Device Detects Small Movements During Radiation Treatment For Prostate Cancer

Radiation for prostate cancer treatment involves targeting intense beams in a very precise fashion to a relatively small area. But despite efforts to align a patient beforehand, a cough, a wiggle, adeep breath or any other number of small movements could dramaticallyalter where the treatment is being delivered.

To help eliminate the error associated with treating a moving target, the University of Michigan ,, s Radiation Oncology department has begun using a new system designed to detect in real time the location of a tumor. The system, called the Calypso 4D Localization System, will be used within the U-M Comprehensive Cancer Center to guide treatment during external beam radiation therapy for prostate cancer. U-M is the first cancer center in Michigan to purchase the device and one of a few cancer centers in country involved in the clinical study evaluated by the U.S. Food and Drug Administration.

"During the treatment, if there ,, s any change in the prostate ,, s location, we ,, ll know instantly and can correct the treatment. We know these movements occur, but presently we have no way of detecting them during the treatment, says Howard Sandler, M.D., professor of radiation oncology and urology at the U-M Medical School.

With the new Calypso System, radiation oncologists implant three small electromagnetic sensors, about the size of a grain of rice, into a patient ,, s prostate. The sensor is a passive device until it is coupled with the Calypso System during treatment. The sensor is implanted in a simple outpatient procedure, similar to a biopsy.

Currently, doctors implant gold seeds in the prostate, which show up on X-rays to mark where the radiation needs to be delivered. But the X-rays represent the prostate ,, s location only at the moment in which they were taken. If the patient coughs or takes a deep breath, the prostate could move.

The Calypso System and the implanted transponders generate electromagnetic signals that tell the radiation therapist when the tumor target is perfectly aligned. A computer system allows the therapist to monitor in real time where the prostate is, noting if it moves outside the area targeted to receive radiation. If it moves outside that zone, the therapist can stop the treatment and either wait until the prostate moves back or reposition the patient.

Typically, patients who receive radiation are carefully positioned on the table, at times using restraints around the ankles to prevent leg or pelvis movement. Small tattoos and laser guide lights help a technician align the patient in a consistent location. One-third of the treatment session can involve positioning the patient.

Once positioned, patients typically have X-rays taken to show where the prostate is sitting. From day to day, a prostate tumor can move more than one centimeter " a big difference when pinpoint beams of radiation are being delivered. The Calypso System eliminates the need for X-rays, exposing patients to less ionizing radiation and removing one more step out of the daily radiation therapy process. Prostate cancer patients can receive radiation daily for six to eight weeks.

U-M was among the first centers to test the Calypso System in an FDA clinical study, enrolling 10 patients. The device will now also be used as part of a research protocol. Calypso Medical currently has clearance from the FDA only for prostate cancer, although U-M radiation oncologists hope to study the device in other cancer types as well.

More than 1.2 million Americans a year receive radiation treatment for cancer. According to the American Cancer Society, 218,890 men will be diagnosed with prostate cancer this year and 27,050 will die from the disease.