Surgery – Instruments – Light application
Reexamination Certificate
1998-06-30
2001-03-13
Dvorak, Linda C. M. (Department: 3736)
Surgery
Instruments
Light application
C606S009000, C607S089000, C372S003000
Reexamination Certificate
active
06200309
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to photodynamic therapy, and, more particularly to photodynamic therapy using an irradiation source derived from a phased array Raman laser amplifier.
Photodynamic therapy (“PDT”) is an emerging modality in which a photosensitizing drug localizes to diseased tissue upon introduction into the body and it then is activated by light of a specific wavelength. The photosensitizers have biolocalization properties and are optically excitable. That is, upon introduction, there is a period of time during which the photosensitizer is absorbed by all cells, but thereafter, the agent rapidly leaves most normal cells while remaining in any tumerous cells in organs and diseased tissues for a longer period of time. The treated cancer cells are then exposed to light from a laser chosen for its ability to activate the photosensitizing agent. Typically, laser light is focused into a beam so it can be aimed at a specific area of the body being treated, and the laser light normally produces a narrow range of light frequencies. It is known in the PDT field that light in the 600-1000 nm spectral region (the “phototherapeutic window”) possesses maximum penetration power into most human tissues owing to the low absorptivity of the normal cell constituents in this region and the relatively inefficient scattering of red light by cell organelles. Therefore, red light, in particular, possesses a high penetration power into human tissues and can be selectively absorbed by red-light-absorbing photosensitizing agents (e.g., certain known porphyrins, chlorins, carbocyanines, phthalocyanines, naphthalocyanines, and derivatives thereof) localized in predetermined sites of the organism.
In any event, photosensitizer agents are used in PDT that capture the light energy at the specific wavelength generated by the laser to create an excited state molecule that causes localized tissue destruction in the presence of oxygen without causing damage to the surrounding healthy tissues. Namely, after absorbing the light of the appropriate wavelength, the photosensitizer becomes activated to a higher energy state capable of generating singlet oxygen molecules that react with cellular components to induce cell death, i.e., they have cytotoxic effects. The light exposure must be timed carefully so that it occurs when most of the photosensitizing agent has left healthy cells but is still present in cancerous ones.
There is a great deal of interest in developing PDT in the oncology field because it does not cause the severe side effects of chemotherapy and radiation therapy, such as nausea, diarrhea, hair loss, and organ failure, and it is less invasive than surgical excision in the case of skin surface cancers. Also, PDT can be used in conjunction with, and not to the exclusion of, conventional cancer treatments, such as with cancer drugs or radiation.
For instance, the standard therapy for skin tumors has been surgical excision. However, photodynamic therapy based on the phototoxicity of photosensitizing agents, such as porphyrins which are the natural precursors of hemoglobin, recently have been effectively used for treatment of skin tumors. Topical application of porphyrins followed by tumor exposure to red light (e.g., in the 630-670 nm &lgr; range) has been shown to be an effective therapy for several types of tumors, such as for solar keratoses, superficial basal cell carcinomas of the skin and Bowen's disease. Also, the U.S. Food and Drug Administration has approved a photosensitizing agent called dihematoporphyrin ether/ester (DHE), or Photofrin-R™, to relieve symptoms of esophageal cancer that is causing obstruction and for esophageal cancer that cannot be satisfactorily treated with lasers alone.
However, a problem in the PDT field is that no one type of photosensitizer agent can be universally employed for all conceivable PDT treatments due to the physicochemical, photochemical and photophysical peculiarities of any given photosensitizer agent. Also, some currently used photosensitizer agents for PDT are unstable in vivo or induce hyper-photosensitivity in the patient in the case of certain hematoporphyrins and their derivatives used in treatment of skin tumors. This is spurring continuing research into development of a new generation of PDT photosensitizer agents that avoid these drawbacks. Also, the field is interested in developing photosensitizers that can be effectively used in PDT treatments where needed to deeply penetrate tissues to reach the malignant cells, among other things. As a consequence, new types of photosensitizer agents for PDT are being rapidly researched and developed on an ongoing basis.
These different types of photosensitizer agents can and often do require irradiation at vastly different wavelengths relative to one another for achieving excitation. Also, a laser is needed that operates at an appropriate power level to accommodate factors such as penetration depth of the beam into living tissue. To meet this challenge, practioners in the PDT field have previously resorted to case-by-case searches for laser equipment having wavelength and power attributes that match the requirements of the particular photosensitizer agent desired to be tested or used for a given PDT procedure. This can be a time-consuming process even if an acceptable laser-photosensitizer agent match is ultimately made. Moreover, given that each different type of laser equipment represents a relatively expensive piece of hardware, it also can be costly to proceed in this manner where a wide array of photosensitizer agents are expected to be employed.
Consequently, from the above, it can be appreciated that the scope and potential of PDT could be substantially improved if more versatile laser systems could provided that could accommodate the optical requirements of a wide diversity of photosensitizer agents. The operation of a single efficient laser source for PDT treatments in general at different selectable arbitrary wavelengths for the treatment and photosensitive materials at hand would be of enormous advantage. It is Applicants' recognition that what is needed in this regard is a narrow line width, single frequency-selectable solid state laser amplifier that is both compact and efficient.
Furthermore, to understand the backdrop of laser technology to the present invention, some discussion is thought appropriate on the state of Raman shifted solid state laser technology. One laser transmitter in this regard which has high power output characteristics is a Master Oscillator—Phased Power Amplifier Array (MO)-(PPAA) laser system previously disclosed in commonly-assigned, U.S. application Ser. No. 08/782,175, which was filed on Jan. 14, 1997, now U.S. Pat. No. 5,847,816, and which patent is incorporated herein by reference for all purposes.
As illustrated in
FIG. 1
, the MO-PPAA laser system includes a MO
100
coupled to a fiber optic power amplifier
200
. MO
100
is a stable, very narrow line width, laser, which is operating in a TEM
00
mode at a frequency within the gain spectrum of the power amplifier
200
and which can be coupled by optical fiber to deliver a continuous wave signal to downstream components (not shown).
It will be appreciated that the master oscillator laser
100
can be any conventional master oscillator laser, although the master oscillator is likely a fiber laser oscillator. Some additional conventional components are understood to be part of any practical MO-PPAA laser system and have been omitted. For example, one of ordinary skill in this particular art would appreciate that an optical isolator would be located immediately downstream of the master oscillator
100
to prevent feedback from downstream components, e.g., power amplifier
200
, that would induce instability in the master oscillator
100
. The details of such components are well known to those skilled in the art and will not be discussed further.
Although a single fiber power amplifier
200
will suffice for some short range applications, a coherent array
Rice Robert R.
Zediker Mark S.
Dvorak Linda C. M.
Farah Ahmed
McDonnell Douglas Corporation
Powell, Jr. Raymond H. J.
Westerlund Robert A.
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