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.
The Sonablate system also has extra safety features that are built in to allow adjustments for the thickness of the rectal wall, and the visual guidance allows the physician to stop treatment if it is found that the prostate has moved back towards the bladder. Color Doppler imaging is utilized during the procedure to assist the surgeon to identify the neurovascular bundles, those structures that are responsible for erectile function, and to allow nerve sparing treatments.
So who is a candidate for this technology? Patients must have organ-confined prostate cancer. The size of the prostate has some bearing on treatment planning. Prostates that have a height of 40mm or less can be safely treated with the Sonablate technology, however, the Ablatherm system can only treat a maximum height of 24mm. Patients with prostates that exceed this dimension, which is a common finding, must undergo a preliminary transurethral resection of the prostate (TURP) prior to undergoing treatment with HIFU.
A very recent study has given some indication as to the great promise for the future of this technology (Lancet Oncology DOI:10.1016/S1470-2045(12)70121-3). This prospective study has demonstrated that the common side effects of urinary incontinence and erectile dysfunction that are seen with treatments for localized prostate cancer are significantly reduced in patients undergoing HIFU. Additionally, early cancer control has been demonstrated in this study. An additional study published in the Journal of Urology (185:1246-25) has demonstrated satisfactory results for patients who have been treated with focal therapy (treatment only in those parts of the prostate that contain cancer) with 89 percent of men at one year being dry, sexually active and with evidence of cancer control. This compares very favorably with results obtained with alternative therapies. An additional study (Br J of Cancer, 2009, 1-8) also identifies HIFU as a safe effective means of treating localized prostate cancer.
In my opinion HIFU is being proven to be a safe, effective means of treating localized prostate cancer. It is important to note that HIFU is only approved for investigational use within the U.S. and is being studied for the treatment of recurrent prostate cancer in clinical trials in the U.S. The FDA has made no decision as to the safety or efficacy of the technology for the treatment of prostate cancer. Currently, this technology is available for the treatment of prostate cancer outside the U.S. in more than 30 countries where the technology is approved. Patients who wish to undergo this form of therapy should discuss this with their Urologist.
Published On: May 04, 2012