Quality assurance for the Leksell gamma unit: Considering magnetic resonance image‐distortion and delineation failure in the targeting of the internal auditory canal

Abstract

Our aim in this study was to distinguish quantitatively between the localization accuracy of a commercially available stereotactic fixation device as claimed by the manufacturer and the target accuracy as measured by a user, applying neuroradiologic imaging in Gamma Knife planning and phantom irradiation. Missing the target is the most serious possible failure in Gamma Knife and Linac therapy. To reduce this risk, we developed a quality control algorithm and designed a phantom. To evaluate the accuracy of the targeting procedure with a Leksell Gamma unit, and to experience the possible errors in all procedural steps, irradiations of phantoms were performed, using the so-called "unknown" targeting method. Accuracy is defined by the extent of spatial deviation of the irradiated target from the calculated target. Digital imaging was used for therapy planning. GafChromic films, which had been irradiated while affixed to a specially developed phantom, were used for measuring the precision of the radiation unit. A series of MR images (in two plains: transverse and coronal) was acquired sequentially to image the three-dimensional (3-D) volume of the phantom. The results obtained for isocentric accuracy of the Leksell Gamma unit, model B, were in good agreement to the calculated position. The observed spatial deviations between calculated and irradiated targets is less than 1 mm. The newly designed phantom and quality control algorithm are useful in quality assurance measurements of stereotactic radiation therapy.

Clinical Evaluation of Stereotactic Target Localization Using 3-Tesla MRI for Radiosurgery Planning

“…In SRS, much effort has been invested in determining the spatial integrity and validity of standard (1.5T) MRI for image guidance (16)(17)(18)(19)(20). Because 1.5T constitutes the standard of care, it can serve as a spatial reference that should be maintained with increasing field strength.…”

Quality assurance in stereotactic space. A system test for verifying the accuracy of aim in radiosurgery

“…Along with the other imaging devices, the MRI scanner is conceived as part of this radiosurgery system. Because of potential localization errors due to spatial distortions, 10 the MR image data have been checked against stereotactic projection images as a reference. This paper describes the method and results of the complete or global system test meaning to quantify how precise a given target can be treated with the radiosurgical system based on MRI.…”

Accuracy and stability of positioning in radiosurgery: Long term results of the Gamma Knife system

“…Only in a few papers has an approach to the overall uncertainty deriving from image distortions, target localization and definition, dose calculation, biological model, patient positioning, and last but not least the mechanical accuracy of the system, been described. Ertl et al 8 used the so-called unknown targeting method to show the spatial deviation between irradiated tar- get and calculated target. Meeks et al 9 verified calculated dose distributions with BANG gel-dosimetry, whereas Rosenzweig et al 10 stressed quality assurance for every step in the chain.…”