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Verification of Leksell GammaPlan Treatment Plans for Extend Frame Fractionated Treatments Using Gamma Knife Perfexion

M White

M White1,2*, S Yaddanapudi2, R Drzymala2, (1) University of Missouri-Columbia, Columbia, MO, (2) Washington University in St. Louis, St. Louis, MO

SU-E-T-55 Sunday 3:00:00 PM - 6:00:00 PM Room: Exhibit Hall

Purpose: To provide the GammaPlan verification tool (GPVT) for independent dose verification of the Leksell Gamma Knife Perfexion treatment planning system, Leksell GammaPlan (LGP), when planning for Extend Frame System fractionated treatments. This version allows the use of patient surface thresholding required for LGP Extend frame planning for fractionated treatments.

Methods and Materials: Matlab was used to coordinate all computations and database retrievals. The patient surface coordinates were extracted from the LGP's SQL database. This required run-length and base64 decoding and uses an affine transformation matrix to align the data with the Leksell coordinate system. Skull surface coordinates were obtained by LGP using the pixel intensity threshold between patient surface and air in CT scans. The dose calculation algorithm used was similar to that found in LGP. The dose rate per shot was found using the focal-point model, while the 3D model provided isodose lines whose shape could be compared to LGP for a given slice in a 31x31x31 dose matrix. The 3D model also provided the magnitude and location of the dose maximum.

Results: For 22 test cases, the average ratio of the dose rate from the focal-point model to LGP was 1.019±0.044. For 20 patients tested when using the 3D model, the average ratio to LGP was 1.030±0.076. Dose agreement away from the patient surface was consistently within 5%, whereas disagreement was larger at the periphery. Only one treatment plan resulted in greater than 5% difference of the LGP from both models. The isodose lines from the 3D model consistently matched the shape of the isodose lines from LGP, regardless of the discrepancy in the absolute dose values.

Conclusion: The independent dose verification tool for the Gamma Knife Perfexion was created for use with the Extend frame, and results show that it may be useful for clinical implementation.

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