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Image-Guided Radiation Improves Outcomes in Obese Prostate Cancer Patients
September 16, 2009
Moderately to severely obese prostate cancer patients have superior outcomes when treated with top-of-the-line image-guided radiation scanners, rather than with traditional external beam radiation--or even with image-guided scanners that do not provide clear images, says Dr. James Wong, chairman of the oncology department at Morristown Memorial Hospital in Morristown, NJ.
This is because top-of-the-line scanners can easily correct for the daily movements of the prostate gland, he tells DOTmed News. These prostate movements are especially pronounced in obese individuals, since the skin overlying their lower abdomen "moves around easily" from day to day and is not always stationary when they lie down for radiation, Dr. Wong says.
He notes that a 5-foot, 11-inch male who is mildly obese weighs 210 to 250 pounds. A moderately to severely obese male, who is 5 foot 11 inches, weighs more than 250 pounds.
There are many types of image-guided machines, such as ultrasound or X-ray machines, used at cancer centers around the country, he says. With image guidance, doctors are able to compare the earlier images with those taken before each treatment session to adjust the dose if necessary.
"But the top of the line machines that use a real diagnostic CT scanner in the treatment room, such as the ones manufactured by Siemens and Varian, are only used at about 10 cancer centers in the U.S.," he tells DOTmed.
The machines are not practical for some hospitals because the set up requiring real diagnostic in-room CT scanners does not fit into conventional radiation treatment rooms, he says.
"To use these machines, the treatment room and the linear accelerator have to be completely reconfigured. This is not an easy task, especially in view of the current health care economic environment," Dr. Wong says. Just as important, most hospitals don't have top-of-the-line, state-of-the-art equipment since it's still prohibitively expensive.
He says he's optimistic that as technology improves and prices drop, more cancer centers will buy systems that take superior images.
"If it were my relative's prostate gland being irradiated, I'd want him to have the best image-guided radiation therapy available," he says.
Dr. Wong recalls that more than a decade ago, he and his colleague, Dr. Minoru Uematsu, who practices in Japan, began asking themselves whether their radiation beam was hitting the target correctly. These questions lead them to approach Siemens, which agreed to manufacture the first "CT-on-rails in-room CT" for image guidance.
At that time, he says, many cancer centers used ultrasound to determine a patient's internal anatomy prior to radiation. Dr. Wong remembers that he and Dr. Uematsu persuaded Siemens to make a system that provided precise imaging by joking, "Look at a neonatal ultrasound. Sometimes you can't even tell if its a boy or a girl."
He asked Siemens' decision-makers to make a machine that hooked up a diagnostic CT scanner to a linear accelerator.
Leaving Cornell Medical Center
In 1997, Dr. Wong was an oncologist at the prestigious New York Hospital, Cornell Medical Center. Cornell didn't have a large enough room for the machine. When Morristown Memorial Hospital told Dr. Wong they would build him the facilities he needed, he left Cornell for a community-based hospital in Morristown, which he says unlike Cornell, is not a teaching hospital.
Left to Right Shifts Are Significantly Greater in the Obese
Incidentally, he says that in 2006, a paper was published from M.D. Anderson concluding that obese people are more likely to fail external beam radiation for some "intrinsic" reason. But Dr. Wong knew differently.
"The Anderson article prompted our team to review all their patients' histories, to prove that obese men may not be receiving adequate prostate cancer treatment," he says. "We found that the percentage of moderately to severely obese patients with a left to right shift of greater than 10 millimeters was 21.2 percent compared to a 1.3 percent shift for slimmer men.
His paper was published in the September 1 issue of the International Journal of Radiation Oncology, Biology, Physics, ASTRO's official journal.
"The implications of our findings apply to various types of cancer," Dr. Wong concludes. "If patients are obese, skin localization is not good and image-guided radiation therapy is highly recommended."
Sources: ASTRO, DOTmed.com News