Surgical Probe Uses Fluorescence to Guide Brain Tumor Removal
February 4, 2013
A team from Thayer School of Engineering and Dartmouth-Hitchcock Medical Center is among the first to harness fluorescence to prevent tissue damage during brain surgery.
Over a decade ago, a group of German doctors discovered that if a patient is given an oral dose of a 5-aminolevulinic acid solution before brain surgery, a chemical reaction will cause certain cells, including cancer cells, to appear fluorescent, allowing them to identify tumors for removal during surgery.
But it was Dartmouth engineering professor Keith Paulsen and his team, along with doctors from the Ontario Cancer Institute in Toronto, who took even more of the guesswork out of fluorescence-guided brain surgery by creating a fiber optic probe that when placed on early-stage, low-grade tumors detects fluorescence not visible to the naked eye.
Since 2008, about 100 clinical case studies by Dartmouth Hitchcock’s Chief Neurosurgeon Dr. David Roberts have shown that samples removed from the brain under the probe after patients consumed the solution were indeed cancerous, sharpening the accuracy of the solution from 64 to 94 percent. Paulsen, also a member of the Cancer Imaging and Radiobiology Research Program at Norris Cotton Cancer Center, hopes that using the probe to analyze physical qualities of tumors to make cancer tissue glow like lava will become the FDA-approved standard of practice a within a few years.
“The bulk of the brain will not absorb the drug, which means that anything that glows is a tumor,” says Dartmouth engineering Ph.D. student Kolbein Kolste, who in addition to leading future development of the probe helped design a camera system that attaches to a microscope, working like the probe for the whole surgical field instead of just a single point. “The probe comes into play when the level of fluorescence is below what the eye can detect, so a surgeon can remove only the cancerous brain tissue.”
Until recently, brain tumor removal was left to educated guesses based on preoperative MRIs that are outdated once the surgery begins because tissues sway, swell and sag. In most other cancers, a surgeon will remove tissue surrounding malignant tumors to err on the side of caution. However, when cancer cells living in the brain are removed, that extra tissue cannot be taken out for fear of brain damage, and the precision of each cut is even more critical because cancerous and ordinary tissue appear identical.
The probe’s ability to provide surgeons with instant feedback makes surgery more efficient and effective and safer, despite the fact that using fluorescent light for brain surgery isn’t curative. Controlled by a computer that runs a sequence for exciting the fluorescence and collecting light, the probe has a highly sensitive spectrometer that splits light up into its various colors, measuring how much of each wavelength is present and allowing algorithms to differentiate between low levels of fluorescent light and background light. This four-inch long small bundle of fibers has a metal tip at one end and hooks into a box of light sources and the spectrometer on the other end.
Dartmouth is the first to create a clinical probe to detect low levels of fluorescence, but surgeons are using fluorescence, for example, by attaching fluorescent chemicals to proteins that are taken up by ovarian cancer cells, causing them to glow.
“Some tissues will fluoresce without a tumor, and some tumors may not fluoresce, so it will not be useful in all cases. However, we are confident that the probe could be used in even more tumor types, guiding surgery for other tricky tumor resections,” says Kolste. “Surgeons are enthusiastic that they have a powerful tool that can give real-time feedback in the decision making process of tumor resection.”