Surgery – Instruments – Cyrogenic application
Reexamination Certificate
1998-11-16
2001-02-20
Dvorak, Linda C. M. (Department: 3739)
Surgery
Instruments
Cyrogenic application
C606S020000, C606S023000
Reexamination Certificate
active
06190378
ABSTRACT:
BACKGROUND OF THE INVENTION
Cryosurgery, a surgical procedure in which a target area of a patient is frozen, is known for treating various medical conditions. Most often, cryosurgery is used in the treatment of cancer, in which a cancerous mass or tumor is destroyed during the freezing process. Over time, the frozen mass deteriorates and is consumed by the body. One application for cryosurgery is in the treatment of prostate cancer.
Prostate cancer is one of the most frequently diagnosed malignancies in American males and is the second leading cause of cancer related deaths. Successful treatment requires confining the cancer to the prostate gland and surrounding tissue, referred to as the prostatic capsule, in order to prevent the spread and metastasizing of the cancer.
In addition to cryosurgery, other conventional treatment therapies for prostate cancer include radical prostatectomy, radiation therapy and medical or surgical castration. In radical prostatectomy, the prostate gland and a margin of the surrounding tissue are surgically removed. However, a relatively high rate of recurrent, or residual tumors have been reported following radical prostatectomy. Further, this form of treatment suffers from a relatively high rate of impotence and/or incontinence.
In radiation therapy, radiation is applied to the prostate gland either by an external source or by radioactive implants. However, in many reported cases, the ability of radiation therapy to control cancer has been found to last only a few years.
Medical castration involves the administering of drugs that shut down a bodily process, such as the production of testosterone or the effect of testosterone on the prostate gland. This form of therapy does not cure the cancer and, over time, the cancer usually progresses. Surgical castration does not appear to be any more effective than medical castration and both types of castration can cause hot flashes, loss of sex drive, enlargement of the breasts and impotence.
Prostate cryosurgery involves the use of multiple liquid nitrogen or gas cooled probes (i.e., cryoprobes) inserted into the prostate through the perineum to freeze the prostate gland, thereby killing the cancer. Typically, five cryoprobes are used and the frozen area around each cryoprobe is sometimes referred to as an “ice ball.” An ultrasound probe is used to guide the cryoprobes into position in the prostate and to permit the physician to visualize the edge of the ice balls or the overall ice ball formed by the cryoprobes. Temperature sensing thermocouples are positioned external to the prostatic capsule to measure the surrounding temperatures.
By visualizing the edge of the ice balls and monitoring the temperature adjacent to the prostate gland, the physician controls activation of the cryoprobes in an effort to ensure that the entire cancerous area is frozen and further, to ensure that adjacent areas are not frozen in order to prevent certain side effects. In particular, freezing nerves adjacent to prostate or the seminal vesicle can cause impotence and freezing the urethra, bladder or the rectal sphincter muscle can cause incontinence problems. During the cryosurgical procedure, generally, a warm fluid is directed through the urethra which passes through the prostate gland in order to help prevent freezing of the urethra.
Since ultrasound provides a two-dimensional image, only the edge of the ice balls can be visualized and thus, the physician is not provided with any information regarding temperatures behind the ice ball edge. Further, the edge of the ice ball is at approximately 0° C. and, in order to effectively destroy cancer, the tissue must be frozen to temperatures between approximately −20° C. and −40° C. Thus, the physician must estimate what portion of the ice ball has effectively destroyed the cancer. This task is complicated by the fact that ice ball formation is dependent on certain physiological parameters of the patient, such as blood flow and tissue properties.
Although prostate cryosurgery has not been in use as long as the other prostate cancer treatment therapies, it has displayed nearly an eighty-percent success rate in destroying prostate cancer. Further, prostate cryosurgery has the advantage that patients usually do not suffer serious urinary control problems. However, the success of prostate cryosurgery in destroying cancer without causing impotence and other side effects is dependent on the precision with which the entire cancerous area and no additional area is frozen.
BRIEF SUMMARY OF THE INVENTION
The invention relates to a cryosurgical instrument including at least one, and preferably a plurality of cryoprobes adapted for being positioned in tissue of a patient targeted for cryosurgery, such as the prostate gland, and operative to form an ice ball in the tissue upon activation. Each of the cryoprobes has a sheath disposed over at least a portion thereof which supports at least one measuring device for measuring a parameter of the tissue of the patient. Preferably, the measuring device is embedded in the sheath and measures tissue temperature, thermal conductivity, blood perfusion rate and/or thermal diffusivity. In one embodiment, the sheath includes a plurality of measuring devices embedded therein and spaced along a portion of the sheath both axially and longitudinally.
The instrument further includes a processor for predicting formation of an ice ball by each of the cryoprobes in the tissue over time and a display for displaying the ice ball formation prediction. More particularly, the processor is responsive to an output signal of the measuring device indicative of a measurement performed prior to cryosurgery for providing the ice ball formation prediction. The processor is further responsive to a model of the thermal properties of the tissue of the patient and to the effect of urethral warming. The display provides a representation of the temperature contours within the prostate gland that would result from activation of the cryoprobes. With this arrangement, a physician is able to perform “trial” cryosurgical procedures without activating the cryoprobes in order to determine an optimum treatment procedure.
In one embodiment, the measuring device is further operative to measure a parameter of the tissue following activation of the cryoprobes (i.e., during cryosurgery). The processor is responsive to this “surgery” measurement for verifying the ice ball formation prediction. The cryosurgical instrument may further include an impedance measurement circuit coupled to selected ones of the cryoprobes for providing an output signal indicative of the tissue impedance with which the ice ball formation prediction is verified.
Also provided is a method of predicting ice ball formation by one or more cryoprobes in tissue of a patient targeted for cryosurgery including the steps of forming a model of the thermal properties of the tissue of the patient and measuring at least one parameter associated with the tissue of the patient prior to activation of the cryoprobes. The method further includes predicting the formation of the ice balls by the cryoprobes in the tissue of the patient in response to the model and the measured parameter. The method may further include the step of measuring a tissue parameter following activation of the cryoprobes and verifying the ice ball formation prediction based on this “surgery” measurement. Further optional steps include measuring the impedance of the tissue and verifying the ice ball formation prediction based on the measured impedance.
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Daly, Crowley & Mofford LLP
Dvorak Linda C. M.
Massachusetts Institute of Technology
Ruddy David M.
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