Using Microbubbles with High-Intensity Ultrasound Enhances Cancer Therapy

Microbubbles have been shown to decrease the acoustic strength and time of ultrasound scanning that is required to heat and destroy an embedded target. If these new findings can be validated in clinical practice, microbubbles could improve the effectiveness of high-intensity ultrasound treatment of solid tumors.

The study’s findings were published April 2013 in BioMed Central’s new open access Journal of Therapeutic Ultrasound. High-intensity ultrasound is already utilized to treat solid tumors. Ultrasound can be focused through soft tissue and, because it does not require probes or surgery, is noninvasive. However, if the tumor is behind the skull or ribcage, the bone absorbs some of the ultrasound. The length of treatment, consequently, needs to be increased, moreover, there is a potential for heat damage to the bone.

To optimize ultrasound therapy, especially in these difficult to treat cases, investigators from Boston University (MA, USA), has developed phase-shift nanoemulsions (PSNEs), which produce tiny microbubbles when blasted with high-intensity ultrasound. Microbubbles smaller than 200 nm passively accumulate in tumors and these findings reveal that microbubbles of this size can intensify the effects of ultrasound in hydrogels designed to mimic solid tumors inside the body.

Holes formed in a predictable manner and with a predictable shape, which altered with acoustic intensity. The acoustic intensity and exposure time required for thermal destruction of tumor tissue were both reduced by more than half, compared to ultrasound without microbubbles. The lower power levels and time needed to destroy a target in the presence of microbubbles could potentially improve cancer therapy, especially in hard to reach areas.

The first phase in any new treatment is to show safety and efficacy. Prof. Tyrone Porter, from the mechanical engineering department at Boston University (MA, USA), who led this study, explained, “We used PSNE [phase-shift nanoemulsions] of phospholipid coated perfluorcarbon which have no known toxicity and have already be shown to be safe clinically. Our technique pushes forward the possible applications of ultrasound therapy in treating solid tumors.”

“Focused ultrasound technology has enormous potential to improve the quality of lives for millions around the world,” noted Neal F. Kassell, MD, chairman and founder of the Focused Ultrasound Foundation. “The research reported in the Journal of Therapeutic Ultrasound will be central to advancing the field and will help accelerate the progress of focused ultrasound towards clinical adoption.”

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