Rectal protection during prostate cryosurgery: design and characterization of an insulating probe

This study presents the design and characterization of an insulating probe made of silicone that could be used for enhancing the safety and efficacy of prostate cryosurgery. The probe would be placed in Denonvilliers' fascia between the prostate and the rectum prior to freezing. During freezing, the iceball would be monitored by ultrasound through the silicone, and direct temperature monitoring of the rectal and prostatic tissue via thermocouples mounted on opposing sides of the device. Both theoretical and experimental studies were performed to verify the insulating and acoustic properties of the probe. The insulating effect of the silicone will enhance cell death within the prostate while minimizing tissue freezing injury and therefore fistula formation postfreeze in the rectum. Experiments were also performed with the insulator placed in gelatine which showed that the silicone material is transparent to ultrasound. In addition the silicone was itself visible under ultrasound imaging, a characteristic which may assist in the delivery of the device to the surgical site. One possible scenario for reconfiguration and delivery of the device is suggested prior to a cryosurgery. The success of this device in insulating and monitoring temperature during freezing suggests that it can also be useful in protecting sensitive tissues adjacent to a surgical site when extreme heat is applied (i.e., electron or hyperthermic surgery).