J Korean Neurosurg Soc.  2023 Jul;66(4):476-481. 10.3340/jkns.2022.0164.

Avoiding a Collision in Gamma Knife Radiosurgery : A Modified Mask Fixation Method

• Moon HC
• Lee D
• Min BJ
• Kim YG
• Dho YS

• KMID: 2543539
• DOI: http://doi.org/10.3340/jkns.2022.0164

Abstract

Objective
: The latest version of the Leksell Gamma Knife IconTM allows for mask- and frame-based fixation. Although mask fixation provides fractionated treatment and immobilization using a noninvasive method, it is not free from collision. The authors investigated the collision problem with a modified mask fixation method.
Methods
: This study presents a case of two meningiomas in the frontal area, where a collision occurs in the occipital area. A modified mask fixation method was introduced to avoid the collision : first, the edges of the head cushion were cut off and polystyrene beads with a diameter of approximately 5 cm were removed. Next, the head cushion was sealed using a stapler. Finally, the head cushion was flattened in the adapter. We compared the shot coordinates, 3-dimensional (3D) error, clearance distance, and vertical depth of the head cushion between the initial and modified mask fixations.
Results
: When comparing the initial and modified mask fixations, the difference in the shot coordinates was +10.5 mm along the y-axis, the difference in the 3D error was approximately 18 mm, and the difference in clearance was -10.2 mm. The head cushion was approximately 8 mm deeper in the modified mask fixation.
Conclusion
: Based on these findings, we recommend a modified mask fixation method for gamma knife radiosurgery using ICON with a collision.

Keyword

Collision; Modified mask fixation method; Head cushion; Gamma knife radiosurgery; Meningioma

Figure

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  Fig. 1. The Leksell GammaPlan showed the unreachable position for both shots in the right frontal falx. The yellow circle indicates the treatment dose of 13 Gy shot isocenter (50% isodose). Snapshot view of gamma knife dose planning on the axial plane (A), sagittal plane (B), and clearance (C).

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  Fig. 2. Production of a modified mask fixation when a collision occurs. Cut the edges of the head cushion (A), pull out polystyrene beads about 5 cm in width, 5 cm in length, and 4 cm in height from head cushion (B), sutured with stapler (C).

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  Fig. 3. Comparison of the vertical length of the initial and modified mask fixation. Vertical depth of the initial head cushion is about 4 cm (A). Vertical depth of the modified head cushion of about 4.8 cm (B). The red arrow indicates a ruler.

Reference

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