Uterine fibroids (leiomyomas) are a common cause of heavy uterine bleeding and pain in reproductive aged women and are the most common cause of hysterectomy in the United States. Women are seeking new ways to treat symptomatic uterine fibroids that allow them to avoid surgery. This study is the first step in this quest. We will study the novel use of magnetic resonance imaging (MRI) in enhancing the safety of the FDA approved technique to treat fibroids called High Intensity Focused Ultrasound (HIFU). The term high intensity focused ultrasound means using ultrasound to heat and to thermally destroy tissue, in this case, uterine fibroids. The MRI system will allow us to watch the ultrasound path during treatment and monitor the temperature increase in the fibroid tissue that comes during the procedure. Similar to existing HIFU systems, the Philips system enables ablation of uterine fibroids under MR image guidance. However, the Philips system adds two unique features to existing MR guided HIFU therapy, which have the potential to reduce treatment times and improve safety compared to existing MR guided HIFU systems. These are the use of volumetric ablation and automated thermal feedback. Volumetric heating refers to the use of a rotating focal spot, which is moved electronically in a circular path with a fixed radius at high speed. This enables heating of larger zones or cells in one sonication compared with point by point sonication used by existing HIFU systems. Point by point sonication delivers HIFU using a fixed focal spot that moves in a pre-determined raster or grid layout of treatment cells arranged in rows and columns. During volumetric sonication, the transducer applies heat in a continuous circular manner to adjacent points within the treatment cell. These treatment cells, with diameters of 4, 8, or 12 mm, are placed within a target treatment area to make up the planned treatment volume (PTV). Treatment is performed by stepping through several treatment cell ablations with cooling times between each sonication. Each HIFU volumetric cell ablation is performed with an ultrasound power level set to achieve a tissue heating of 50 70C. The duration of the exposures are linked with the cell size, and are fixed by the system. Volumetric treatment allows for complete and uniform cell coverage, with the potential to reduce treatment time compared to existing MR guided HIFU systems. In animal experiments comparing the use of volumetric ablation to rastered, or point by point sonication, volumetric sonication has been shown to have treatment speeds up to 7 times faster with the use of the 12 mm volumetric cell than with the use of a single point ablation of the same size. The Philips HIFU system also allows volumetric heating to be performed with automated thermal feedback. When automated thermal feedback is enabled, the duration of sonication will be limited by the measured thermal dose in the cell, as detected by MR thermometry. For example, if optimal thermal dose as measured by MR is reached prior to 20 seconds in the case of a 4-mm treatment cell, the sonication is stopped by the system software, preventing tissue overheating. Existing MR guided HIFU systems rely entirely on the operators detection of elevated thermal doses in order to stop the treatment. The use of automated thermal feedback has the added benefit of ensuring delivery of optimal thermal dose and improving safety by minimizing the risk of overheating and thus overtreatment. In this pilot study, women with symptomatic fibroids will undergo MRI guided HIFU and then have a hysterectomy. This will allow us to confirm studies done in animals which show that it is possible to destroy specific tissue without harming normal tissue surrounding the targeted area.
|Venkatesan, Aradhana M; Partanen, Ari; Pulanic, Tajana Klepac et al. (2012) Magnetic resonance imaging-guided volumetric ablation of symptomatic leiomyomata: correlation of imaging with histology. J Vasc Interv Radiol 23:786-794.e4|