Cooking Cancer With Gold Nanoshells

Computationally modeling the hot spots

Tiny gold particles that absorb laser light and convert it into heat are a promising therapy for destroying tumors. However, controlling the temperature of such gold nanoshells is crucial: The shells must get hot enough to kill tumor cells, but they must not scorch nearby healthy tissue. Now, researchers have developed a model that predicts how much these nanoshells raise the temperature of surrounding tissue.

 

Cross-sectional view of the temperature dis- tribution in a tissue-like medium filled with gold nanoshells after three minutes of near- infrared laser treatment. Only the bottom layer of the medium (starting at a 12 mm depth) contains gold nanoshells. Reprinted with permission from Medical Physics 36(10), 4665, 2009. doi:10.1118/1.3215536 (2009).“When we tried to estimate how much heat is being generated from the process, we didn’t have any good way to quantify it,” says Sang Hyun Cho, PhD, a medical physicist at the Georgia Institute of Technology and senior author of the study in the October 2009 issue of Medical Physics. With the new model, researchers won’t need to directly measure temperature with invasive temperature probes or magnetic resonance thermometry imaging, Cho says.

 

Other teams have modeled the temperatures of nanoshells in tissue. However, their models assumed that the nanoparticles spread out evenly, Cho says. “But we know that gold nanoshells are not uniformly distributed in tissue,” he observes. Instead, the particles cluster tightly in some tumor regions and avoid others. That’s because nanoshells travel to the growths within a tangle of misshapen blood vessels, but the vessels don’t reach all parts of the tumor.

 

Using basic heat transfer principles, Cho’s group created a computational model to calculate the heat generated by individual shells. At first, Cho assumed the nanoshells spread out evenly. But, unlike previous efforts, Cho’s model is well-suited to capture the pattern of hot spots arising from a more realistic nanoshell distribution, he says.

 

The simulations captured the general heating profiles from past experiments but, Cho says, couldn’t match the exact temperatures—probably because the team lacked good measurements of how much light is absorbed and scattered at the wavelength they used, thus affecting their calculations of the conversion to heat. His group plans experiments to pin down these values.

 

“They are doing very theoretically well-founded simulations,” says David Paik, PhD, professor of radiology at Stanford University. The next important step is modeling heating in a more realistic nanoshell distribution, he says. “This is where their more computational approach would be a big win.”
 



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