Tumor-Tracking Technology Reduces Side Effects from Radiation for Prostate Cancer

A prospective, multisite study is the first outcomes-based study to evaluate the quality of life of high-dose intensity-modulated radiotherapy (IMRT) to the prostate with tightly contoured treatment technically described as "reduced treatment margins.” The study findings demonstrate that the use of tumor tracking technology during high dose external beam radiation for prostate cancer resulted in a significant reduction in rectal and urinary treatment-related side effects.

Calypso Medical Technologies, Inc. (Seattle, WA, USA) is a developer of the targeting technology used for precise real-time tracking of tumor targets, reported the study results, published in the online in February 2010 in the journal Urology. "This is the first comparative study to show that margin reduction in prostate cancer radiation therapy has clinically significant and measurable benefits in decreasing acute toxicity and short-term side effects. By reducing acute toxicity, we hope these patients may also experience a significant reduction of long-term side effects,” said Dr. Constantine Mantz, radiation oncologist at 21st Century Oncology (Cape Coral, FL, USA) and lead investigator of the study. "When prostate cancer patients evaluate treatment options, their objective is to select the therapeutic approach that will cure the cancer while allowing them to remain as fully functional as possible. The Calypso system, which enables physicians to deliver increased doses of radiation directly to the tumor, while sparing the surrounding healthy organs from exposure, is fundamental to our overall approach of treating prostate cancer.”

Organ motion is prevalent, variable, and unpredictable during radiation therapy and can be caused by normal physiologic events such as digestion, breathing or coughing. Tracking and responding to this motion is critical for radiation treatments because internal movement of the organ and tumor increases the likelihood that the radiation beam will miss the intended target and deliver radiation to the surrounding healthy tissue, causing side effects. To ensure that the treatment target stays within the path of the radiation beam, physicians typically increase the planning treatment volume (PTV) margin, which is defined as the area of healthy tissue surrounding the prostate tumor that is exposed to the radiation beam. With real-time tracking of the target using the Calypso technology, physicians are able to decrease the PTV margins, thereby subjecting less healthy tissue to radiation, according to the investigators.

Researchers compared the AIM study group of 64 patients to 153 patients in a comparator study published in the New England Journal of Medicine (NEJM) in 2008. Beacon electromagnetic transponders, which are the size of a grain of rice and emit signals that track the location of the prostate with submillimeter accuracy, were implanted into the prostates of the AIM study group. This level of precision allowed researchers to reduce the PTV margin while at the same time increase the radiation dose to 81 Gy to more effectively treat the cancer. Comparator patients were treated using standard institutional processes and larger PTV margins.

In both groups, patient-reported quality of life was assessed before and after the completion of radiation therapy using a clinically validated questionnaire, the Expanded Prostate Cancer Index Composite (EPIC) that measures several different domains of the patient's health. Changes in scores were compared between the AIM study and comparator groups while accounting for important patient and cancer characteristics. The AIM study group experienced considerably fewer side effects associated with bowel urgency and frequency, fecal incontinence, and urinary irritation than the comparator group. AIM patients not receiving hormonal therapy also experienced smaller, yet statistically significant advantages over the comparator group in terms of sexual function.

"Without any tracking at all, I used to use a 10-mm treatment margin; with Calypso, I use a 3-mm treatment margin and the AIM study results demonstrate an improvement in patient-reported quality of life,” said Howard M. Sandler, M.D., chair of radiation oncology at Cedars-Sinai Medical Center's Samuel Oschin Comprehensive Cancer Institute (Los Angeles, CA, USA), lead author on the AIM study and investigator in the NEJM comparator study. "Of all the technologies that are available, the Calypso system is the only one that can do real-time tracking as well as localization and provides an important advantage in terms of keeping the radiation beam on the prostate.”

The Calypso system, with its GPS for the Body technology, provides real-time tumor tracking during radiation treatment. Calypso Medical's proprietary technology utilizes miniature Beacon transponders implanted in the diseased organ to provide accurate, precise, continuous information about the tumor target's position during external beam radiation therapy. The Calypso system is cleared by the U.S. Food and Drug Administration (FDA) for use in radiation therapy for the prostate and prostatic bed; however, the technology is designed for body-wide applications.

"This study validates our long-held belief that the ability to track tumor motion in real-time is a critical component in adapting radiation therapy, as it assures the clinician and the patient that radiation is delivered to the cancerous tissue while sparing healthy tissue and decreasing unwanted side effects,” said Kenneth Russell, M.D., medical director at Calypso Medical. "We are excited about these results as we move forward in expanding the reach of our technology into applications where the tumors experience higher velocity movement.”

Related Links:
Calypso Medical Technologies
21st Century Oncology