While most discussions surrounding newly diagnosed localized prostate cancer revolve around active surveillance, surgery, and radiotherapy, patients frequently inquire about high-intensity focused ultrasound (HIFU) as a potential treatment modality. In particular, patients want to know whether they should consider traveling abroad for this therapy, given that it is not currently approved in the United States.
As with any minimally invasive treatment, HIFU has been developed with the goal of decreasing pain and morbidity, as well as expediting recovery without any decrease in treatment effectiveness. Coupled with the substantial marketing efforts promoting HIFU, it is easy to understand why this topic frequently comes up in the clinic.
Ultrasound is considered “high intensity” if it is delivered with greater than 5 watts of power per centimeter-squared. It destroys tissue in two ways. First, the tissue absorbs the ultrasound wave and converts it into heat, leading to coagulative necrosis and tissue death as a result of thermal injury. Second, alternating cycles of compression and rarefaction lead to intertial cavitation. This effect causes tissue to die due to mechanical stress and is analogous to the way in which extracorporeal shock wave lithotripsy (ESWL) causes break-up of renal and ureteral calculi.
HIFU for prostate cancer is performed under anesthesia and utilizes an ultrasound probe in the rectum that emits a beam of focused ultrasound. This both allows visualization of the anatomy and delivers the energy that imparts the tissue effect. The probe also has a cooling balloon that protects adjacent tissue from the high temperatures generated by the focused ultrasound emitted from the probe. HIFU requires no incision and is an outpatient procedure, though patients do require Foley catheterization for 2 to 7 days. Additionally, transuretheral resection of the prostate (TURP) is often required just prior to the procedure.
There are two types of HIFU for prostate cancer—Ablatherm® (EDAP-TMS, France) and Sonablate® (Focus Surgery Inc, USA). Although both devices are approved in Canada, the European Union, South Korea, and Russia, neither is approved in the United States by the Food and Drug Administration. Key differences between the two systems are the types of tables used, patient positioning, power settings, treatment planning, and costs, with Ablatherm being the more expensive technology.1
There is a small body of evidence surrounding the use of each device, and much of the literature has severe methodological limitations. This includes observational study designs, small cohort sizes, insufficient follow-up, and inconsistent reporting of outcomes. Studies utilizing the Ablatherm device as primary therapy for localized prostate cancer have reported recurrence-free survival rates ranging from 66 to 77% at 5 years.2-8 Rates of bladder neck and urethral stricture are reported as 2 to 17%, and rates of urinary retention from 3 to 14%. Rectourethral fistula rates are reported to range from 0 to 3%. Studies evaluating Sonablate have similar statistics: Recurrence-free survival rates from 48 to 84% at 5 years, stricture rates of 4 to 30%, and urinary retention ranging from 1% to 13%.9-12 While incontinence is infrequent with these therapies (0.4% to 3%), erectile dysfunction occurs in 20 to 52% of men.