Varian's linear accelerator used in stereotactic neurosurgery to accelerate treatment time

By E. Janene Geiss

Philadelphia, March 6 - Varian Medical Systems, Inc., said Monday that clinicians at the United Kingdom's Clatterbridge Center for Oncology have carried out their first routine stereotactic neurosurgical treatment using a Varian linear accelerator equipped with a new device for enhancing precision using 3D X-ray images.

A 40-year-old female patient with a solitary brain metastasis received a single session of radiosurgery on a Varian Clinac linear accelerator equipped with an On-Board Imager to track the exact location of the lesion, officials said in a company news release.

The On-Board Imager device enabled clinicians at Clatterbridge to pinpoint the location of the tumor using special conebeam CT images and then complete the treatment in less than an hour. Until now, this type of special treatment took up to four hours, officials said.

"The time-consuming nature of this sort of treatment has meant that we would normally have had to carry it out in the evening on specialized machines, after our routine work has been completed," Angela Heaton, research radiographer at Clatterbridge, said in the release. "It could take up to two hours to check calibrations before we could even begin treating and the whole process could take several hours, which was inconvenient for both the patient and staff and made it a relatively difficult treatment."

Stereotactic treatments could be further delayed when there was the need for neurosurgeons to attend and screw a head fixation device into the patient's skull in order to keep them in place for up to four hours. Doctors said the new imaging treatment process makes it possible to avoid this uncomfortable and time-consuming step for their patients, officials said.

Dr. Brian Haylock, the center's clinical director, said the conebeam CT capability would be extremely useful in validating the accuracy of different methods of head fixation used, which is vital in brain treatments.

"I was very impressed with the accuracy and ease of use of the On-Board Imager's CBCT imaging capability. It seemed very efficient," Haylock said in the release.

The patient selected for this pioneering treatment had previous whole brain surgery for two brain metastases from an inoperable renal tumor in August last year and although the primary tumor has not progressed, her long-term prognosis is still poor. A new 25 mm lesion had recently developed in the right fronto-parietal region of the brain and was causing the onset of facial palsy and headaches from oedema, which meant treating the lesion could greatly improve her quality of life.

Using the Clinac accelerator's 120-leaf multileaf collimator to shape a 1.5 mm beam, clinicians delivered a 15Gy stereotactic radiosurgery treatment from eight angles, carefully checking the patient's head position between each treatment field.

The entire treatment took less than an hour - about 20 minutes for patient positioning on the couch using a head-frame, two minutes for conebeam CT image acquisition, a further five minutes for online image matching and about 20 minutes for treatment delivery.

"At present we could expect to do between 10 and 12 such treatments a year," Haylock added in the news release. "These patients have previously been treated out of hours because of time constraints so this did not become routine. It's now important that we do everything we can to improve the efficiency as well as maintain treatment accuracy and improve patient comfort. That's why we want to move all our stereotactic procedures across to the Varian machine, which also has the versatility to handle routine radiotherapy treatments when it is not being used for neurosurgical cases."

Varian is a Palo Alto, Calif., supplier of equipment and software for treating cancer. The company also is a supplier of components including X-ray tubes and flat-panel detectors for medical, scientific and industrial imaging.

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