Delivering Thermal Energy in the Form of Water Vapor
In a hand-held delivery device connected to a generator, low power radiofrequency heats sterile water to approximately 103ºC. As the sterile water is transformed from liquid into steam, or vapor, the volume expands by almost 1,700 times and stores 540 calories of thermal energy for every milliliter (mL) of water.
A precise dose of water vapor thermal energy is delivered into the targeted tissue using a small needle with multiple emitter holes to ensure controlled and uniform vapor dispersion. The vapor is delivered into the targeted tissue at slightly above interstitial pressure, convectively driving the water vapor through tissue interstices, where it condenses and transfers the stored thermal energy directly to the targeted tissue. This convective heat transfer is what differentiates this RF thermotherapy from other ablative thermal therapies that rely on the slower, less precise and less efficient process of conduction to heat tissue.
Convective transfer of vapor thermal energy to tissue is fast but also self-limiting. Vapor condenses back into its liquid state as it is dispersed through tissue, so the energy travels no further than its intended area of treatment. The prostate is comprised of three separate zones or regions and the enlarged tissue that causes BPH is located in two of them – the transition zone and the central zone. The tissue separating these zones provides a natural anatomical barrier that contain the vapor within the intended treatment areas.
Convective transfer of thermal energy occurs only at the point of condensation. This release of thermal energy within the targeted area of treatment causes almost instantaneous death of tissue cell membranes, including the nerves, as well as collapse of the blood vessels. The body’s natural healing response then resorbs and removes the treated tissue, reducing the obstructive area.
Convective RF Water Vapor technology is an efficient means of transferring thermal energy. It is currently being used to treat BPH and is being assessed to treat other endourology conditions.