Videogame processors reduce radiation in image guided radiation
26 July 2010
A new approach to processing X-ray data could lower by a
factor of ten or more the amount of radiation patients receive during
cone beam CT scans, report researchers from the University of
California, San Diego.
Cone beam CT plays an essential role in image-guided radiation
therapy (IGRT), a state-of-the-art cancer treatment. IGRT uses
repeated scans during a course of radiation therapy to precisely
target tumours and minimize radiation damage in surrounding tissue.
Though IGRT has improved outcomes, the large cumulative radiation
dose from the repeated scans has raised concerns among physicians
Reducing the total number of X-ray projections and the electric
current level per projection (by tuning down the X-ray generator
pulse rate, pulse duration and/or current) during a CT scan can help
minimize patient's exposure to radiation, but the change results in
noisy, mathematically incomplete data that takes hours to process
using the current iterative reconstruction approaches. Because CBCT
is mainly used for treatment setup while patients are in the
treatment position, fast reconstruction is a requirement, explains
lead author Xun Jia, a UCSD postdoctoral fellow.
Based on recent advances in the field of compressed sensing, Jia
and his colleagues developed an innovative CT reconstruction
algorithm for graphic processing unit (GPU) platforms. The GPU
processes data in parallel — increasing computational efficiency and
making it possible to reconstruct a cone beam CT scan in about two
minutes. Modern GPU cards were originally designed to power 3D
computer graphics, especially for video games.
With only 20 to 40 total number of X-ray projections and 0.1 mAs
per projection, the team achieved images clear enough for
image-guided radiation therapy. The reconstruction time ranged from
77 to 130 seconds on an NVIDIA Tesla C1060 GPU card, depending on
the number of projections — an estimated 100 times faster than
similar iterative reconstruction approaches, says Jia.
Compared to the currently widely used scanning protocol of about
360 projections with 0.4 mAs per projection, Jia says the new
processing method resulted in 36 to 72 times less radiation exposure
"With our technique, we can reconstruct cone beam CT images with
only a few projections — 40 in most cases — and lower mAs levels,"
he says. "This considerably lowered the radiation dose."
The reconstruction algorithm is part of the UCSD group's effort
to develop a series of GPU-based low dose technologies for CT scans.
"In my mind, the most interesting and compelling possibilities of
this technique are beyond cancer radiotherapy," says Steve Jiang,
senior author of the study and a UCSD associate professor of
"CT dose has become a major concern of the medical community. For
each year's use of today's scanning technology, the resulting
cancers could cause about 14,500 deaths.
"Our work, when extended from cancer radiotherapy to general
diagnostic imaging, may provide a unique solution to solve this
problem by reducing the CT dose per scan by a factor of 10 or more,"