The study also examined dose interplay - the additional dose delivered to the normal brain surrounding each target as consequence of irradiating the other targets. According to Dr. Ma, the non-coplanar geometry of Gamma Knife radiosurgery beam delivery helps significantly limit dose interplay effects in comparison to linac-based modalities, particularly as the number of targets increases.

The area in which Perfexion had a significant disadvantage compared to TrueBeam was length of beam-on time, with Perfexion producing the longest beam-on time of 50-148 minutes. TrueBeam yielded the shortest beam-on time of six to nine minutes.


"Although Perfexion had a longer beam-on time than all the other modalities, the frame-based nature of Gamma Knife radiosurgery greatly reduces patient set-up time and treatment planning time can also be significantly shorter," Dr. Ma says. "In addition, physics and quality assurance work plus treatment planning effort also can be significantly less."

"Dr. Ma and his group have demonstrated very definitively that Gamma Knife is unparalleled in its ability to treat multiple brain metastases with the greatest conformity and the least amount of dose scatter to the normal brain," adds Dheerendra Prasad, MD, Medical Director, Department of Radiation Medicine at Roswell Park Cancer Institute (Buffalo, New York). "In our own experience at Roswell of just the last 75 patients and a total of 272 brain tumors, it was possible to spare 98 percent of normal brain tissue with Gamma Knife Perfexion. Any time gained in treatment with other modalities including the flattening filter-free techniques is outweighed by the loss of selectivity of these other methods. Gamma Knife continues to be the gold standard for radiosurgery, both for benign and malignant tumors and the only real contender for radiosurgery of functional disorders."

Ma L, Petti P, Wang B, et al. (2011) Apparatus dependence of normal brain tissue dose in stereotactic radiosurgery for multiple brain metastases. J Neurosurg 114(6):1580-1584. doi:10.3171/2011.1.JNS101056
Ma L, Nichol A, Hossain S, et al. (2014) Variable dose interplay effects across radiosurgical apparatus in treating multiple brain metastases. Int J CARS. Published online: 20 April 2014. doi:10.1007/s11548-014-1001-4
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Gert van Santen, Group Vice President Corporate Communications, Elekta AB
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Raven Canzeri, Global Public Relations Manager, Elekta

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