Magnetic resonance-guided focused ultrasound (MRgFUS) treatment of uterine fibroids in an outpatient practice can yield net perfused volume (NPV) and shrinkage greater than previous results, according to study data presented on Sunday at the 2008 meeting of the Radiological Society of North America (RSNA).  "The original pivotal study guidelines put out by the FDA limited the treatment of fibroids to 33% of each fibroid, but this was lifted to 50% of all fibroids under the expanded treatment guidelines," reported Suzanne LeBlang MD, Neuroradiologist at University MRI & Diagnostic Imaging Center, who presented the study. (Read the abstract here.) "Similarly, the amount of time allowed to treat the fibroid was limited to 120 minutes under the pivotal study guidelines and this has been relaxed to a limit of 180 minutes under the expanded treatment guidelines."

The greater the non perfused volume (NPV=the amount of the fibroid killed during the treatment), the greater the shrinkage, specifically, for non perfused volumes OF 0 to 50% there was average shrinkage of 14%, but for non perfused volumes of 75% to 100% there was average shrinkage at 6 months of 51%. As prior studies have already proven the relationship between increased NPV and increased shrinkage with improved symptomology, we can expect more complete symptomatic relief. A linear regression analysis between NPV ratio and 6 month shrinkage showed a statistically significantly (P<0.0001) correlation. Dr. LeBlang explained, "Our results of increased tumor shrinkage with increased non perfused volume ratios exceeded that shown in previous studies due to more relaxed treatment guidelines and improved operator experience: the average shrinkage from the initial pivotal study was 15% whereas in our study the average shrinkage was 33%."

In two subsequent presentations, safety and candidacy issues for MRgFUS were discussed. A total of 200 candidates with symptomatic uterine fibroids that passed initial evaluation criteria had screening MRI over a four year period. "We determined that 73% of women screened with MRI scans with and without contrast are candidates for MRgFUS," Dr. LeBlang said in an interview with MedicExchange. (Watch the slides and listen to the audio of the entire interview here.) The main factors excluding candidates were alternate diagnosis (26/61), with the most common: adenomyosis – 12 patients, intracavitary polyps/fibroids -7 patients, and possible cancer -7 patients. "The other patients that do not seem to be good candidates for the MRgFUS procedure had multiple varied exclusion criteria the most significant of which were alternative diagnoses such as diffuse adenomyosis with fibroid, endometrial lesions, metallic clips along the beam path, fibroids that are too numerous or too large, hemorrhagic fibroids, pedunculated/nonenhancing fibroids and cancer."

Another potential exclusion criterion is an enlarged subcutaneous fat and muscle layers. A total of 118 patients from a four year period were retrospectively reviewed for pre-treatment scans and post-treatment scans. Dr. LeBlang concluded, "The patients who had thicker subcutaneous muscle layers were at a slightly higher risk for developing fat and muscle necrosis during the procedure that can result in focal self limiting pain in the region but were benign findings and never resulted in any serious complications." Furthermore, it was noted that patients with a thicker fat and muscle layer tended to have a lower non perfused volume in the fibroid possibly because the thicker fat layer was preventing the intensity of the beam from reaching the fibroid tissue and generating the focused heat needed to kill the fibroid. "In conclusion, patients with thicker anterior subcutaneous fat and muscle layers
are at greater risk for subcutaneous fat and muscle necrosis which results in local site pain.
No patient less than 23.5 mm thickness had subcutaneous fat/muscle necrosis. These patients tend to have lower NPV’s resulting in decreased technical successes thus the implications for candidacy issues and patient selection is important." Dr. LeBlang told MedicExchange. Fielding a question from the audience, Dr. LeBlang explained that even in cases of benign site pain, 400mg of ibuprofen has resolved the pain. (For further patient advocacy issues, refer to www.fibroidrelief.org or www.myuterinefibroids.com.)

There are several other clinical applications for MRgFUS (for further information on the technology, see: www.insightec.com.) There are currently ongoing clinical trials to treat bone pain from metastatic bone cancer. The goal of the treatment is not to ablate the tissue and eliminate the metastatic foci but actually to treat the pain that is so common in patients with bone metastasis. The patients are often dependent on narcotics to control their pain, so the goal after treatment with MRgFUS has been to show that their dependence on narcotics for pain relief is dramatically decreased to zero within a day or two after the procedure. Another application is for treatment of breast cancer, where in Japan there have been hundreds of patients treated with this technology which may obviate the need for lumpectomy or mastectomy for certain women with breast cancer. MRgFUS is also under investigation for use in prostate cancer, benign prostatic hypertrophy and targeted drug delivery.