In this era of minimally invasive medicine, High Intensity Focused Ultrasound (HIFU) deserves mention as a suitable option for ablative therapy for the treatment of organ-confined prostate cancer, and as a possible alternative to the more widely utilized treatments such as radiation therapy, robotic surgery or cryotherapy.
HIFU is a minimally invasive, outpatient based technology that utilizes highly focused ultrasound energy to destroy a precise and preselected area of tissue. To better understand the workings of HIFU, it is easy to compare this to children using a magnifying glass above a leaf to focus the sun on the leaf causing it to burn. If your hand were placed directly in front of the magnifying glass where the sun’s rays are broad and unfocused, the heat would not be felt on your hand; however, if your hand were placed at the focal point, the small focused area concentrated by the magnifying glass, heat would be felt.
When treating the prostate, the focal point or target zone is located within the prostate while other tissue, such as the rectum, is kept in the area where concentration of energy should not occur. By magnifying this ultrasound energy, heat is generated at the focal point and the temperature can rise to 90 degrees Centigrade (~190 degrees Fahrenheit). The thermal effect of HIFU destroys tissue along with the mechanical effect, called cavitation, which occurs as the ultrasound wave creates negative pressure within the tissue.
There are two competing HIFU technologies, Ablatherm and Sonablate. Each treating physician will have a preference for each technology, however, there are some basic differences and, in my opinion, advantages to the Sonablate technology. Both technologies involve a rectal probe that will provide ultrasound imaging and treatment. The Sonablate uses a robotic high definition 6.5 Mhz imaging transducer and 3.0 Mhz and 4.0 Mhz treatment transducers that allows real time imaging. The images are taken in the transverse and sagittal plane as well as a 3-D image for planning in the coronal plane. The competing Ablatherm device is not capable of providing a real sagittal image as it relies solely on a computer rendition. Additionally, the robotic Sonablate device allows for the treatment of larger prostates and more precise energy placement due to its advanced transducer technology. The Sonablate area of treatment can be as small as 10mm while the competing technology is limited to 19mm.
Technology innovation also sets the devices apart. The Sonablate is the only device that incorporates Tissue Change Monitoring (TCM) software and Neurovascular Bundle Detection (NVB) software into its system. This allows for real time feedback regarding energy deposition and identification of critical structures around the prostate, such as the nerve bundles that control erectile function.
One of the other most critical differences in the two technologies is the ability to control energy with the Sonablate system. The surgeon is allowed to adjust the power based on the tissue response that is visualized. TCM software assesses the tissue response to each pulse, and the doctor can retreat any area of tissue that does not show sufficient change in the tissue after it has been initially treated. Visual changes generated in the tissue also determine the amount of energy needed to perform an optimum treatment. This allows for a more complete treatment.