Computer guided cryosurgery

#The inventions described herein relate to the field of cryosurgery and ablative surgery.

#The system and methods described below enhance the accuracy and effectiveness of cryosurgery of the prostate. Cryosurgery of prostate is an effective treatment for prostate cancer and benign prostate hyperplasia, conditions which affect many men.

#The use of cryosurgical probes for cryoablation of prostate is described in Onik, Ultrasound-Guided Crvosurgerv, Scientific American at 62 (January 1996) and Onik, Cohen, et al., Transrectal Ultrasound-Guided Percutaneous Radial Cryosurgical Ablation Of The Prostate, 72 Cancer 1291 (1993). In this procedure, generally referred to as cryoablation of the prostate, several cryosurgical probes are inserted through the skin in the perineal area (between the scrotum and the anus) which provides the easiest access to the prostate. The probes are pushed into the prostate gland through previously placed cannulas. Placement of the probes within the prostate gland is visualized with an ultrasound imaging probe placed in the rectum. The probes are quickly cooled to temperatures typically below -120 C. The prostate tissue is killed by the freezing, and any tumor or cancer within the prostate is also killed. The body will absorb some of the dead tissue over a period of several weeks. Other necrosed tissue may slough off through the urethra. The urethra, bladder neck sphincter and external sphincter are protected from freezing by a warming catheter placed in the urethra and continuously flushed with warm saline to keep the urethra from freezing.

#FIG. 1 is an overview of the transperineal cryosurgical ablation of the prostate.

#FIG. 2 is an illustration of a sagittal or longitudinal cross section of the prostate and surrounding anatomy as displayed on the video display provided by the system.

#FIG. 3 is an illustration of a horizontal or transverse cross section of the prostate and surrounding anatomy as displayed on the video display provided by the system.

#FIG. 1 shows one of the basic operations for which the cryoprobes are designed. Several probes 1, 2, 3, 4 and 5 are shown inserted in the prostate 6 (in some instances a sixth probe, not shown, is used). All five probes are inserted through the perineal region 7 between the scrotum and the anus. Probes 2 and 3 are shown inserted into the anterior lobe 6a of the prostate, and Probes 1, 4 and 5 are shown inserted into the posterior lobe 6p, which is larger than the anterior lobe. The probes are placed within the prostate according to procedures well known in the art, and a suitable procedure is described in step-by-step detail in Onik, et al., Percutaneous Prostate Cryoablation, (1995) at pages 108-112 and Onik, Ultrasound-Guided Cryosurgery, Scientific American at 62 (January 1996). Typically five or six probes are used in the procedure, though more or less may be used when required by unusual anatomy of a particular patient. The urethra 8 which passes through the prostate is one of the anatomic structures that usually should not be frozen during this surgery. Accordingly, the urethra is protected and kept warm with the urethral warming catheter 9. The bladder neck sphincter 10 and the external sphincter 11 are also structures that should be protected from freezing, and these are protected from freezing by the warming catheter. Neurovascular bundles on the right and left of the prostate should also be protected from freezing. Transrectal probe 13 is inserted into the rectum 14 in order to visualize the placement of the probes and the growth of the iceballs formed by the cryoprobes. To assist in placement of the cryosurgical probes, a template 15 is used which supports the probes during insertion and while they are installed in the body. The patient is placed horizontally on an operating table with legs positioned to provide access for the ultrasound probe to be inserted into the rectum and cryoprobes to be inserted through the perineal area into the prostate.

#The transrectal ultrasound probe 13 is used to visualize the prostate and the cryosurgical probes. The ultrasound probe operates in the range of about 2-10 MHz, depending on the equipment used (the process described herein may be used with any ultrasound probe and ultrasound generator, which may be selected based on various technical, medical and budgetary considerations). The image is displayed as a two dimensional representation of the boundaries of the prostate, as illustrated in FIGS. 2 and 3.

#FIG. 2 shows a longitudinal (also referred to as saggital or coronal) cross section of the prostate, generally denoted by the ultrasound outline 21. The top, bottom, anterior and posterior sides of the outline are delineated by the letters T, B, A and P, respectively. The apex of the prostate 22 points generally to the perineal area shown in FIG. 1. Other anatomical structures visible in display include the urethra, whose outline 23 may not appear fully in the coronal cross section. The urethral warming catheter image 24 appears within the urethra. Also, the ultrasound image of the rectal wall 25 appears along the bottom of the display area, and the image of the ultrasound probe 26 may appear directly below the rectal wall. The rectum and rectal wall are preferably straightened by the pressure exerted by the insertion of the ultrasound probe, as explained below, to set up the system for the calculations and displays described below. Since the prostate is generally oblong in this direction, and longer in this direction than in the horizontal or transverse cross section, we refer to this cross section as the longitudinal cross section.