Researchers Construct Computer Simulations of Laser-Nanoparticle Treatments

Yildiz Bayazitoglu, a professor of mechanical engineering from Rice University (Houston, TX, USA) and a specialist on heat transfer and fluid flow, and doctoral student Jerry Vera are using computer simulations to quantify the effect of heating nanoparticles with near-infrared lasers to destroy cancer tumors without damaging healthy tissue.

The investigators hope to increase the effectiveness of destroying tumors by modifying methods of heating them based on the size and composition of not only the tumor but also the surrounding tissue. The study was published in the January 2009 issue of the International Journal of Heat and Mass Transfer.

The researchers revealed that attacking a tumor with two lasers could heat it more thoroughly than a single laser. For tumors as large as 1 cm, simulations showed opposing lasers surgically inserted via fiberoptics in a minimally invasive procedure generated the most uniform temperature profile in every case.

Lasers and nanoparticles are already being used to treat cancer. A company founded by Rice scientists Drs. Jennifer West and Naomi Halas, Nanospectra Biosciences, Inc. (Houston, TX, USA), is conducting human tests of a system that uses nanoshells heated by near-infrared lasers to kill tumors. Drs. Bayazitoglu, West, and Halas are all part of Rice's Laboratory for Nanophotonics.

The Bayazitoglu group's approach would refine such treatment by taking into account the light-scattering properties of nanoparticles. Their concern is that nanoparticles near the surface of a tumor will block a laser from reaching those at the center. "Think about it this way: If you're driving on a very foggy night, you can only see just so far no matter how good your headlights are,” commented Dr. Vera. "That's because the millions of small water droplets in the air absorb and scatter the light, deflecting the beams from your headlights before they can reflect off of whatever's ahead of you on the road. Nanoparticles dispersed within a tumor do exactly the same thing. They're very good at absorbing laser light and generating heat, but within particularly thick tumors, that same quality prevents a lot of the light from reaching deeper into the tissue.”

Dr. Bayazitoglu reported that this phenomenon, called "extinction,” is "highly undesirable.” A uniform temperature profile of at least 60 ^oC has to be created to kill the whole tumor. "Raising the temperature on one end but not the other will simply allow the tumor to regrow, and that doesn't solve the problem--or cure the patient.”

The density and placement of nanoparticles in the tumor are critical, according to Dr. Bayazitoglu. "Ideally, you should put nanoparticles at the center of the tumor, then kill it from the center out,” Dr. Bayazitoglu said.

Laser treatment may be effective even if nanoparticles are not used, she noted. "If the tumor has good absorption properties, slow heating can do a good job of killing the cancer, because the heat has time to get inside. If you're doing that, sometimes it's better not to use nanoparticles.”

With so many tissue types and the great range of cancers people face, the importance of accurate simulations cannot be overemphasized, according to the researchers. They hope the ability to calculate scenarios will allow clinicians to find the best laser therapy to produce the perfect heating environment.

Related Links:
Rice University
Nanospectra Biosciences