Novel Optical Methods for Identification, Imaging, and Preservation of the Cavernous Nerves Responsible for Penile Erections During Prostate Cancer Surgery

PUBLIC ABSTRACT

Approximately 235,000 men in the United States were diagnosed with prostate cancer in 2006. About 60,000 of these men underwent surgery to remove a cancerous prostate. One of the greatest challenges of prostate cancer surgery is preservation of sexual function, which directly relates to quality of life issues for men after surgery. There has been a wide variability in reported sexual potency rates after prostate cancer surgery, ranging from 21%-86%. This variability may be due, in part, to our limited understanding of the location, extent, and course of the cavernous nerves, which are responsible for erectile function. The cavernous nerves exist as two distinct bundles of microscopic nerve fibers that course along the surface of the bladder, prostate gland, and urethra. Because of the close proximity of the nerves to the surface of the prostate, they are at serious risk of damage from both mechanical and thermal injury during dissection and removal of a cancerous prostate gland. In addition, their microscopic nature makes it difficult to predict the true course and location of these nerves from one individual patient to another. Improvements in identification, imaging, and visualization of these nerves will likely improve the consistency of nerve preservation and postoperative potency and thus lead to direct patient benefit. New methods for identification, imaging, and precise dissection of the cavernous nerves form the prostate would be of great use in aiding surgical preservation of the cavernous nerves during surgery.

We propose in this grant application to apply three different new optical technologies to better identify, image, and preserve the cavernous nerves during prostate cancer surgery, with the goal of improving the rate of sexual function and quality of life of patients after surgery:

(1) Non-Contact Laser Stimulation of the Cavernous Nerves: Low-energy laser pulses will be sent into the tissue and then the erectile response at the penis will be measured upon optical stimulation. Currently, electrical stimulation techniques are being used, but they have proven inconsistent and unreliable. Electrical nerve is limited by the need for physical contact between the electrode and the tissue, which may result in tissue damage. The spatial precision of the stimulation is also limited by the size of the electrode. The electrical stimulation itself produces artifacts that may interfere with the measurement. Laser nerve stimulation offers several advantages over electrical stimulation including: (1) non-contact method of stimulation, (2) improved spatial selectivity, and (3) elimination of stimulation artifacts. Preliminary studies in our laboratory have successfully demonstrated non-contact laser stimulation of the cavernous nerves. We propose to optimize the laser nerve stimulation system for potential use as a tool during prostate cancer surgery for identifying the exact location of the nerves.

(2) High-Resolution Imaging of the Cavernous Nerves using Optical Coherence Tomography (OCT): OCT is a relatively new noninvasive optical imaging technology used to perform real-time, high-resolution, cross-sectional imaging near the cellular level by measuring backscattered near-infrared light. OCT image resolutions are 10-100 times better than with ultrasound. Preliminary studies in our laboratory have demonstrated that OCT is capable of discriminating the cavernous nerves from surrounding prostate tissue during rat studies. We propose to optimize the OCT system for potential use in imaging the cavernous nerves during prostate cancer surgery.

(3) Precise Laser Dissection of the Prostate Gland without Damage to the Cavernous Nerves: The majority of laparoscopic techniques for prostate cancer surgery use energy sources to dissect the cavernous nerves off of the prostate. However, the use of energy sources for thermal coagulation of blood vessels so close to the nerves frequently causes damage to the nerves, resulting in loss of erectile function. We propose to optimize a KTP laser, which emits green light that is preferentially absorbed by red blood vessels, for precise laser dissection of the prostate. Since the prostate is a highly vascular tissue, the laser will be able to cut out the prostate without damaging the adjacent cavernous nerves.