Feature | October 06, 2009 | Eric M. Horwitz, M.D.

GPS for the Body Targets Prostate

Radiation oncologists use new tracking technology to more precisely target prostate cancer.


Prostate cancer is the second leading cause of cancer death for men after lung cancer. The American Cancer Society estimates that 29,412 men died from prostate cancer in 2008. However, most experts agree that prostate cancer is treatable and highly curable if the disease is detected early.
A common treatment option for prostate cancer is radiation therapy, which is as effective in treating the disease as surgical removal of the prostate. Although men who are treated with radiation can have side effects, including urinary and bowel frequency and urgency and fatigue, they do not have to worry about the risks of surgery — including urinary incontinence and bleeding — and radiation treatments do not require hospitalization. In fact, most men are able to enjoy their normal daily activities during treatment.
Tracking Organ Motion
One of the biggest challenges doctors face in delivering high doses of radiation to the prostate is controlling natural internal organ motion. Clinical studies have documented that prostate organ motion is both unpredictable and variable, based on breathing and bladder and bowel filling. Each day, the prostate can shift more than 1 centimeter in some directions. During treatment, it may shift several millimeters as the patient breathes or coughs. Conventional methods to localize the prostate, including daily external ultrasound and CT imaging, do not allow for continuous monitoring of the tumor’s position in real time and cannot predict organ motion.
Organ movement is a natural and commonly occurring bodily function. However, if the target (the prostate) can be effectively tracked during treatment, the radiation can more effectively be delivered. Knowing the exact location of the target, in real time, maximizes treatment benefits and minimizes potential damage to nearby tissues or organs, which limits side effects. Tracking the target allows the physician to confidently treat a smaller volume with higher doses of radiation.
Several leading hospitals throughout the country, including Fox Chase Cancer Center in Philadelphia, Penn., have adopted technologies for tracking tumor motion. One such technology is called “GPS for the Body.” This system, developed by Calypso Medical, specifically tracks the prostate motion in prostate cancer patients, enabling physicians to detect the slightest organ movement in real time and the direction of the radiation if the prostate moves more than expected. The prostate motion is tracked based on the signals from three electromagnetic beacon transponders, each the size of a grain of rice, which are permanently implanted within the patient’s prostate gland. The transponders send benign radio waves that allow physicians to precisely pinpoint the location of the prostate, even as it moves during treatment. If necessary, the physician can pause treatment and readjust the patient, thereby minimizing or avoiding potential damage to the nearby rectum and bladder.
Current methods for aligning treatment involve imaging the tumor – using implanted gold markers and X-ray images or ultrasound scans – before each radiation session. The Calypso System provides continuous real-time positioning; akin to having a video versus having a snapshot of the tumor. In a strategic development agreement with Varian Medical Systems, the Calypso System will integrate with Varian’s radiotherapy treatment for delivering intensity-modulated radiotherapy (IMRT) and VMAT with RapidArc. The hope is the combined systems will prove beneficial for prostate patients as well as some of the more difficult radiation therapy targets such as the pancreas and lung.
Studies indicate that up to 20 percent of prostatectomy patients are diagnosed with recurrent prostate cancer following surgery and require adjuvant or salvage radiation therapy. When treating the prostate, every millimeter matters. Tracking organ motion ensures that the radiation beam hits its target — and nothing else — for the duration of treatment. Both patients who have undergone radiation using the Calypso or other tracking systems find comfort in knowing that the chances of eradicating early-stage prostate cancer is potentially increased when radiation is delivered with extra precision. Patients are relieved that side effects may be minimized and quality-of-life factors, such as bladder control and sexual function, may be preserved, enabling a faster recovery. <
About the Author
Dr. Eric Horwitz is Acting Chairman of Radiation Oncology at Fox Chase Cancer Center in Philadelphia, Penn. For more information, please call 215-728-3815. For information on Fox Chase Cancer Center, visit: www.fccc.edu.

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