Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2017 Mar;18(2):37-43.
doi: 10.1002/acm2.12044. Epub 2017 Feb 2.

The spatial accuracy of two frameless, linear accelerator-based systems for single-isocenter, multitarget cranial radiosurgery

Gary A Ezzell  1
Affiliations

The spatial accuracy of two frameless, linear accelerator-based systems for single-isocenter, multitarget cranial radiosurgery

Gary A Ezzell. J Appl Clin Med Phys. 2017 Mar.

Abstract

Single-isocenter, multitarget cranial stereotactic radiosurgery (SRS) is more efficient than using an isocenter for each target, but spatial positioning uncertainties can be magnified at locations away from the isocenter. This study reports on the spatial accuracy of two frameless, linac-based SRS systems for multitarget, single-isocenter SRS as a function of distance from the isocenter. One system uses the ExacTrac platform for image guidance and the other localizes with cone beam computed tomography (CBCT). For each platform, a phantom with 12 target BBs distributed up to 13.8 cm from the isocenter was aligned starting from five different initial offsets and then imaged with the treatment beam at seven different gantry and couch angles. The distribution of the resulting positioning errors demonstrated the value of adding a 1-mm PTV margin for targets up to about 7-8 cm from the isocenter. For distances 10 cm or more, the CBCT-based alignment remained within 1.1 mm while the ExacTrac-based alignment differed by up to 2.2 mm.

Keywords: margins; multitarget; single-isocenter; stereotactic radiosurgery.

PubMed Disclaimer

Figures

Figure 1
Figure 1
Photograph of the “Blockhead” phantom (a), anterior MV radiograph (b), and lateral MV radiograph (c). Target T0 is at the center. In the anterior radiograph, targets T1–T6 run top to bottom, targets T7–T9 are on the image right, top to bottom, and targets T10–T11 are on the image left, top to bottom.
Figure 2
Figure 2
Example alignment image on the ExacTrac system (a) and on the CBCT system (b). The planned image is in the spyglass window in each.
Figure 3
Figure 3
The average and maximum offsets (in mm) between the planned and imaged targets along with the average plus two standard deviations as a function of distance from the isocenter (in cm): (a) for the iX with ExacTrac and (b) for the TrueBeam with CBCT.
Figure 4
Figure 4
The 95% confidence limits, approximated by the average offset plus two standard deviations, for the two platforms plotted on a single graph.
See this image and copyright information in PMC

References

    1. Nichol A, Ma R, Hsu F, et al. Volumetric radiosurgery for 1 to 10 brain metastases: a multicenter, single‐arm, phase 2 study. Int J Radiat Oncol Biol Phys. 2016; 94:312–321. - PubMed
    1. Clark GM, Popple RA, Prendergast BM, et al. Plan quality and treatment planning technique for single isocenter cranial radiosurgery with volumetric modulated arc therapy. Pract Radiat Oncol. 2012;2:306–313. - PubMed
    1. Clark GM, Popple RA, Young PE, Fiveash JB. Feasibility of single‐isocenter volumetric modulated arc radiosurgery for treatment of multiple brain metastases. Int J Radiat Oncol Biol Phys. 2010;76:296–302. - PubMed
    1. Wolff HA, Wagner DM, Christiansen H, Hess CF, Vorwerk H. Single fraction radiosurgery using RapidArc for treatment of intracranial targets. Radiat Oncol. 2010;5:77. - PMC - PubMed
    1. Mayo CS, Ding L, Addesa A, Kadish S, Fitzgerald TJ, Moser R. Initial experience with volumetric IMRT (RapidArc) for intracranial stereotactic radiosurgery. Int J Radiat Oncol Biol Phys. 2010;78:1457–1466. - PubMed

MeSH terms

LinkOut - more resources