RapidArc, Varian’s technology for delivering volumetric modulated arc therapy (VMAT), enables clinicians to deliver a highly-precise image-guided intensity-modulated treatment quickly, often with just one revolution of the treatment machine around the patient.

“We found that we can deliver RapidArc treatments much more quickly, with an average of 76% less beam on time, and also using 31% fewer monitor units, which could limit unintended and undesired radiation exposure to patients,” said Daniel C. Schiffner, M.D., chief resident in the UCI Department of Radiation Oncology, in a presentation at the annual meeting of the American Society for Radiation Oncology (ASTRO) in Chicago.

“The reduction in monitor units is important because it limits the degree to which patients are exposed to radiation leakage from the treatment machine,” he said. “In addition, less ‘beam on’ time improves our clinical workflow, improves patient comfort during treatment, and limits the potential for patient and organ motion during the treatment session, which can allow more accurate dose targeting.”

In addition to being faster and requiring fewer monitor units, RapidArc treatments were found to conform to the shape and size of a targeted tumor at least as well as dynamic, fixed-beam approaches to IMRT, SRS, and SRT. “Treatment with RapidArc VMAT using a single arc produced similar dose conformality and homogeneity compared with earlier, more time-consuming approaches,” said Schiffner.

Since 2008, clinicians at UC Irvine have been using Varian’s Trilogy medical linear accelerator to treat tumors with either SRS or SRT, using a dynamic form of IMRT delivered from multiple beam angles. The department acquired RapidArc technology in early 2009, “permitting us to treat complex targets with a single arc,” Schiffner said. “The technology makes it possible to dynamically shape the beam, and at the same time vary the dose delivery rate and the speed of rotation around the patient. By varying those elements, RapidArc achieves the significant time savings.”

Schiffner and a team of colleagues reported on a study that compared the two treatment approaches for a total of eight patients with a total of 13 lesions.

“All of the RapidArc plans were delivered in a single arc, while IMRT plans required 7-14 fields for delivery,” said Schiffner. “The clinically important advantages we saw lead us to recommend the use of image-guided RapidArc to optimize the delivery of SRS and SBRT for intracranial and extracranial targets.”