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. 2016 Jul 8;17(4):190-201.
doi: 10.1120/jacmp.v17i4.6196.

Development of a Monte Carlo model for treatment planning dose verification of the Leksell Gamma Knife Perfexion radiosurgery system

Jiankui Yuan  1 , Simon S Lo, Yiran Zheng, Jason W Sohn, Andrew E Sloan, Rodney Ellis, Mitchell Machtay, Barry Wessels
Affiliations

Development of a Monte Carlo model for treatment planning dose verification of the Leksell Gamma Knife Perfexion radiosurgery system

Jiankui Yuan et al. J Appl Clin Med Phys. .

Abstract

Detailed Monte Carlo (MC) modeling of the Leksell Gamma Knife (GK) Perfexion (PFX) collimator system is the only accurate ab initio approach appearing in the literature. As a different approach, in this work, we present a MC model based on film measurement. By adjusting the model parameters and fine-tuning the derived fluence map for each individual source to match the manufacturer's ring output factors, we created a reasonable virtual source model for MC simulations to verify treatment planning dose for the GK PFX radiosurgery system. The MC simulation model was commissioned by simple single shots. Dose profiles and both ring and collimator output factors were compared with the treatment planning system (TPS). Good agreement was achieved for dose profiles especially for the region of plateau (< 2%), while larger difference (< 5%) came from the penumbra region. The maximum difference of the calculated output factor was within 0.7%. The model was further validated by a clinical test case. Good agreement was obtained. The DVHs for brainstem and the skull were almost identical and, for the target, the volume covered by the prescription (12.5 Gy to 50% isodose line) was 95.6% from MC calculation versus 100% from the TPS.

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Figures

Figure 1
Figure 1
A cylindrical phantom (a) installed in the Leksell Gamma Knife frame for irradiation; 5 mm bolus on the top of the EBT film is not shown in the figure. Source images (b) of 16 mm collimator for one sector on the film.
Figure 2
Figure 2
Relative dose profiles of 4, 8, and 16 mm collimators compared with PFX TPS along x‐axis (a) and z‐axis (b).
Figure 3
Figure 3
Dose profiles along x‐axis (a) and z‐axis (b) compared with PFX TPS for the clinical test case.
Figure 4
Figure 4
Illustration of MC calculated isodose lines overlay with PFX TPS for three planes: (a) axial, (b) sagittal, (c) cornal. MC: thick lines; TPS: thin lines. Blue: 3 Gy; red: 12.5 Gy; yellow: 15 Gy; green: 20 Gy.
Figure 5
Figure 5
MC‐calculated DVHs for the target and organ at risk compared with PFX TPS for the clinical test case.
See this image and copyright information in PMC

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