High-Intensity Focused Ultrasound: A Canadian Perspective

February 1, 2008

The use of high-intensity focused ultrasound (HIFU) as a method for ablation of a localized tumor growth is not new. Several attempts have been made to apply the principles of HIFU to the treatment of pelvic, brain, and gastrointestinal tumors. However, only in the past decade has our understanding of the basic principles of HIFU allowed us to further exploit its application as a radical and truly noninvasive, intent-to-treat, ablative method for treating organ-confined prostate cancer. Prostate cancer remains an elusive disease, with many questions surrounding its natural history and the selection of appropriate patients for treatment yet to be answered. HIFU may play a crucial role in our search for an efficacious and safe primary treatment for localized prostate cancer. Its noninvasive and unlimited repeatability potential is appealing and unique; however, long-term results from controlled studies are needed before we embrace this new technology. Furthermore, a better understanding of HIFU's clinical limitations is vital before this treatment modality can be recommended to patients who are not involved in well-designed clinical studies. This review summarizes current knowledge about the basic principles of HIFU and its reported efficacy and morbidity in clinical series published since 2000.

 

The authors have reviewed the published literature and in some cases the prepublication e-pub reports on high-intensity focused ultrasound (HIFU), providing commentary on the technology, outcomes to date, and a short comparative assessment of the two major commercially available device alternatives. They have also provided recommendations for urologists and patients who are interested in this relatively new, minimally invasive therapeutic alternative for patients with organ-confined prostate cancer.

Since May 2005, we have operated an Ablatherm Integrated Imaging HIFU device in Toronto, Ontario, through a private Canadian company-Maple Leaf HIFU. During that time we have treated in excess of 300 patients. The overwhelming majority of these have been patients with organ-confined disease seeking primary therapy with HIFU, as as an alternative to standard radical prostatectomy or ionizing radiation treatment. Maple Leaf HIFU is an investigative site of the EDAP-TMS–sponsored and US Food and Drug Administration (FDA)-approved cohort study currently enrolling patients.

 US Approval Lacking

The authors note that regulatory approval has been obtained in virtually all countries of the world save the United States. Ablatherm HIFU has been available as an alternative for patients suffering organ-confined prostate cancer in Western Europe since the mid-1990s, and an estimated 15,000 patients have been treated worldwide. Favorable reviews by Health Canada in October 2004 led to approval of the technology in Canada, and a similar National Health Service review in England carried out by the National Institute for Clinical Excellence resulted in approval in that country in 2005.

In our center, about one-third of the patients treated have been US residents who have chosen to travel to Toronto to be treated by Ablatherm HIFU. Canadian patients, in spite of the noninsured status of the modality, have also shown significant acceptance and interest in HIFU. The authors' recommendation-directed to US patients and urologists-that HIFU be undertaken "only as part of an ongoing US clinical study" leaves many patients in the United States without alternatives to traditional therapy since the current trials are quite restrictive in terms of entrance criteria.

Misconceptions About the Procedure

In their comparison of the two commercially available devices, the authors incorrectly state that treatment with Ablatherm HIFU requires a pretreatment transurethral resection of the prostate (TURP). While such pretreatment has been common in Western Europe, mainly as a result of system remuneration issues and cultural acceptance of ambulatory catheterization, this has not been the case in Canada, where fewer than 5% of patients treated by Ablatherm HIFU have had prior TURPs for either diagnostic or therapeutic reasons.

The authors' comments with respect to HIFU-related morbidity reflect published experience with early-generation Ablatherm devices. Our own experience using the third-generation Ablatherm Integrated Imaging Device (January 2006) is considerably different, particularly with respect to retreatment requirements, stenosis, and strictures. Of our 300+ patients (maximum follow-up of 30 months, mean follow up of 10.6 months), only 5 have required a second treatment, although admittedly follow-up remains short. We have made a similar observation with respect to stenosis and strictures, which in our series occur in less than 10% of patients. When they occur, however, these strictures can be difficult to deal with. Early posttreatment voiding difficulties related to sloughing of necrotic tissue remain common and, for patients, a vexing problem.

With respect to outcomes using the American Society for Therapeutic Radiology and Oncology (ASTRO) biochemical failure criteria, our own results-again, admittedly short term-exceed those in the currently published literature. This may be the result of our having used third-generation technology virtually throughout our series. These results will shortly be submitted for peer-reviewed publication and have already been presented in several forums.

Conclusions

The authors' cautionary conclusions with respect to HIFU treatment of localized prostate cancer predictably call for larger trials with longer follow-up. In the United States, such trials will in all likelihood have to await FDA approval, which is currently projected to be at least 3 years away. Outside of the United States, where approval is widespread, patient access will continue to improve and more mature research data will be published in support of this very promising new treatment modality.

 

-William L. Orovan, MD, FRCS, FACS