Stereotactic Treatment of Tumors Potentially Exposes Patients to Less Radiation

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 November 2009 at the annual meeting of the American Society for Radiation Oncology (ASTRO) in Chicago, IL, USA. "The reduction in monitor units is important because it limits the degree to which patients are exposed to radiation leakage from the treatment machine. 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 intensity-modulated radiotherapy (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 Dr. 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,” Dr. 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.”

Dr. Schiffner and a team of colleagues reported on a study that compared the two treatment approaches for eight patients with 13 lesions. "All of the RapidArc plans were delivered in a single arc, while IMRT plans required 7-14 fields for delivery,” said Dr. 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.”

Varian Medical Systems is a world-leading manufacturer of medical devices and software for treating cancer and other medical conditions with radiotherapy, radiosurgery, proton therapy, and brachytherapy. The company supplies informatics software for managing cancer clinics, radiotherapy centers, and medical oncology practices. Varian is a key supplier of tubes and digital detectors for X-ray imaging in medical, scientific, and industrial applications and also supplies X-ray imaging products for cargo screening and industrial inspection.

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University of California, Irvine Medical Center
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