Sounding Out Tumors
Porter Advances Promising Noninvasive Cancer Treatment
By Mark Dwortzan
Processed images showing thermal destruction achieved in tissue-mimicking hydrogel with (left) and without (right) the presence of microbubbles during 7.5-second high-intensity ultrasound exposure. Thermal destruction turns the hydrogel from black to white in the images, which occurred more quickly when microbubbles were formed via vaporization.
Treatment options for solid, cancerous tumors include surgery, radiation and chemotherapy, but all three involve lengthy recovery times and damage healthy tissue and the immune system. Over the past five years, Associate Professor Tyrone Porter (ME, BME) has advanced a technique that combines nanotechnology and focused ultrasound for tumor destruction while avoiding the harmful side effects associated with conventional treatment methods.
Developed in collaboration with Nathan McDannold, research director of the Brigham and Women’s Hospital/ Harvard Medical School Focused Ultrasound Laboratory, the technique is to inject nontoxic liquid perfluorocarbon nanodroplets into the bloodstream where they accumulate in solid tumors over time. High intensity focused ultrasound (HIFU) pulses are then used to vaporize the nanodroplets within the tumor. The process yields microbubbles that boost tissue absorption of ultrasound, producing sufficient heat to kill the tumors in less time than when using HIFU alone.
Using tissue-mimicking hydrogels as a model for solid tumors in an article published recently in Journal of Therapeutic Ultrasound, Porter has shown that microbubble-enhanced HIFU can destroy solid tumors using 70 percent less acoustic power while reducing the ultrasound exposure time by at least 50 percent when compared to conventional HIFU.
“This results in less risk of skin burns because you’re using much less energy, dramatically cuts down the time for treating larger tumors, and makes it possible to treat tumors in organs protected by bone such as the ribcage or skull,” said Porter.
Building on these results and funded by a new four-year, $1.8 million grant from the National Institutes of Health, Porter and McDannold are now investigating whether their technique can be used to destroy tumors in the kidneys, which are partially protected by the ribcage and therefore more difficult to treat with ultrasound.
Because bone would absorb some of the ultrasound, treatment time would increase. In addition, connective tissue at the bone surface could be damaged by heat from the ultrasound. By sharply reducing the power and time needed to destroy cancer tumors in the kidney and other organs protected by bone, the researchers aim to make ultrasound a viable option for treating hard-to-reach solid tumors.
“Ultrasound for destroying tumors is not widely accepted in the U.S.,” said Porter. “I’m hopeful that our work will lead to wider acceptance of using ultrasound to treat solid tumors and provide a new treatment option for inoperable cancers.”
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