Apparatus dependence of normal brain tissue dose in stereotactic radiosurgery for multiple brain metastases

Technical note

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Technical improvements in commercially available radiosurgery platforms have made it practical to treat a large number of intracranial targets. The goal of this study was to investigate whether the dose to normal brain when planning radiosurgery to multiple targets is apparatus dependent.


The authors selected a single case involving a patient with 12 metastatic lesions widely distributed throughout the brain as visualized on contrast-enhanced CT. Target volumes and critical normal structures were delineated with Leksell Gamma Knife Perfexion software. The imaging studies including the delineated contours were digitally exported into the CyberKnife and Novalis multileaf collimator–based planning systems for treatment planning using identical target dose goals and dose-volume constraints. Subsets of target combinations (3, 6, 9, or 12 targets) were planned separately to investigate the relationship of number of targets and radiosurgery platform to the dose to normal brain.


Despite similar target dose coverage and dose to normal structures, the dose to normal brain was strongly apparatus dependent. A nonlinear increase in dose to normal brain volumes with increasing number of targets was also noted.


The dose delivered to normal brain is strongly dependent on the radiosurgery platform. How general this conclusion is and whether apparatus-dependent differences are related to differences in hardware design or differences in dose-planning algorithms deserve further investigation.

Abbreviations used in this paper: SRS = stereotactic radiosurgery; WBRT = whole-brain radiation therapy.

Article Information

Address correspondence to: Lijun Ma, Ph.D., University of California, San Francisco, 505 Parnassus Avenue, Room L-08, San Francisco, California 94143. email:

Please include this information when citing this paper: published online March 4, 2011; DOI: 10.3171/2011.1.JNS101056.

© AANS, except where prohibited by US copyright law.



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    Axial images showing target distribution.

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    Comparison of Paddick dose conformity indices for 3, 6, 9, and 12 targets. PFX = Gamma Knife Perfexion; CK = CyberKnife; NOV = Novalis.

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    Semilogarithmic plots of normal brain isodose volumes versus dose for Gamma Knife Perfexion (A), CyberKnife (B), and Novalis (C). The numbers on the upper and lower curves are the absolute total target volumes for Gamma Knife Perfexion and CyberKnife for 4, 8, 12, 16, and 20 Gy, respectively. N = number of targets.

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    Apparatus dependence of normal brain isodose volumes for multitarget treatment plans with 3 (A), 6 (B), 9 (C), and 12 (D) targets. The numbers on the curves are the normalized total target volumes for Perfexion and CyberKnife for 4, 8, 12, 16, and 20 Gy, respectively.


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