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Jefferson Takes Lead in Real-Time Imaging with Radiation Therapy

A patient’s diagnostic, radiation-treatment planning CT scan with one of his daily cone beam scans. This is used to fine-tune the daily treatment and assess contour changes in the patient’s tumor and organs.

It’s a matter of millimeters.

While one of the Holy Grails in radiation oncology is to spare as much healthy tissue as possible during therapy, patients undergoing treatment for weeks at a time physically change. For all the meticulous treatment planning that goes into pinpointing radiation to the tumor site, the fact is, radiation treatment itself can be taxing. During a period of therapy, for example, patients might lose weight, lose or gain fluid, and tumors may shrink or, unfortunately, continue to grow. As a result, radiation target sites change, which can be problematic for treatment and raises treatment questions.

“Do you collect treatment data, study them and look for patterns of variation, and every few weeks make an adjustment in the radiation therapy based on them, or do you make an adjustment daily?” asks Walter J. Curran Jr., MD, Professor and Chair of Radiation Oncology at Jefferson Medical College of Thomas Jefferson University and Thomas Jefferson University Hospital and Clinical Director of the Kimmel Cancer Center at Jefferson.

New technology seeks answers
Jefferson is one of the first centers in the nation to study the effect of incorporating a new technology – cone beam CT (computed tomography) – into a source of radiation, namely a linear accelerator machine, in an attempt to find an answer to this vexing problem. The technology creates three-dimensional axial CT slices of a patient’s tumor (i.e., around the axis of the tumor), enabling therapists and doctors to compare these images with initial treatment planning images to determine how precisely focused the radiation set-up is. They can then make position adjustments if necessary to deliver a more targeted therapy to the patient. The hope is that this technology will lead to more highly customized radiation treatments, where higher doses are directed at the tumor while sparing the patient’s normal body structures.

"Right now, cone beam is being used as one additional means of verifying the accuracy of the radiation treatments that we deliver,” says Mitchell Machtay, MD, the Walter J. Curran Jr., MD, Associate Professor of Radiation Oncology at Jefferson Medical College and Vice Chair of the Department of Radiation Oncology.

Traditionally, patients are positioned for their daily radiation treatment by making marks on the patient’s skin, based on earlier tests, says Dr. Machtay. “Once that is done, unless dramatic changes are seen, it’s hoped that those marks will hold up for two or three or six weeks of radiation and that the treatment will be given accurately.

Left to right, Jefferson radiation oncologists Richard Valicenti, MD, Walter J. Curran Jr., MD, and Mitchell Machtay, MD.

“Ultimately, we believe that cone beam will lead to more highly customized radiation treatments, such as higher doses to the gross tumor and lower doses to normal structures within the body,” explains Dr. Machtay, who specializes in treating head and neck cancers. Such tumors can be tightly packed together with critical normal structures.

Richard Valicenti, MD, Associate Professor and Clinical Director of the Department of Radiation Oncology at Jefferson Medical College, uses cone beam CT for treatment planning for patients with prostate cancer. “We’ve never had a way to directly visualize a target for radiation therapy before,” he notes.

“Cone beam is a potential paradigm shift in checking the accuracy of a treatment.” says Dr. Machtay.

How cone beam works
In cone beam CT, the CT scanner is physically attached to a radiation delivery machine. Prior to the actual treatment, a set of three-dimensional CT scan images is obtained. This is 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 given.

“Positioning no longer depends on the road map marks on the skin,” says Dr. Machtay. “With cone beam, we are actually looking at a CT scan of the inside of the patient to see if he or she is lined up properly and if there’s been a change in the size or shape of the individual.

“We’re using it to collect quality assurance data, to see how much movement there is from the first day of treatment to every other day of treatment. We’re making the measurements and the adjustments necessary to hit the tumor.

“What we haven’t done as yet is actually change the number of radiation treatments, the dosages of treatment or the size of the beams based on the CT scans,” he notes. In theory, cone beam is more accurate and the radiation beams can be more pinpointed, meaning less radiation exposure to the rest of the patient. That can mean fewer side effects, and perhaps a higher dose of radiation.

In treatment planning for head and neck cancer radiation therapy, Dr. Machtay explains that at least a 5-millimeter safety margin around the cancer is typical. “If this margin is reduced to 2.5 mm, and we think of it three-dimensionally, that’s a lot less area of radiation exposure.”

Cone beam, he notes, can be applied to any cancer type. Dr. Machtay says that clinical trials using cone beam radiation are in the planning stages.

“It’s something that we would consider state of the art but not yet standard of care,” he says. Dr. Machtay notes that the device is not yet approved by the FDA, but currently is only used on about 25 percent of the patients receiving radiotherapy at Jefferson Hospital.

Jefferson is the most experienced center in the Delaware Valley in using cone beam technology, Dr. Curran notes. It’s been operational for about eight months.

For more information about Jefferson's Radiation Oncology Department, call 215-955-6702 or 1-800-JEFF-NOW , or visit us online at www.JeffersonHospital.org/radonc