Getting the right dose.
The colored contours indicate the intensity of the IMRT radiation: the tumor bed (red) gets the most, chest (orange) receives less, and heart (green) and other areas that also receive little can [
Jinsheng Li / Fox Chase Cancer Center
Radiation is heavy artillery against tumors: It can clear the cancer cells, but the surrounding tissues often suffers damage collaterals. Now a group of researchers has developed a new technique that calculates the path the radiation takes, may allow oncologists to target tumors more precisely.
therapeutic radiation usually involves X-ray shot by beams or electron tumor. At the base, the beam is rectangular in cross section. Tumors tend to be lumpy and do not conform to simple geometries, however, and the parts of the beam miss the tumor can damage healthy cells.
Recently, a technique called intensity modulated radiation therapy (IMRT) has helped doctors zap the tumor while sparing the flesh. The technique divides the rectangular beam into many small beams. Each sub-beam can be tuned to a different energy; stronger if the tumor is deep or thick in this location, lower if the tumor is thin. A second beam can shine simultaneously from another direction. When the two beams intersect, the power is increased. This composite beam can be precisely adjusted to cover the entire tumor.
Control of the beams is not easy, however. X-rays and electrons do not follow predictable paths through the body, and they interact with unpredictably tissue, making it difficult to calculate exactly how much radiation is zapping the tumor compared to wreak havoc elsewhere. For better precision, physicists Jinsheng Li and Chang-Ming Ma at Fox Chase Cancer Center in Philadelphia, Pennsylvania, developed a fast computer program specific to simulate billions of trips of each beam of radiation through a map patient's body. The program then analyzes the data statistically and reads "best bet" beam design, which a radiation oncologist can use to configure the equipment.
Not only the new, more accurate technique, but it's faster too. Previous programs have taken days to calculate a single radiation dose. Li and Ma program can do calculations in an hour. The team will present its findings, August 1st at the American Association of Physicists in Medicine meeting in Orlando, Florida.
What is exciting about the technique is that it is sufficient to treat tumors anywhere in the body flexible, said Eric Klein, a physicist in radiation oncology at Washington University School of Medicine in St. Louis , Missouri. But he warns that the modulated radiotherapy for electrons has not been approved by the Food and Drug Administration, or combined x-ray / electron IMRT, and it may take 3 to 4 years before the approach of the team used in the clinic.
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