Abstract: The present application discloses a method and device for locating and mapping the cavernosal nerve bundle by electro-stimulation to enable safe and effective implantation of radioactive seeds for prostate brachytherapy. By locating and mapping the cavernosal nerve bundle prior to seed implantation, the brachytherapist can make intra-operative decisions to avoid mechanical and radiational injury to the nerve which results in impotency or other prostate-Urethral complications. The device of the invention takes the form of an automated closed-looped electro-stimulating system having a handle for manipulating the device, a stimulating tip for applying an electro-stimulus to a tissue site, a control unit to activate and terminate application of the electro-stimulus and to interpret a tumescence response, a sensor for detecting and measuring a tumescence response, a patient ground return, and a display monitor to indicate the nature, stability and strength of the tumescence response to the brachytherapist.