An Evaluation of the Accuracy of Magnetic-Resonance-Guided Gamma Knife Surgery

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We used a spherical phantom to evaluate geometric accuracy in multi-platform stereotactic neuroimaging for radiosurgery. The phantom consisted of two plastic 16-cm-diameter hemispheres in which an exchangeable 8-cm plastic functional cube was incorporated. The functional cube contained cylinder and point targets. The targets were filled with a mixed aqueous solution of 2-mM copper sulfate and 300-mg/ml iodinated contrast medium and were visible on both MR and X-ray images. Two MR scanners and a biplane X-ray angio-suite were used to scan the phantom stereotactically in two sessions of the experiment. The angio-suite was equipped with digital subtraction and distortion-correction software. The resulting stereotactic images were transferred to a dose-planning computer for length measurement and coordinate determination of the targets. The mean errors of the measured cylinder length on distortion non-corrected X-ray stereotactic images were 0.24 ± 0.14 and 0.73 ± 0.10 mm, respectively, in the experiments; on distortion-corrected images 0.22 ± 0.10 and 0.35 ± 0.39 mm. They were 0.50 ± 0.24, 0.25 ± 0.19 and 0.49 ± 0.34, 0.23 ± 0.25 mm, respectively, of the two MR scanners. The mean errors of coordinate determination of point targets between the stereotactic MR and the distortion-corrected X-ray images were 0.70 ± 0.18, 0.52 ± 0.22 and 0.76 ± 0.25, 0.40 ± 0.10 mm, respectively, in the experiments. We found that the overall geometric errors of target delineation between stereotactic MR and X-ray images were in the submillimeter range. The current study validates the multi-platform and multi-facility stereotactic neuroimaging practice and ensures imaging accuracy in radiosurgery.

Section: Discussionsupporting

confidence: 56%

Section: Discussionmentioning

confidence: 82%

Section: Discussionmentioning

confidence: 99%

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Evaluating Geometric Accuracy of Multi-Platform Stereotactic Neuroimaging in Radiosurgery

Wu¹,

Lee²,

et al. 2002

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“…The MR image clearly demonstrates the contour of the brain tumor in the sellar and juxtasellar region as well as the critical structures, such as optic nerves, optic chiasm, and optic tract, on transaxial, coronal and sagittal images. Although CT scanning has been considered as the gold standard in terms of imaging distortion, modern MR scanners minimize distortion by improvement in homogeneity of the magnetic field [7,8]. In addition, the image is regularly calibrated for linearity of magnetic homogeneity every two weeks in our institution.…”

Section: Discussionmentioning

confidence: 99%

Protection of Visual Pathway in Gamma Knife Radiosurgery for Craniopharyngiomas

Chung

Pan

Guo³

et al. 1998

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Craniopharyngiomas present a major challenge to Gamma Knife radiosurgery (GKRS) due to their proximity to the optic apparatus. Based on observations of the evolving tumoral change on MRI and clinical results, an optimization of the treatment strategy and dose selection is possible. From March 1993 to September 1996, 21 patients with craniopharyngiomas were treated by GKRS. Every patient received stereotactic MRI exclusively for targeting and dose planning. The tumor and adjacent structures, including optic nerves, chiasm, and tracts were carefully identified and delineated on sagittal, coronal and axial films. The tumor volume ranged from 0.3 to 28 ml (average 9 ml). We purposefully apply multiple isocenters (average 9.1 shots) to create an isodose curve that covered the tumor optimally while sparing the optic pathway. The marginal dose prescribed was 9.5 to 16 Gy (50%). The maximal dose was 19 to 32 Gy. The maximal dose to the optic apparatus was 3.2 to 12.5 Gy. After GKRS, all patients were followed up clinically every month. MR studies were conducted every six months with the same techniques on the same scanner to investigate evolution of tumor volume and any adverse radiation effect. The follow-up period ranged from 6 to 40 months (mean: 18.4, median: 19). All patients were followed more than 6 months. Nineteen out of 21 cases (90.5%) achieved tumor control; that is, 18 tumor shrinkage (volume reduction: 15–95%) and 1 stabilized tumor growth. Among these 21 patients, 7 had improved visual acuity or visual field after GKRS, and the rest remained stable. Two patients developed mild T₂ change on MRI without any endocrinological disturbance or visual impairment. Protection of the visual pathway can be secured by a sophisticated delineation on 3-dimensional stereotactic images with multiple-shot dose planning. Craniopharyngiomas with tumor volume up to 25 ml were treated safely and effectively, because the dose to the optic apparatus was kept as low as possiby this strategy. Further follow-up is needed to determine the highest tolerable dose to surrounding critical structures and the long-term outcome of tumor control.

“…As is well known, several factors contribute to data errors, including imaging distortion, delineation errors in tumor margins, morphology of tumors, computed slices in each tumor, and size of tumors [5][6][7][8] . In this study, we calculated the volume by the Gamma Knife workstation as the basis for determining the data errors from the PACS (product of surface area and thickness of slices) and geometric methods.…”

Section: Introductionmentioning

confidence: 99%

Prediction of Volumetric Data Errors in Patients Treated with Gamma Knife Radiosurgery

Pan¹,

Cheng

Sun³

et al. 2007

Purpose: Volumetry is the most commonly used method to measure tumor response in patients who receive Gamma Knife radiosurgery. We calculated the data errors in measurement made by different methods based on the stereotactic fiducials (Gamma Knife workstation), surface area multiplied by thickness (PACS), and product of maximum diameter in x, y, and z dimensions (geometric method) to more precisely evaluate tumor response in patients treated with Gamma Knife radiosurgery. Materials and Methods: From 2003 to 2006, 210 tumors were enrolled in this study. MRIs obtained from these patients were transferred to Gamma Knife and PACS workstations. Data errors were defined as the difference between the volume calculated by various methods and the Gamma Knife workstation divided by the volume obtained from the Gamma Knife workstation. Linear regression was used for data analysis. Results: There were 27 lesions with volume <0.5 cm³, 97 lesions between 0.5 and 4 cm³, 68 lesions between 4 and 14 cm³, and 18 lesions larger than 14 cm³. A strong linear correlation was found between the volume measurement by Gamma Knife workstation and PACS and the geometric method (r = 0.993, 0.967, respectively). Poor correlation between the Gamma Knife and PACS workstation volume measurement was observed in tumors less than 0.5 cm³ (r = 0.763), but better correlation was found between the Gamma Knife workstation and geometric method (r = 0.871). Fewer data errors were observed in the PACS than in the geometric method (p < 0.001) in tumors with volumes of 0.5–4 cm³ and 4–14 cm³; whereas in tumors less than 0.5 cm³, fewer data errors were observed in the geometric method (p = 0.01). The data error in the whole series was 6 ± 15% in the PACS system and was relatively correlated with the volume (p = 0.03) and the number of slices (p = 0.021), but not with the Pearsonian coefficient of skewness (p = 0.81). Conclusion: The different methods of measurement of tumor volume (>0.5 cm³) demonstrated strong linear correlation. In tumors with volume less than 0.5 cm³, the most reliable method was the geometric method. When using the PACS system in the evaluation of tumor response, a data error as high as 21% should be considered.