Laser interstitial thermal therapy
Encyclopedia
Laser interstitial thermal therapy (LITT, also referred to as laser-induced interstitial thermotherapy or laser-induced thermotherapy or interstitial laser therapy) is a surgical procedure in which destruction of soft tissues in the body is effected through high temperatures generated by the local absorption of laser energy. LITT is also sometimes referred to as laser ablation
or laser thermal ablation, but this terminology is inaccurate since the goal of LITT is to destroy tissue through thermal coagulation and thermal necrosis rather than by removal (ablation).
wavelength range (from about 700 - 2000 nm), though when appropriate
chromophores are available, visible wavelengths (e.g. green) can also be
used. Photons launched into tissue meet one of three fates: scattering
,
absorption
, or exit from the tissue. When photons are absorbed, the energy from the photon is converted into inter- and intra-molecular
energy and results in generation of heat within the tissue.
At the same time the good absorption in tissue limits the size of the lesion created by the laser irradiation. So a compromise between good penetration and good absorption has to be found. After initial absorption the temperature generated spreads through the tissue and enlarges the lesion somewhat, dependent on the perfusion of the tissue. Large vessels will transport the heat away from the site and the effective temperature achieved is reduced.
As heating continues and tissue temperature is elevated, several processes occur which
lead to the destruction or death of the tissue:
At temperatures of 100 degrees Celsius or more, water in the tissue and in
the intracellular compartments may vaporize and lead to rupture or
explosion of cells or tissue components.
At temperatures above 60 degrees Celsius, proteins and cellular components of the tissue become severely denatured and coagulate leading to cell and tissue death.
At somewhat lower temperatures, generally above 45 degrees Celsius, prolonged
exposure leads to the thermal denaturation of non-stabilized proteins such
as enzymes. Though cell death is not immediate, destruction of critical
enzymes leads eventually to cell death.
Optical absorption in the near-infrared range is generally due to
combination aniuuud overtone bands of fundamental molecular stretches. For
wavelengths near 1000 nm, water is a primary absorber of optical energy.
was invented at Bell labs and first described in a paper
in 1958. A ruby laser as first constructed in 1960, and by the mid-1960s
medical applications were beginning to be explored. One of the first
publications of what was called laser endoscopy (which could essentially
be called LITT) was by S.G. Brown in 1968.
Medical laser applications grew somewhat steadily throughout the 1970s, but
in the 1980s exploded as new laser technologies and new and cheaper fiber
optics became available. After an initial boom, lasers generally settled into
a few niche areas in surgery and medicine.
In the 1990s, availability of new high-power and compact semiconductor
(diode) lasers increased the convenience of laser surgery, in particular
LITT. Since the early 1990s a number of surgical applications and investigations
of LITT have been described primarily for the destruction of malignant or
benign tumors. Organs or tissues in which LITT has been used for this purpose
include the brain, head and neck, liver, kidneys, and prostate, among others.
More recently, high-power semi-conductor lasers developed for the
telecommunications industry have become popular owing to their reduced
power and cooling requirements and greatly reduced size. Diode laser
sources are commonly found at 810, 940, and 980 nm.
delivered through small, flexible optical fibers to reach remote areas
inside the body. LITT may be performed using a simple bare-tip optical
fiber or with a shaped (for example, ball-tip) fiber. However, a high
power density immediately adjacent to the fiber tip often leads to
char formation which limits penetration of optical radiation into the tissue.
As an alternative, diffusing optical fiber applicators have been developed
which emit light circumferentially into tissue over some length. Such
fibers have the advantages of reduced power density and an increased
optical delivery area.
In addition to a diffusing tip, some laser applicators may also include
provision for cooling of either the applicator and/or the tissue adjacent to
it. Cooled applicators can support higher power deposition rates and
may be less likely to fail or burn up than un-cooled applicators.
Recent studies explored the feasibility of multiple applicators to generate even larger lesions in one session. The principle is to split the laser beam in 2 or 4 beams and supply the radiation to 2 or 4 applicators. Of course one needs a more powerful laser, but the serial application has the benefit of supplying more heat between the applicators due to less draining of heat by perfusion. (References in German)
has tied LITT technologies with MRI, creating a highly precise procedure. The procedure is minimally invasive and has been reported in medical journals to be pain free and require a shorter recovery time.
in a minimally invasive manner and without the need for surgical removal, and with the absence of any adverse effect on the health and survival of the patient during intermediate followup . A forthcoming study of 24 patients has shown that small breast cancers can be effectively treated with ILT.
number of image-guided techniques including x-ray fluoroscopy, ultrasound
imaging, magnetic resonance imaging, or stereotaxic approaches. MRI
in particular, is attractive because dynamic MRI can be used to
infer temperature changes and/or other tissue changes as a potential
means of feedback during the LITT treatment.
Laser ablation
Laser ablation is the process of removing material from a solid surface by irradiating it with a laser beam. At low laser flux, the material is heated by the absorbed laser energy and evaporates or sublimates. At high laser flux, the material is typically converted to a plasma...
or laser thermal ablation, but this terminology is inaccurate since the goal of LITT is to destroy tissue through thermal coagulation and thermal necrosis rather than by removal (ablation).
Laser-tissue interactions
LITT is generally performed using optical radiation in the near-infraredwavelength range (from about 700 - 2000 nm), though when appropriate
chromophores are available, visible wavelengths (e.g. green) can also be
used. Photons launched into tissue meet one of three fates: scattering
Scattering
Scattering is a general physical process where some forms of radiation, such as light, sound, or moving particles, are forced to deviate from a straight trajectory by one or more localized non-uniformities in the medium through which they pass. In conventional use, this also includes deviation of...
,
absorption
Absorption (electromagnetic radiation)
In physics, absorption of electromagnetic radiation is the way by which the energy of a photon is taken up by matter, typically the electrons of an atom. Thus, the electromagnetic energy is transformed to other forms of energy for example, to heat. The absorption of light during wave propagation is...
, or exit from the tissue. When photons are absorbed, the energy from the photon is converted into inter- and intra-molecular
energy and results in generation of heat within the tissue.
At the same time the good absorption in tissue limits the size of the lesion created by the laser irradiation. So a compromise between good penetration and good absorption has to be found. After initial absorption the temperature generated spreads through the tissue and enlarges the lesion somewhat, dependent on the perfusion of the tissue. Large vessels will transport the heat away from the site and the effective temperature achieved is reduced.
As heating continues and tissue temperature is elevated, several processes occur which
lead to the destruction or death of the tissue:
At temperatures of 100 degrees Celsius or more, water in the tissue and in
the intracellular compartments may vaporize and lead to rupture or
explosion of cells or tissue components.
At temperatures above 60 degrees Celsius, proteins and cellular components of the tissue become severely denatured and coagulate leading to cell and tissue death.
At somewhat lower temperatures, generally above 45 degrees Celsius, prolonged
exposure leads to the thermal denaturation of non-stabilized proteins such
as enzymes. Though cell death is not immediate, destruction of critical
enzymes leads eventually to cell death.
Optical absorption in the near-infrared range is generally due to
combination aniuuud overtone bands of fundamental molecular stretches. For
wavelengths near 1000 nm, water is a primary absorber of optical energy.
History
The laserLaser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
was invented at Bell labs and first described in a paper
in 1958. A ruby laser as first constructed in 1960, and by the mid-1960s
medical applications were beginning to be explored. One of the first
publications of what was called laser endoscopy (which could essentially
be called LITT) was by S.G. Brown in 1968.
Medical laser applications grew somewhat steadily throughout the 1970s, but
in the 1980s exploded as new laser technologies and new and cheaper fiber
optics became available. After an initial boom, lasers generally settled into
a few niche areas in surgery and medicine.
In the 1990s, availability of new high-power and compact semiconductor
(diode) lasers increased the convenience of laser surgery, in particular
LITT. Since the early 1990s a number of surgical applications and investigations
of LITT have been described primarily for the destruction of malignant or
benign tumors. Organs or tissues in which LITT has been used for this purpose
include the brain, head and neck, liver, kidneys, and prostate, among others.
Lasers used for LITT
Throughout the history several Lasers have been used for LITT including Ruby lasers (690 nm) as well as visible gas lasers like Argon (514 nm). After the initial failures, the Lasers in the near infrared region and especially Neodymium:Yttrium-Aluminum-Garnite (Nd:YAG, 1064 nm, cw) were settled upon for best performance. These together with cooled applicators have created the largest lesions.More recently, high-power semi-conductor lasers developed for the
telecommunications industry have become popular owing to their reduced
power and cooling requirements and greatly reduced size. Diode laser
sources are commonly found at 810, 940, and 980 nm.
Applicators
A particular advantage of LITT is that large amounts of energy may bedelivered through small, flexible optical fibers to reach remote areas
inside the body. LITT may be performed using a simple bare-tip optical
fiber or with a shaped (for example, ball-tip) fiber. However, a high
power density immediately adjacent to the fiber tip often leads to
char formation which limits penetration of optical radiation into the tissue.
As an alternative, diffusing optical fiber applicators have been developed
which emit light circumferentially into tissue over some length. Such
fibers have the advantages of reduced power density and an increased
optical delivery area.
In addition to a diffusing tip, some laser applicators may also include
provision for cooling of either the applicator and/or the tissue adjacent to
it. Cooled applicators can support higher power deposition rates and
may be less likely to fail or burn up than un-cooled applicators.
Recent studies explored the feasibility of multiple applicators to generate even larger lesions in one session. The principle is to split the laser beam in 2 or 4 beams and supply the radiation to 2 or 4 applicators. Of course one needs a more powerful laser, but the serial application has the benefit of supplying more heat between the applicators due to less draining of heat by perfusion. (References in German)
Application in brain tumor treatment
Treating brain and spinal cord tumors can be difficult. The blood-brain barrier, which normally serves to protect the brain and spinal cord from damaging chemicals getting into those structures, also keeps out many types of chemotherapy drugs. Surgery can be difficult and risky due to proximity to critical structures, and radiation therapy can damage healthy tissue. LITT has been shown to be highly precise, allowing the physician to destroy only the targeted tissue, leaving healthy surrounding tissues unharmed (+/- 1mm). VisualaseVisualase
Visualase, Inc. founded in 2005 as a spin-off from BioTex, Inc., is focused on laser and image-guided technologies for thermal ablation. They developed the Visualase Laser Thermal Ablation System referred to as "Visualase" in which energy is delivered directly into a lesion. Light is delivered...
has tied LITT technologies with MRI, creating a highly precise procedure. The procedure is minimally invasive and has been reported in medical journals to be pain free and require a shorter recovery time.
Application in breast cancer treatment
Interstitial laser thermotherapy is an innovative method of treating breast cancersBreast cancer
Breast cancer is cancer originating from breast tissue, most commonly from the inner lining of milk ducts or the lobules that supply the ducts with milk. Cancers originating from ducts are known as ductal carcinomas; those originating from lobules are known as lobular carcinomas...
in a minimally invasive manner and without the need for surgical removal, and with the absence of any adverse effect on the health and survival of the patient during intermediate followup . A forthcoming study of 24 patients has shown that small breast cancers can be effectively treated with ILT.
Image guidance
Laser applicators for LITT may be inserted into target tissue using anumber of image-guided techniques including x-ray fluoroscopy, ultrasound
imaging, magnetic resonance imaging, or stereotaxic approaches. MRI
in particular, is attractive because dynamic MRI can be used to
infer temperature changes and/or other tissue changes as a potential
means of feedback during the LITT treatment.
See also
- Laser surgeryLaser surgeryLaser surgery is surgery using a laser to cut tissue instead of a scalpel. Examples include the use of a laser scalpel in otherwise conventional surgery, and soft tissue laser surgery, in which the laser beam vaporizes soft tissue with high water content...
- Laser ablationLaser ablationLaser ablation is the process of removing material from a solid surface by irradiating it with a laser beam. At low laser flux, the material is heated by the absorbed laser energy and evaporates or sublimates. At high laser flux, the material is typically converted to a plasma...
- Photodynamic therapyPhotodynamic therapyPhotodynamic therapy is used clinically to treat a wide range of medical conditions, including malignant cancers, and is recognised as a treatment strategy which is both minimally invasive and minimally toxic...
- EVLTEVLTEndovenous laser treatment is a minimally invasive ultrasound-guided technique used for treating varicose veins using laser energy.-Methods:...
- VisualaseVisualaseVisualase, Inc. founded in 2005 as a spin-off from BioTex, Inc., is focused on laser and image-guided technologies for thermal ablation. They developed the Visualase Laser Thermal Ablation System referred to as "Visualase" in which energy is delivered directly into a lesion. Light is delivered...