Cryotherapy Simulator for Localized Prostate Cancer James K. Hahn, Ph.D. 1 , Michael J. Manyak, M.D. 2 , Ge Jin 1 , Dongho Kim 1 , John Rewcastle, Ph.D. 3 , Sunil Kim, Ph.D. 4 , and Raymond J. Walsh, Ph.D. 2 1 Institute for Computer Graphics 2 Department of Urology , School of Medicine and Health Sciences The George Washington University 3 Department of Radiology, University of Calgary and Endocare Inc. 4 Department of Biomedical Engineering, Hanyang University Abstract. Cryotherapy is a treatment modality that uses a technique to selectively freeze tissue and thereby cause controlled tissue destruction. The procedure involves placement of multiple small diameter probes through the perineum into the prostate tissue at selected spatial intervals. Transrectal ultrasound is used to properly position the cylindrical probes before activation of the liquid Argon cooling element, which lowers the tissue temperature below -40 degrees Centigrade. Tissue effect is monitored by transrectal ultrasound changes as well as thermocouples placed in the tissue. The computer-based cryotherapy simulation system mimics the major surgical steps involved in the procedure. The simulated real-time ultrasound display is generated from 3-D ultrasound datasets where the interaction of the ultrasound with the instruments as well as the frozen tissue is simulated by image processing. The thermal and mechanical simulations of the tissue are done using a modified finite-difference/finite-element method optimized for real-time performance. The simulator developed is a part of a comprehensive training program, including a computer-based learning system and hands-on training program with a proctor, designed to familiarize the physician with the technique and equipment involved. 1. Introduction Prostate cryotherapy is a relatively new procedure for prostate cancer in which the prostate gland is treated in situ by freezing. The freezing and thawing process destroys the prostate glands, which are replaced by scar tissue following the procedure. This is accomplished by inserting several cylindrical cryoprobes into the gland under ultrasound guidance. Thermocouples are placed at strategic locations within and around the gland to monitor the formation of ice crystals around the cryoprobes which occurs when the cryoprobes are activated. The ability of a physician to deliver an efficacious freezing injury is largely dependent on clinical experience and the ability to create an area of treatment known as an ‘iceball’ that kills the target cancerous tissue without damaging surrounding tissues. A prostate cryotherapy simulator has been developed to expedite the learning process associated with this technically demanding procedure. Three dimensional ultrasound images of the prostates from real patients are used. The physician can practice prostate cryotherapy in a clinically realistic manner by placing and operating the cryoprobes before actually treating a patient. During a clinical procedure the physician monitors the iceball growth on ultrasound and also uses the temperature measurements from the thermocouples