemostatic coagulators. This quality proba-
OCR for page 107
LASERS IN MEDICINE ]07
bly derives from the slight scatter, which is absorbed in the
hemoglobin within the capillaries and small vessels, thus creat-
ing intravascular coagulation. Carbon dioxide lasers have less
hemostatic effect. This effect results primarily from the advanc-
ing thermal front, not because of any specific intravascular
absorption of the wavelength. Whether the laser radiation is
visible or invisible, the phenomenon that causes the surgical
effect is the absorption of radiant energy and its conversion into
heat in the target tissue.
The amount of heat generated determines the alteration of
the tissue. At approximately 50°C-60°C, denaturation begins to
occur in collagen and other proteins. At 65°C and above,
denaturation proceeds to extensive physical changes, including
coagulation. At 80°C-85°C, blood vessels shrink. This effect is
probably due to the alteration of the collagen within their walls
and is a component of the hemostatic effect of lasers. lust below
100°C small vacuoles are sometimes formed in the tissue as the
slightly pressurized intra- and extracellular water begins to boil.
Surface vaporization takes place at 100°C, and much of the
particulate matter of the tissue leaves the surface with the
emitting vapor. At several hundred degrees Celsius, the remain-
ing organic materials revert to their basic carboniferous form
and charring occurs.
An understanding of these interactions between temperature
and tissue is important to the surgeon in achieving three main
surgical effects: coagulating, vaporizing, and cutting. In prac-
tice, the thermal boundaries between these effects are not as
controllable as they are in a laboratory setting or theoretical
contemplation, but the surgeon can achieve a predominant
surgical effect by manipulating the one variable in the triad of
the biological effect equation subject to change intraoperatively.
Currently, lacking a variable-wavelength laser, the surgeon has a
fixed frequency available and generally a fixed tissue coefficient
of absorption as well. The only manipulable variable of the triad
. ~ .
Is energy density.
Coagulation for hemostasis is best effected by using a lower
energy density, which is achieved by enlarging the spot size or
lowering the absolute power or exposure duration. The surgeon
can use this technique, particularly with the visible wavelength
lasers and the Nd:YAG laser, for prophylactic hemocoagulation to
prevent bleeding in small vessels and vascularized target tissue and
to control small vessel hemorrhage if it occurs (Figure 31.
Vaporization is used to remove tissue mass primarily in tumor
SURGICAL EFFECTS
ll
TV.
OCR for page 108
~ 08 RODNEY PERKINS, M.D.
1 1
FIGURE 3 Coagulating to achieve hemostasis.
excision. The optimum beam conditions are a large spot size and
high power density to achieve a higher rate of tissue removal
(Figure 4~. However, where precision is important because of
vital adjacent structures, a high rate of removal may be unde-
sirable for the preservation of those structures.
Cutting with the laser is basically a thin linear vaporization
produced by combining a high power density with as small a
- 3 ~3 - -~3~3~-~-~ -4 ~-~-~33~3~ ~~-~ -A
FIGURE 4 Vaporization for removal of a tissue mass.
OCR for page 109
LASERS IN MEDICINE ]09
. . . ~. it S . ~ ~ .- .
·- S ^ . .~ .. T: ~
':
FIGURE 5 Cutting for incision.
........
.
spot size as possible. In a way, cutting with a laser is analogous to
cutting with a scalpel, which produces a high pressure density.
Efficient cutting is achieved by moving the beam at a rate that
produces the desired cut, yet that minimizes secondary thermal
effects in the adjacent tissue (Figure 5~.
The surgeon has various instruments available for cutting and
must select the one most appropriate to the task and the tissue.
The only advantage to cutting with the lasers now in use is the
degree of hemostasis that accompanies a laser cut and the ability
to cut in areas difficult to reach with conventional instruments.
Although the evidence is anecdotal, some surgeons report that
patients say they have less postoperative pain when tissue is
excised with the laser.
Safety and precision are maximized when pulses (for exam-
ple, 100 ms) are used, since the damage caused by an off-target
beam can be limited. The least safe use of a laser in surgery is the
continuous beam, which, if it is off course, can significantly
damage nontarget tissues before the surgeon can take corrective
action. Between these extremes is the use of a train of pulses
with a beam-free interval (for example, 100 ms on and 500 ms
off). Such parameters allow the surgeon to view the effect of
each pulse and aim the beam during the off interval or cancel
the next pulse should problems arise.
Coagulating, cutting, and vaporizing are generic surgical
effects achieved throughout a procedure by manipulating the
beam parameters. When combined with an understanding of
1
111
OCR for page 110
~ ~ 0 RODNEY PERKINS, M.D.
CLINICAL
APPLICATIONS
1
1
the anatomy of the area and the desired therapeutic surgical
alteration, the surgeon has an effective new tool that can help
enhance the quality and duration of life.
Surgeons of all specialties can use lasers for coagulating, vapor-
izing, and cutting. However, in each medical specialty, there are
certain lesions and conditions for which the laser is more
commonly employed. The applications described below are not
the only uses of lasers in these specialties, but they reflect the
predominant current uses.
OPHTHALMOlOGY
Ophthalmology is the surgical specialty that is the most mature
in using the laser as a therapeutic modality. In the late 1960s,
pioneering ophthalmologists first applied the ruby and then the
argon laser to prevent and control bleeding from retinal vessels.
The visible wavelengths are well suited to this task, since they
pass through the cornea, lens, and fluids of the interior of the
eye with little absorption until they encounter the hemoglobin
pigment within the retinal vessels or the pigment in a layer
adjacent to these vessels. Here, the energy of the laser beam is
absorbed, creating heat that coagulates the vessels.
Control of vascular elements in the retina through laser treat-
ment has preserved vision in thousands of patients with pro-
liferative diabetic retinopathy and senile macular degeneration.
This latter condition is the most frequent cause of blindness in
people over 65 years of age. The argon laser is also used to create
"spot welds" to reattach or prevent the inner neurosensory portion
of the retina from separating from the outer pigmented layer in
retinal tears and the early stages of retinal detachment.
Glaucoma is a common condition that causes visual impair-
ment. In this disorder, the normal outflow of fluids within the
eye is decreased by malfunction of the filtering mechanism. The
ensuing increase in pressure damages the optic nerve. The laser
is used to treat these delicate filtering elements near the outer
perimeter of the iris. Improvement in filtering with resultant
reduction in intraocular pressure occurs in many cases, aiding in
the control of this serious disorder.
In some patients, a visual problem persists after removal of
cataracts because of opacities in the remaining lens suspension
capsule. Short, high-peak power pulses (5-10 us, about 1 mJ per
OCR for page 111
LASERS IN MEDICINE 111
pulse) from a specialized Nd:YAG laser are beamed into the
opacified membrane. The beam creates a plasma that disrupts
the membrane, thus clearing the visual pathway.
In experimental work now under way, lasers are being ap-
plied to refractive problems of the cornea. Excimer (gas) lasers
are being used to make precise cuts in various patterns outside
the visual axis of the cornea. As these cuts heal, the curvature of
the cornea is altered and vision is affected. Another exciting and
even more experimental concept is laser corneal sculpting.
Using an excimer laser combined with a computer-controlled
x,y,z plane delivery system, the refractive power of the cornea is
modified by changing its outer curvature. The safety and
efficacy of this concept are not proved. Two potentially serious
impediments are possible mutagenic effects of the ultraviolet
light and clear regeneration of the protective surface epithelium
of the cornea.
The excimer cuts are not thermally derived, as is the case in
other currently used surgical lasers. When examined histologi-
cally, the edges of an excimer cut show virtually no evidence of
thermal damage. This "cold cutting" is thought to be due to
disruption of molecular bonds. If shown to be successful, it
would have other surgical applications.
DERMA TOlOGY
The argon and CO2 lasers have been used for years to treat
various skin conditions. More recently, the KTP/532 laser has
also been shown to be effective for these disorders.
The visible wavelengths work particularly well in the treat-
ment of skin lesions that involve vascular abnormalities and in
the removal of tattoos. The standard application is in congenital
hemangiomas, which are purplish red discolorations of the skin
referred to as "port wine" stains. They are basically abnormal
aggregations of capillaries and small vessels in the dermis of the
skin. Before the existence of the laser, little effective treatment
existed for this condition. A lower power (1-2 W) argon or
KTP/532 laser is beamed onto the lesion. These wavelengths
pass through the relatively translucent epidermis of the skin and
are absorbed in the hemoglobin inside the hemangioma network
coagulating the vessel. Initially, the elimination of these vessels
gives a pallorous appearance, but later, new vessels grow into the
area and give it a more normal color.
The artificial skin pigments that result from tattooing are
removed in a similar manner. Surgeons in many specialties use
the CO2 laser to vaporize and remove various raised skin lesions.
OCR for page 112
2 RODN EY PERK! NS, M. D.
OTOLARYNGOlOGY: HEAD AND NECK SURGERY
The CO2 laser has been used in the treatment of laryngeal
lesions since the early 1970s. Although the throat is accessible
with conventional instruments, it is difficult to work deep within
the throat with long instruments. Lasers are used to vaporize
vocal cord polyps and other benign lesions, but they are not
generally used as a primary treatment approach for obviously
malignant growths.
The KTP/532 laser has recently been used effectively in
laryngeal lesions. Besides producing a very hemostatic vaporiza-
tion, its smaller beam spot size is advantageous in making precise
. .
exclslona ~ cuts.
Like sight, hearing also has benefited from laser technology.
The argon and KTP/532 lasers are used successfully in the
treatment of the hearing impairment associated with otosclerosis
of the stapes. The stapes, or "stirrup," is the smallest and
innermost of the three bones, or ossicles, that transmit sound
vibration from the eardrum to the fluids of the inner ear (Plates
5 and 61. Otosclerosis is a benign bony growth that sometimes
develops adjacent to the stapes, causing its fixation (Plate 7~.
With local anesthesia, under a stereomicroscope, the eardrum is
folded out of its normal position so that the laser can be beamed
through the normal ear canal onto the stapes (Plates 8 and 9~.
The arches of the stapes are vaporized, and the outer portion of
the stapes is removed (Plates 10 and 1 11. Using 100-ms pulses of
1-2 W and a spot size of about 250 ,um, a rosette pattern of small
holes is vaporized in the stapes footplate with an aggregate
diameter of 0.6-0.8 mm (Plates 12 and 131. One end of a piston-
shaped prosthesis is placed into the opening, contacting the
inner ear fluids, and the other is attached to the adjacent ossicle,
thus reestablishing the vibratory pathway (Plates 14 and 15~.
This virtually vibrationless entry has several advantages over a
manual technique: precision, reduced vibratory trauma to the
exquisitely sensitive inner ear, and minimal morbidity, which is
due to reduced vibratory stimulation of the nearby balance
sensors. The procedure is routinely done on an outpatient basis,
. . .
wit n concomitant savings.
GASTROENTEROLOGY
The hemostatic effect of the Nd:YAG and argon lasers has been
used to control bleeding from gastric ulcers. However, this
application is being superceded by a less expensive resistance
heater probe employed in a similar manner through a fiber-
optic gastroscope. The Nd:YAG laser is also used to necrose
. _ _
OCR for page 113
LASERS IN MEDICINE 113
obstructive lesions of the esophagus in cancer palliation. Polyps
and tumors of the colon in the lower gastrointestinal tract can
also be treated with lasers.
NEUROSURGERY
In neurosurgery, the laser has been used primarily to vaporize
solid tumors. The CO2 infrared laser has been used predomi-
nantly, but visible wavelengths are used increasingly because of
their superior hemostatic properties, precision, and ease of
delivery.
Both visible and infrared wavelengths offer increased preci-
sion of removal, as well as reduced bleeding and traction on
neural structures. These factors reduce patient morbidity and
possibly also lower the incidence of certain potential complica-
tions. Argon and CO2 lasers have been used to reduce intracta-
ble pain in some paraplegics by making precise destructive
lesions in the area of the spinal cord that receives the roots of
. . . ~
pa~n-sens~t~ve nerve h Jers.
GYNECOLOGY
At present, the field of medicine that is growing most rapidly in
its application of the laser is gynecology. For many years the CO2
laser has been used to vaporize areas of the uterine cervix that
evidence a premalignant state. This laser procedure results in
reduced bleeding and faster healing than other techniques.
More recently, minimally invasive intra-abdominal surgery
has been possible by combining the laser with endoscopic
Instrumentation. The best example of this is the treatment of
endometriosis, a condition in which tissue that normally lines the
uterus is found ectopically in the lining of the interior of the
pelvic abdominal cavity. At the time of monthly menses, this
tissue swells and hemorrhages in a manner similar to that of the
normally located endometrium of the uterus. Consequences of
this condition include pain and infertility.
In laser treatment for endometriosis, a 1-cm incision is made in
the abdominal wall, a tube-shaped viewing laparoscope is inserted,
and the patches of endometriosis are identified. A 600-,um fiber-
optic waveguide lying in a channel within the laparoscope is used to
deliver the vaporizing beam to the target lesions.
This laser treatment of endometriosis is one of the best
examples of minimally invasive surgery. Instead of requiring a
standard wide abdominal incision, an effective treatment is
accomplished with minimal effect on healthy tissue, virtually no
blood loss, markedly reduced pain and discomfort, shorter
.
OCR for page 114
114 RODNEY PERKINS, M.D.
hospitalization, earlier return to personal productivity, and
lower cost.
GENERAL SURGERY
Laser applications in general surgery have not been developed
to the same degree as in other specialties. Some general sur-
geons make skin incisions with the laser, but this is rarely done.
Using vaporization in combination with more traditional tech-
niques when removing large tumors is probably the most com-
mon use of lasers in general surgery.
This limited use probably derives from the nature of the
lesions that the general surgeon encounters. These lesions are
usually gross tumors or conditions that require anatomical
reconstruction. Also, the surgical site is usually reasonably well
accessed once entry through the incision is accomplished. Such
problems do not lend themselves as well to minimally invasive
and precision techniques the areas in which lasers have the
most advantage over standard surgical approaches.
PUlMONOLOGY
Obstructive mass lesions of the lower airway in the trachea and
the bronchial tree are treatable with laser surgery. Through a
bronchoscope inserted through the mouth and throat, these
lesions can be removed hemostatically, restoring the airway.
This practice is used for benign growths and for palliative, but
not primary, treatment of malignant neoplasms.
UROLOGY
Clinical application and investigational use of lasers in several
urological conditions represent another outstanding example of
minimally invasive surgery and the expanding impact of this
technology. Bladder tumors that have not penetrated beyond
the musculature of the bladder wall are treated with a minimally
invasive technique through the natural urinary orifice. A view-
ing cystoscope is inserted through the urethral opening into the
fluid-filled bladder, where the lesion is identified and removed.
The Nd:YAG, argon, and KTP/532 lasers have been used
successfully in this procedure.
All three wavelengths pass efficiently through the infused
irrigating fluid. The Nd:YAG laser radiation penetrates and
coagulates the lesion, which later sloughs off, and the radiation
from argon and KTP/532 lasers vaporizes the mass. Higher
1 1
OCR for page 115
LASERS IN MEDICINE ~ 1 5
energy densities are required for vaporization in this fluid
milieu than in air because of heat transfer into the irrigant.
Laser treatment of these lesions can be done under local
anesthesia with the patient awake, whereas ablation with elec-
trosurgical units is performed with the patient under general
anesthesia because of attendant pain. This makes use of the laser
particularly advantageous for the elderly, for whom other
medical problems may make general anesthesia undesirable.
Urethral strictures that are soft tissue obstructions that im-
pede the flow of urine from the bladder can be vaporized with
an argon or KTP/532 laser wavelength. Small urethral stones
have been broken up by a fiber-optically delivered short pulse ( 1
ms, 10-100 mi) from a pulsed dye laser emitting in the green-
yellow spectrum. This application is still being studied for safety
and efficacy but is another potentially exciting and beneficial
laser application in urology.
ORTHOPEDIC SURGERY
Lasers have been used clinically very little in orthopedic surgery.
Orthopedic surgeons deal primarily with alterations of bone,
cartilage, and ligaments. Currently used surgical lasers do not
cut bone as well as other electrical and mechanical instru-
ments. Although it is possible to cut bone with surgical lasers,
they produce significant undesirable adjacent thermal destruc-
tion.
Investigators are now studying the technique of delivering
lasers to the interior of the knee through an arthroscope that is
inserted through a small puncture incision in the skin. This may
prove a useful method for removing damaged cartilage.
CARDIOVASCULAR APPLICATIONS
The lure of using lasers in pursuit of the nation's number-one
cause of death is strong, and many research efforts are under
way in this area. Using an intravascular viewing catheter that
holds a fiber-optic waveguide to approach and destroy an
obstructive coronary artery lesion is an exciting concept the
stuff that dreams are made of. Whether this is feasible by using
a laser remains to be seen. A technique to eliminate intravascular
lesions will be developed, but whether it will be laser based,
electrical, mechanical, or some other combination of techniques
is not clear. Several problems confound this development.
Obstructive lesions are neither simple nor uniform. They may
consist of a fresh clot; soft, multicolored atheromata; a hard,
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6 RODNEY PERK NS, M. D.
calcified plaque; or a combination of these. The obstruction is
irregular, and the restricted vessel lumen, if still present, is
usually eccentric.
The highly varied color and consistency of soft atheromata
and arteriosclerotic plaque make it harder to predict a consistent
effect of a laser. Undesirable thermal damage to vessel walls may
cause subsequent vessel constriction, aneurysm, or perforation.
At the same time, adverse thermal effects on the myocardial
electrical conduction system must be considered. Investigators
are also studying the question of whether the solid by-products
of ablation could block vessels. All of these problems pose
potential difficulties.
Argon lasers are being used investigationally in attempts to
vaporize obstructive lesions directly and to heat probe tips.
Excimer lasers are being studied for use in plaque removal, but
use of certain ultraviolet wavelengths is encumbered by delivery
problems and the longer term mutagenic potential. Other
wavelengths are undoubtedly undergoing evaluation for these
purposes. Should these developments succeed, there will be a
certain irony that a modality used first for its ability to close
vessels should also be successful in opening them.
Additional experimental work is being done to treat certain
arrhythmias by precision photoablation of areas of the conduc-
tive systems and to remove from heart valves any unwanted
tissue that prevents them from closing adequately. The success-
ful wedding of lasers with the recently developed intra-arterial
catheter technology in cardiovascular applications could help
considerably in mitigating the effects of one of our largest health
care problems.
PHOTODYNAMIC THERAPY
The photoactivation of certain chemicals in viva has potential in
the treatment of cancer. A dye material called hematoporphyrin
derivative (HPD) is being activated by exposure to low-energy
laser radiation with beneficial effects on certain malignant neo-
plasms.
Given to the patient about 48 hours ahead of the anticipated
laser exposure, the HPD becomes intimately associated with
malignant cells. Upon photoactivation of the HPD, a photo-
chemical reaction causes the death of the malignant cell hosting
the HPD but does not kill adjacent normal cells.
Both 630- and 532-nm wavelengths are effective in activating
HPD. The red 630-nm light penetrates farther into most tissues
than the green 532-nm wavelength. However, 532-nm photo-
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LASERS IN MEDICINE ~ ~ 7
activation may be useful in bladder tumors, where the lesions
are superficial and usually multicentric and can be exposed to
the photoactivator wavelength delivered by a fiber-optic wave-
guide with a diffusion tip.
The development of other photoactive entities specific to
different cancers might add new possibilities for the treatment
of malignancies.
At present, lasers have contributed significantly to the treatment
of a wide variety of maladies. These applications and today's
clinical lasers represent only the infancy of phototherapeutics.
We will see other lasers evolve and take their places at the center
of the clinical stage. Ultraviolet, diode, and free electron lasers
all hold promise. Combinations of wavelengths, distributed both
spatially and temporally, may provide tissue and surgical effects
superior to those of single wavelengths. Miniaturization will
enhance their usefulness.
Instrumentation derived from combinations of photoelectro-
nics and other core technologies will produce still more alterna-
tives to standard surgical approaches. Exotic and more highly
specialized delivery devices will expand the surgeon's ability to
achieve precision therapy with low morbidity.
Ultimately, these endeavors will advance minimally invasive
surgery beyond our dreams. However, this achievement will be
the product of human creativity and cooperation. The future of
phototherapeutics will not be created by physicists, engineers, or
surgeons alone but will become a reality only through the
collective human resources of science, medicine, finance, and
government working together with vision.
TH E FUTU RE
Representative terms from entire chapter:
laser radiation
