Surgery – Instruments – Light application
Reexamination Certificate
1999-01-29
2001-03-13
Dvorak, Linda C. M. (Department: 3739)
Surgery
Instruments
Light application
C606S002000, C606S011000, C606S020000, C606S023000
Reexamination Certificate
active
06200308
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to radiation treatment of tissue. More specifically, this invention relates to an improved dynamic cooling device and method in connection with radiation treatment of tissue.
BACKGROUND
Radiation surgery has been successfully employed to treat tissue. Radiation surgery involves the application of radiation to tissue to remove or alter the condition of the tissue. Radiation can be generated in the form of light from a laser or a lamp such as a flash lamp, or heat from an RF source. Alternatively, radiation can be generated in the form of microwaves or ultrasound.
Laser surgery has been successfully employed to remove hair and to treat skin abnormalities such as vascular lesions. For example, in performing a laser surgery, a beam of laser light having a selected wavelength is applied to a targeted region of the skin to selectively destroy the cutaneous blood vessels or melanin depending on the application. When removing unwanted hair, a beam of laser light is applied to the targeted skin. The light penetrates deep into the dermal tissue region, where the light is absorbed by peri-follicular melanin, reaching the follicle, bulb, bulge, and vascular supply to eliminate unwanted hair and impede its growth. In treating vascular lesions such as a port wine stain, laser light is preferentially absorbed by the hemoglobin which is the major chromophore in the blood in the ectatic capillaries in the upper dermis. The light energy is converted to heat, causing thermal damage and thrombosis in the targeted vessels.
Laser treatments, however, can be painful to a patient. To reduce pain, the cooling of tissue has been employed during laser treatment. U.S. Pat. No. 5,814,040, incorporated herein by reference, describes cooling an epidermal tissue region while performing selective photothermolysis of selected buried chromospheres in biological tissues using a laser. This cooling procedure is known as dynamic cooling. In this procedure, an epidermal tissue region is cooled by spraying with a cryogen to establish a predetermined dynamic temperature profile. The epidermal and underlying dermal tissue regions are subsequently irradiated to thermally treat the dermal tissue region while leaving the epidermal tissue region substantially undamaged. Cooling the epidermal tissue region reduces pain suffered by the patient during the procedure, and permits application of higher dosage radiation.
The GentleLase™ laser treatment system for hair removal and treatment of vascular lesions manufactured by Candela Corporation (Wayland, Mass.) employs dynamic cooling technology. The GentleLase™ laser treatment system includes a control unit and a handpiece. The control unit includes a flashlamp excited long-pulse alexandrite laser, a source of HFC 134a liquid cryogen, and electronics for controlling the system. The handpiece receives the laser light and the cryogen from the control unit through a cable which includes an optical fiber, wires, a delivery tube and an electronically controlled valve. The handpiece delivers the cryogen and the laser to tissue being treated. In the procedure, a highly focused spray of HFC 134a cryogen is applied on the patient's skin for 20-100 milliseconds, and after waiting 0-3 milliseconds, the laser pulse is applied to the patient's skin.
Clinical tests have shown that in order to achieve a desirable low temperature profile (e.g. −30° C. to 25° C.) in the epidermal tissue region, a waiting period after applying the cryogen of up to about 250 milliseconds is needed before applying the laser pulses. The desirable low temperature profile can vary depending on the skin tone of the patient and the objective in cooling. Only a few degrees below normal skin temperature may be sufficient when treating a patient having a light skin tone. On the other hand, when treating a patient having a dark skin tone, cooling to −30° C. may be desired. One problem encountered during dynamic cooling of an epidermal tissue region with a waiting period of up to about 250 milliseconds is that a bright light flash not associated with normal laser treatment has been observed during the procedure. The bright light flash resembles a flame, and tends to frighten the patients and interfere with light transmission. Therefore, a shorter waiting period of about 3 milliseconds which may be insufficient to obtain an optimal low temperature profile, is presently used to suppress the abnormal light flash. It is expected that similar flashing problems can occur during radiation treatment using other radiation sources.
SUMMARY OF THE INVENTION
The present invention provides methods and systems for performing radiation treatment of skin, while dynamic cooling the epidermal tissue region and minimizing or preventing light flashes from occurring. The radiation treatment can include removal of hair or treatment of pigmentation abnormalities (e.g. vascular lesions, tattoos, etc.).
In one aspect, the invention features a method for performing radiation treatment of skin having an epidermal tissue region and a dermal tissue region. In one embodiment, the epidermal tissue region is cooled by applying a cryogenic fluid to the epidermal tissue region. A gas flow is directed in the general direction of the epidermal tissue region to remove at least a portion of the cryogenic fluid applied to the epidermal tissue region. The skin is irradiated with a radiation source to treat the dermal tissue region subsequent to removing at least a portion of the cryogenic fluid. This method has been found to minimize or prevent an abnormal light flash from occurring during the laser treatment.
In one detailed embodiment, a non-reactive gas flow is directed in the general direction of the epidermal tissue region. The non-reactive gas flow can comprise air, nitrogen, or CO
2
. In another embodiment, a gas flow is directed in the general direction of the epidermal tissue region prior to and during application of the cryogenic fluid. In another detailed embodiment, skin is irradiated between 5 and 500 milliseconds, and more preferably between 50 and 200 milliseconds after applying the cryogenic fluid to the epidermal tissue region. In another detailed embodiment, a cryogenic liquid is applied to the epidermal tissue region and a cryogenic vapor formed, through the evaporation of the cryogenic liquid, is removed. In yet another detailed embodiment, the cryogenic fluid comprises a fluorocarbon compound having a ratio of fluorine to fluorine and hydrogen which is greater than about 0.75. The fluorocarbon compound is selected from a group consisting of: tetrafluoromethane; hexafluoroethane; octafluoropropane; chlorotrifluromethane; chloropentafluoroethane; dichlorodifluoromethane; 1,2-dichlorotetrafluoroethane; 1,1,1,2,3,3,3,-heptafluoropropane; pentafluoroethane; 2-chloro-1,1,1,2-tetrafluoroethane; trifluoromethane; 1,1,1,2,3,3-hexafluoropropane; and 2,2-dichloro-1,1,1-trifluoroethane.
In another embodiment, the method of performing radiation treatment of skin comprises the following steps. A first pulse of cryogenic fluid is applied to an epidermal tissue region for a first time period. After waiting a delay period of a predetermined time interval, a second pulse of cryogenic liquid is applied to the epidermal tissue region for a second time period. The delay period is sufficient to allow the first pulse of cryogenic fluid to cool the epidermal tissue region to reach a desired temperature profile. The skin is irradiated to treat an underlying dermal tissue region either during or immediately after application of the second pulse of cryogenic liquid, thereby minimizing or preventing an abnormal light flash from occurring during treatment.
In one detailed embodiment, a first pulse of cryogenic liquid is sprayed to the epidermal tissue region for a time period in the range from 10 milliseconds to 150 milliseconds, and a second pulse of cryogenic liquid is sprayed to the epidermal tissue region for a time period in the range from about 5 milliseconds to about 20 milliseconds after waiting
Durkin Anthony J.
Hsia James C.
Pope Karl
Candela Corporation
Dvorak Linda C. M.
Testa Hurwitz & Thibeault LLP
Yarnell Bryan K.
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