Cone Beam CT Improves Treatment Accuracy

While one of the most important goals in radiation is to spare as much healthy tissue as possible during treatment, patients undergoing radiotherapy for weeks at a time physically change. Patients can lose weight during a period of therapy and may lose or gain fluid. Tumors may shrink or, unfortunately, continue to grow. As a result, radiation target sites change, which can be problematic for treatment.

Thomas Jefferson University Hospital (Philadelphia, PA, USA) and the Kimmel Cancer Center at Jefferson are among the first centers in the United States to evaluate the effect of incorporating a new technology--cone beam computed tomography (CT)--into a source of radiation called a linear accelerator, to try to find a solution to this difficult dilemma.

The cone beam technology creates three-dimensional (3D) axial CT slices of a patient's tumor, enabling therapists and clinicians to compare these images with initial treatment planning images to determine how precisely focused the radiation planning is. They can then make position adjustments if needed to deliver a more targeted therapy to the patient. The potential of this technology is that it will lead to more highly tailored radiation therapy, where higher doses are directed at the tumor while sparing the patient's normal body structures.

"Right now, cone beam is used as one additional means of verifying the accuracy of the radiation treatments that we deliver,” stated Mitchell Machtay, M.D., an associate professor of radiation oncology at Jefferson Medical College of Thomas Jefferson University. Conventionally, patients are positioned for their daily radiation treatment by making marks on their skin, based on earlier tests, Dr. Machtay explained.

In cone beam technology, the CT scanner is attached to a radiation delivery unit. Prior to the actual treatment, a series of 3D CT scan images is captured and compared to the conventional CT scan that was used for planning the patient's radiation treatment. If there are any differences in the patient's current position, this is corrected before treatment is actually administered.

In theory, cone beam is more precise and the radiation beams can be more isolated, meaning less radiation exposure to the rest of the patient. That can mean fewer side effects, and possibly a higher dose of radiation. In treatment planning for head and neck cancer radiation therapy, Dr. Machtay reported that at least a 5-mm safety margin around the tumor is typical.

Cone beam can be applied to any tumor type. Moreover, while clinical trials using cone beam radiation are still in the planning stages, according to Dr. Machtay, "it's something that we would consider state of the art but not yet standard of care.” The device is not yet approved by the U.S. Food and Drug Administration (FDA) and at present is used on only approximately 25% of the patients receiving radiation therapy at Jefferson.



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