Oregon Health & Science University researchers have determined exactly how much breathing affects prostate movement during radiation treatment.
The results of this research were presented at the 50th annual American Society for Therapeutic Radiology and Oncology in Boston on September 24.*
"Many people think that the prostate is a static organ, meaning that it doesn't move in relation to the bony pelvis, but that is not the case. The prostate is a moving organ, and we know it moves because of many factors including how full other organs are, such as the bladder," said Tasha McDonald, M.D., Radiological Society of North America research resident grant recipient, OHSU Department of Radiation Medicine.
Although previous studies have demonstrated that the prostate moves during the breathing cycle, McDonald used the new image-guided Calypso Medical System because it offers "real time" tracking. It works by using tiny beacons, inserted into the prostate, that report the exact location and the motion patterns inside the body over time.
"Our research demonstrates that the prostate moves during the breathing cycle, mostly up and down, as much as 2 millimeters. We were able to determine this motion by evaluating the Calypso tracings of patients," McDonald said. The Calypso results were also verified by other radiation technology.
"This is important information because in low-risk prostate patients, we treat the prostate (and seminal vesicles) with a small margin, 5 to 7 millimeters to account for prostate motion and set-up error. By knowing all the factors that contribute to prostate motion, we will be able to determine appropriate margins. If the margins are too large, there can be more normal tissue toxicity and if too small we could miss the prostate," McDonald said.
Greater accuracy allows the delivery of higher-dose radiation, leaving healthy cells alone. This process simultaneously reduces side effects, specifically rectal and bladder toxicities, and erectile dysfunction, as well as offering patients a better chance for a cure.
*The presentation is titled, "Quantifying Respiratory-Induced Prostate Motion Using Real Time Tracking Technology."
Radiation therapy is used to treat approximately 1 million cancer patients in the United States each year. It is one of the most effective cancer therapies. Each year, 218,000 men are diagnosed with prostate cancer, according to the American Cancer Society. In prostate cancer treatment the most common side effects arise when the radiation beam misses the prostate but irradiates adjacent healthy organs, causing complications like impotence, urinary incontinence and rectal bleeding. Therefore, doctors must guard against damaging healthy tissues that surround the tumor caused by misalignment and unpredictable tumor motion.
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