J Korean Neurosurg Soc.  2021 Jan;64(1):13-22. 10.3340/jkns.2020.0186.

Validation of Gamma Knife Perfexion Dose Profile Distribution by a Modified Variable Ellipsoid Modeling Technique

• Hur BI
• Jin SJ
• Kim GR
• Kwak JH
• Kim YH
• Lee SW
• Sung SK

• KMID: 2510755
• DOI: http://doi.org/10.3340/jkns.2020.0186

Abstract

Objective
: High precision and accuracy are expected in gamma knife radiosurgery treatment. Because of the requirement of clinically applying complex radiation and dose gradients together with a rapid radiation decline, a dedicated quality assurance program is required to maintain the radiation dosimetry and geometric accuracy and to reduce all associated risk factors. This study investigates the validity of Leksell Gamma plan (LGP)10.1.1 system of 5th generation Gamma Knife Perfexion as modified variable ellipsoid modeling technique (VEMT) method.
Methods
: To verify LGP10.1.1 system, we compare the treatment plan program system of the Gamma Knife Perfexion, that is, the LGP, with the calculated value of the proposed modified VEMT program. To verify a modified VEMT method, we compare the distributions of the dose of Gamma Knife Perfexion measured by Gafchromic EBT3 and EBT-XD films. For verification, the center of an 80 mm radius solid water phantom is placed in the center of all sectors positioned at 16 mm, 4 mm and 8 mm; that is, the dose distribution is similar to the method used in the x, y, and z directions by the VEMT. The dose distribution in the axial direction is compared and analyzed based on Full-Width-of-Half-Maximum (FWHM) evaluation.
Results
: The dose profile distribution was evaluated by FWHM, and it showed an average difference of 0.104 mm for the LGP value and 0.130 mm for the EBT-XD film.
Conclusion
: The modified VEMT yielded consistent results in the two processes. The use of the modified VEMT as a verification tool can enable the system to stably test and operate the Gamma Knife Perfexion treatment planning system.

Keyword

Radiosurgery; Film dosimetry; Gamma knife; Perfection

Figure

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  Fig. 1. Collimating system of GK Perfexion with 576 positions that radioisotopes can be positioned : 16 mm (), 4 mm (), 8 mm ().

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  Fig. 2. Phantom and scanner for film measurement. A : Solid-water Phantom & film. B : Epson Scanner.

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  Fig. 3. The dose distribution obtained from the data extracted from LGP and the data calculated by the VEMT method are expressed using wolfram mathematica. Comparisons of dose profiles for the 4, 8, and 16 mm collimating configurations along the x axis (A), the y axis (B), and along the z axis (C) using VEMT (-) and LGP (). LGP : Leksell Gamma plan, VEMT : variable ellipsoid modeling technique.

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  Fig. 4. Fitting does calibration curve at the red, green channel.

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  Fig. 5. Normalized intensity analysis (C) of the treatment plan (A) and the actual film survey (B) for a virtual target in the x-y plane.

Reference

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