Protons In The War On Cancer
Proton therapy -- which uses beams of the subatomic particles to treat cancer -- is a hot topic at this year's American Association of Physicists in Medicine (AAPM) meeting, which takes place from July 26 - 30 in Anaheim, CA. Ways to make the technology more effective, cheaper, and smaller will be discussed, and news of research on proton computed tomography (proton CT) -- which uses protons to image the body's interior -- will be unveiled to a wide audience for the first time.
The reason proton beams are better for some types of cancer than other therapeutic forms of radiation, such as X-rays, is that well-aimed energetic protons deposit more of their energy inside cancerous tissue and less in neighboring healthy tissue. This happens because protons, unlike X-rays, surrender much of their energy near the place where they come to rest, which can be deliberately aimed to fall within a tumor.
Included below are highlights of a few of the presentations related to proton therapy.
PROTON FACILITIES ARE EXPANDING
X-rays continue to be the main method of treating tumors with beams of energy. But proton facilities are becoming more common. Worldwide, says Alfred R. Smith of the M.D. Anderson Cancer Center in Houston, there are more than 25 medical institutions with proton machines, and 25 more are in the planning or construction stages. More than 55,000 people have been treated with protons so far.
Smith will provide an overview of the current status of proton therapy. He will also discuss the use of beams of carbon ions, parcels consisting of 16 protons and neutrons bound together, which might be even more effective in killing cancer cells than individual protons -- though the apparatus needed is more elaborate and expensive than for protons. The talk "Proton Physics and Technology" is at 8:05 a.m. on Monday, July 27 in Ballroom B). More information: http://www.aapm.org/meetings/09AM/PRAbs.asp?mid=42&aid=11866.
LASER DRIVEN PROTONS
In general, machines that accelerate protons for cancer therapy are larger and much more costly than X-ray machines. For some cases, such as treatment for children, in which the collateral damage caused by X-rays would be unacceptable, the higher cost of protons is justifiable. Still, researchers have tried to invent new, more economical means of producing proton beams, either by streamlining the traditional method of accelerating protons using high voltage or by using laser light.
Dale Litzenberg, a scientist who studies radiation oncology at the University of Michigan, will report on his group's efforts to accelerate protons by bombarding a thin foil with light from a 300-terawatt laser. The electric fields within the short laser pulses cause a "coulomb explosion" in the foil, liberating protons and other particles. Litzenberg will describe efforts to sculpt the laser pulse to generate protons useful for cancer therapy. The goal is to obtain a tenfold reduction in the cost of delivering therapeutic protons. The poster "Experimental Implementation of the Directed Coulomb Explosion Regime of Laser-Proton Acceleration" is at 4:00 p.m. on Monday, July 27 in Exhibit Hall - Area 2. More information: http://www.aapm.org/meetings/09AM/PRAbs.asp?mid=42&aid=11748
In a separate talk on a related subject, Charlie Ma from Fox Chase Cancer Center in Philadelphia will discuss "Laser-Driven Targetry: The Road to Clinical Applications" at 2:10 p.m. on Monday, July 27 in Ballroom D. More information: http://www.aapm.org/meetings/09AM/PRAbs.asp?mid=42&aid=11988
George Caporaso and his colleagues at Lawrence Livermore National Laboratory are attempting to bring down the cost of proton therapy by bringing down the size of the apparatus. They hope to produce a proton source for treatment that could fit in a single X-ray machine-sized vault. The talk "Dielectric Wall Accelerators for Proton Therapy" is at 1:50 p.m. on Monday, July 27 in Ballroom D. More information: http://www.aapm.org/meetings/09AM/PRAbs.asp?mid=42&aid=11987.
PROTON COMPUTED TOMOGRAPHY
Protons can also be used for tomographic imaging -- visualizing the inside of the body by piecing together cross-sectional images. Reinhard W. Schulte of the Loma Linda University Medical Center in Loma Linda, California will describe proton computed tomography, or pCT for short, a process in which a beam of protons is passed through the body. By comparing the energy of each proton going in to its energy coming out, Schulte can reconstruct an accurate map of the body's interior that includes tumors.
The technology is similar to current CT scanners that use X-rays. However, while X-ray CT measures the attenuation of multiple photons, pCT detects energy loss from single protons, so a lower dose of energy could achieve the desired effect. Computer studies suggest that pCT scanning would require from 2 times to 10 times less dose to produce an image of similar resolution. Sub-millimeter resolution can be attained for head-sized objects, and millimeter resolution can be attained in other parts of the body. The pCT enterprise is still at an early stage of development and involves not only building the machines and detectors but also developing advanced computer algorithms for extracting images from the measured data. Some first experimental pCT images as well as simulated images will be shown at the meeting. The talk "A Status Update On the Development of Proton CT at Loma Linda University Medical Center" is at 2:06 p.m. on Thursday, July 30 in Ballroom C). More information: http://www.aapm.org/meetings/09AM/PRAbs.asp?mid=42&aid=10533.
Benjamin Fahimian of John DeMarco's lab at the University of California, Los Angeles will talk about the possible use of anti-protons -- the antimatter counterparts of protons -- in cancer therapy. Why go to the trouble of producing beams of antiprotons, created in high-energy collisions of protons with a special target? Because, says co-author Michael Holzscheiter, the antiprotons might deposit as much as four times more dose per particle than protons. The team will be reporting on the development of a new treatment planning system for antiproton therapy and the study of collateral energy deposited around the antiproton trajectory. So far only cell cultures have been targeted, and the advantages of antiprotons have yet to be verified with actual tumors.
The talk, "Antiproton Radiotherapy: Development of Physically and Biologically Optimized Monte Carlo Treatment Planning Systems for Intensity and Energy Modulated Delivery" is at 11:00 a.m. on Wednesday, July 29 in Ballroom B. More information: http://www.aapm.org/meetings/09AM/PRAbs.asp?mid=42&aid=11422.
Main Meeting Web site: http://www.aapm.org/meetings/09AM/.
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Meeting program: http://www.aapm.org/meetings/09AM/MeetingProgram.asp.
American Institute of Physics