Physicists, physicians, engineers photograph radiation beams through the Cherenkov effect
January 20, 2014
A scientific breakthrough may give the field of radiation oncology new tools to increase the precision and safety of radiation treatment in cancer patients by helping doctors “see” the powerful beams of a linear accelerator as they enter or exit the body.
We don't have X-ray vision. When we have an X-ray or mammogram, we cannot detect the radiation beam that passes through our bone or soft tissue, neither can our doctor. But what if we could see X-rays? When we use powerful X-rays for cancer treatment, we could see how they hit the tumor. If we were off target, we could stop and make adjustments to improve accuracy. Pinpoint precision is important. The goal of radiation is to kill cancer cells without harming healthy tissue.
Safety in Radiation Oncology
As a way to make radiation safer and better, Dartmouth began to investigate a scientific phenomenon called the Cherenkov effect in 2011. Our scientists and engineers theorized that by using Cherenkov emissions the beam of radiation could be "visible" to the treatment team. The ability to capture an X-ray would show:
- how the radiation signals travel through the body
- the dose of radiation to the skin
- any errors in dosage.
TV viewers may have seen images of sunken fuel rods from a nuclear power plant emitting a blue-green glow. That is the Cherenkov effect. When a particle with an electric charge travels faster than the speed of light through something that does not conduct electricity, like the human body or water, it glows. As the matter relaxes from polarization, it emits light. (Yes, for a brief period people glow during radiation.)
The Cherenkov effect in the laboratory
As a first step, engineers at Thayer School of Engineering at Dartmouth modified a regular camera with a night vision scope to take photos of radiation beams as they passed through water. What appeared on the photos is the Cherenkov effect, a luminescent blue glow. Dartmouth engineering student, Adam Glaser [in Professor Brian Pogue's lab], explains how it works in this video:
To refine the approach for use in radiation treatment, scientists used a mannequin of the human body. They measured and studied the results to refine their ability to capture the luminescence, experimenting with beam size, position, and wavelength.
Cherenkov imaging used for first time in treatment setting
With the clinical aspects refined, Geisel School of Medicine researchers photographed luminescence during the routine radiation treatment of a dog with an oral tumor. (Read "The Power of Small Cures" to learn more about the dog's care.)
This was the first time Cherenkov studies came out of the laboratory and into a treatment setting. The scientists coined the approach Cherenkoscopy. As they anticipated, during the session they were able to see detailed information about the treatment field and the dose. The results were published in the November 2013 issue of the Journal of Biomedical Optics.