Symmetry helps radiation oncologists at Riverside & University of Virginia Radiosurgery Center avoid excess dose to healthy tissues by isolating mobile tumors

In treatments of only the first handful of patients with lung or liver tumors, Riverside & University of Virginia Radiosurgery Center (Newport News, Va.) clinicians have demonstrated the dramatic benefit that Elekta’s Symmetry™ 4D image guidance technology can provide for patients whose tumors move with their breathing. Symmetry essentially yields a more distinct picture of the tumor, without the blurring associated with breathing motion.

By having a clearer picture of the tumor position and its motion, physicians have been able to improve their targeting of tumors, thereby avoiding having to treat a larger margin of healthy tissue around the lesion. A Symmetry scan is acquired just before treatment to ensure that the patient is correctly positioned, and to visualize tumor movement.

“Symmetry scans give us clearer information about the movement of the tumor, allowing us to increase the safety of treating our patients by decreasing the dose to healthy tissues, while hopefully providing a better clinical outcome,” according to Riverside medical physicist Kelly Spencer.

Tumor motion in sharper focus

Before they began using the Symmetry feature in Elekta’s XVI package of IGRT tools, Riverside clinicians were using sophisticated XVI 3D cone beam CT (VolumeView™ CBCT) imaging technology integrated with their Elekta Synergy® S to image tumors. These pre-treatment scans provide physicians with added confidence in the margins that they have planned. Although seeing a target with IGRT technology such as VolumeView has been a key clinical improvement, the motion still created a blur that encompassed the tumor’s range of motion.

“For our current protocol, we would create an ITV [internal target volume] to cover the blur we see on the VolumeView,” Spencer says. “We began using Symmetry on a couple of patients with lower lung lesions near the diaphragm where we would expect tumor motion to be an issue. We were actually quite mesmerized by the images Symmetry provided. We could clearly see the actual motion of the delineated tumor with respect to the patient’s breathing.”

The same Symmetry benefit applied to a recent patient with a liver tumor situated near the diaphragm. In this case, clinicians inferred tumor motion by observing the movement of the liver with the patient’s breathing.

“We wanted to use Symmetry to see how the superior border of the liver moved, and what we observed was that it did not move simply superior to inferior – there was almost a rolling pattern to the liver motion,” Spencer recalls. “We knew that the liver didn’t necessarily move symmetrically on CBCT scans, but it was harder to appreciate due to motion artifact. This movement probably varies between patients, so that is an excellent reason to use Symmetry to evaluate this motion on a case-by-case basis.”

Read more at: http://www.elekta.com/healthcare_international_press_release_20071329.php.

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