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Monday, March 3, 2014

A weird glow in nuclear power plants is proving valuable when aiming cancer treatment

David Brooks

Ever seen a picture of a nuclear power plant, with the water around reactors glowing an eerie blue? That’s due to something called Cherenkov radiation, a release of energy when charged particles pass through material with such force and speed that it sort of exceeds the speed of light in that material.

Turns out, we humans emit Cherenkov radiation when hit with X-rays during cancer treatment. The energy output is tiny so we’re not exactly Dr. Manhattan, the aquamarine dude from Watchman comics, but there is a glow, and it carries information. ...

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Ever seen a picture of a nuclear power plant, with the water around reactors glowing an eerie blue? That’s due to something called Cherenkov radiation, a release of energy when charged particles pass through material with such force and speed that it sort of exceeds the speed of light in that material.

Turns out, we humans emit Cherenkov radiation when hit with X-rays during cancer treatment. The energy output is tiny so we’re not exactly Dr. Manhattan, the aquamarine dude from Watchman comics, but there is a glow, and it carries information.

Now some folks at Dartmouth College think they can help doctors make use of that information.

“There are so many people involved in radiation therapy, and it’s all done with computer simulations. ... The radiation therapist doesn’t have their hands around all that,” said Brian Pogue, who is a professor of engineering, of physics and of surgery (yes, surgery) at Dartmouth and its medical and engineering schools. “This gives them a real, tangible visualization of what is happening.”

X-rays and other charged particles are emitted by a linear accelerators and focused on tumors to kill them. Radiation can damage healthy cells of course, so precise dosage and aim is vital. The idea of the Dartmouth researchers is to use cameras to visualize the faint Cherenkov radiation, improving treatment and reducing side effects such as skin reactions.

Sounds obvious and easy, but not so.

“The problem is that the (Cherenkov radiation) is many orders of magnitude less intense than normal room lighting,” said David Gladstone of Norris Cotton Cancer Center, where he is chief of Clinical Physics. (What a title to put on your business card: There’s way more overlap between medicine and physics than I ever realized.)

Gladstone and his team, including Ph.D. students, took up the problem after Pogue mentioned the idea of allowing therapists to somehow visualize Cherenkov radiation. Eventually they realized that the trick is to take pictures only when the linear accelerator is actually firing, which happens in bursts that are 3 millionths of a second long, occurring every 10 thousands of a second.

That’s a non-trivial precision to achieve, but it cuts the signal-to-noise ratio down to manageable levels, said Gladstone. It also takes some non-trivial equipment: The scientific camera with an image intensifier costs around $65,000, Gladstone said, although that’s not much of an addition to a linear accelerator that costs at least $3 million.

The teams have gone through equipment test to make sure they could actually detect the emission in a clinical setting with the beams from commercial cancer treatment units, then did animal tests and are winding up a trial with 10 breast cancer patients, to correlate what they see with what happens to patients. The best part is that the technology doesn’t interfere with existing practices.

“There’s actually no change to the standard treatment techniques. It’s practically free information once you get the system in place,” said Gladstone. Lots of details need to be worked out, of course: “We’re still doing development work to find optimal geometric conditions for mounting in room, whether inside the accelerator gantry itself, rotate about the patient, or how to do it best.”

Dartmouth holds some patents, Gladstone said, but “We’re taking a pure academic tack right now. ... We don’t have any vested interested in forming a company, per se.”

The group will be presenting their findings at scientific conferences, “hoping that other people will start investigating as well. Debate is always healthy with many minds involved.”

“The medical community has to decide whether this an acceptable incremental cost and what the benefit is,” he added.

From the point of view of a science fanboy, I really like the way this discovery grew from a bit of informed serendipity. Pogue got the idea of visualizing Cherenkov radiation during treatment while attending a Royal Society scientific conference in England, after seeing a presentation from a group researching light detection from nuclear medicine, which is a wildly unrelated topic.

“Dr Pogue’s field is optics ... and he goes these optics conferences. That’s pretty far removed from day-to-day cancer treatment,” said Gladstone.

So is he surprised at the way it has progressed?

No at all, he said: “That’s the way science is supposed to work.”

GraniteGeek appears Mondays in The Telegraph. David Brooks can be reached at 594-6531 or dbrooks@nashuatelegraph.com. Follow Brooks on Twitter @granitegeek.