Patient‐specific independent 3D GammaPlan quality assurance for Gamma Knife Perfexion radiosurgery

Maria Mamalui-Hunter,Robert E Drzymala,Sasa Mutic,Sridhar Yaddanapudi,Daniel A Low,Tianyu Zhao

doi:10.1120/jacmp.v14i1.3949

Abstract

One of the most important aspects of quality assurance (QA) in radiation therapy is redundancy of patient treatment dose calculation. This work is focused on the patient‐specific time and 3D dose treatment plan verification for stereotactic radiosurgery using Leksell Gamma Knife Perfexion (LGK PFX). The virtual model of LGK PFX was developed in MATLAB, based on the physical dimensions provided by the manufacturer. The ring‐specific linear attenuation coefficients (LAC) and output factors (OFs) reported by the manufacturer were replaced by the measurement‐based collimator size‐specific OFs and a single LAC=0.0065 mm−1. Calculation depths for each LGK PFX shot were obtained by ray‐tracing technique, and the dose calculation formalism was similar to the one used by GammaPlan treatment planning software versions 8 and 9. The architecture of the QA process was based on the in‐house online database search of the LGK PFX database search for plan‐specific information. A series of QA phantom plans was examined to verify geometric and dosimetric accuracy of the software. The accuracy of the QA process was further evaluated through evaluation of a series of patient plans. The shot time/focus point dose verification for each shot took less than 1 sec/shot with full 3D isodose verification taking about 30 sec/shot on a desktop PC. GammaPlan database access time took less than 0.05 sec. The geometric accuracy (location of the point of maximum dose) of the phantom and patient plan was dependent on the resolution of the original dose matrix and was of the order of 1 dose element. Dosimetric accuracy of the independently calculated phantom and patient point (focus) doses was within 3.5% from the GammaPlan, with the mean=2.3% and SD=1.1%. The process for independent pretreatment patient‐specific Gamma Knife Perfexion time and dose verification was created and validated.PACS numbers: 87.53.Bn; 87.55.‐x; 87.56.Bg

Highlights

63 Mamalui-Hunter et al.: Patient-specific independent GammaPlan quality assurance likelihood of serious errors
Commercial solution for independent dose calculation was not available for the Gamma Knife Perfexion (LGK PFX) introduced in 2007 and its GammaPlan treatment planning software versions 8 and 9 that were installed at our institution in 2008
The dose calculation formalism was similar to the one used by GammaPlan treatment planning software[3] (Fig. 1(b)) for the geometry corresponding to the Eq [1]: dD (P) dt i dD dt calibration,16

Summary

Introduction

63 Mamalui-Hunter et al.: Patient-specific independent GammaPlan quality assurance likelihood of serious errors. The importance of independent verification of GammaKnife treatments has been described in recent publications,(1,2) which concentrated the quality assurance process of the source configuration and point dose verification. The LGK PFX has a series of significant hardware differences compared to its LGK predecessors. Relevant to this discussion is that the LGK PFX has 192 Co-60 sources, arranged in eight sectors (polar angle incremented) and five rings (increment along the patient superior–inferior (SI) axis). The more detailed information on the geometry of the new version of the Gamma Knife can be found in multiple publications.[1,2,3] As in the previous versions of Gamma Knife, highly conformal dose distributions can be generated by a combination of beam apertures, treatment times, head angle, and patient shifts relative to the system isocenter. Patient irradiation at each individual treatment position is called a “shot”

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Results

Discussion

Conclusion