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Proton tracking

Researchers at the University of Florida (Gainesville, FL) have come up with a new take on proton-therapy dose verification: imaging gamma ray emission during the treatment process. The distribution of gamma rays - produced when high-energy protons interact with nuclei in the patient’s tissue - provides a measure of the location and amount of energy delivered during treatment.

"If we have a way to image gamma rays, we can almost do real-time dose verification," said researcher Yuxin Feng, speaking at an AAPM session entitled Innovative frontiers in medical physics.

To detect the gamma rays, Feng and colleagues designed a Compton camera based on LaBr₃, a new scintillation material with high stopping power and good energy resolution. They used pixellated LaBr₃ crystals for both the camera’s scattering and absorbing detectors.

The crystal modules in the front (scattering) layer are 2.5x2.5x0.5 cm in size, segmented into 4x4x2 mm on the surface to enhance spatial resolution. The detectors in the rear layer are 2.5x2.5x3.0 cm, segmented into 4x4x10 mm.

"The prototype Compton camera is able to image gamma rays from 0.5 to 2 MeV," said Feng. He noted that this technique could also be used to monitor high-energy photon-based therapies.

The proposed Compton camera offers a potential angular resolution of about 0.3 radians when imaging 511 keV gamma rays, and 0.05 radians or less for gamma rays above 2 MeV. Bench-top tests demonstrated a spatial resolution of 5 mm (at 662 keV) - sufficient to detect the distal fall-off of a proton beam.

Feng says that the Florida team now plans to test the prototype camera in clinical radiotherapy facilities, using both proton and photon beams.

Also in the pipeline: new configurations, such as dense scattering cameras or multiple cameras with a perpendicular set-up; and acceleration of the camera’s 3D image reconstruction speed. Ultimately, it’s this fast image reconstruction that could make real-time imaging of proton therapy a reality.
 

Posted by Tami Freeman on July 29, 2008 11:18 PM | Permalink