Dosimetric Evaluation between Varian’s Eclipse SRS Hyper-Arc and Elekta’s Leksell Gamma-Plan
Abstract
Purpose
To evaluate stereotactic radiosurgery (SRS) plans for Varian’s Eclipse HyperArc on TrueBeam Edge and Elekta’s Leksell GammaPlan (LGP) on Perfexion.
Methods
Cubic phantom containing five 1cm diameter spheres was imaged using Philips Big Bore CT Simulator while contouring five spheres as tumors and OAR structure for the brainstem. CT/structures were sent to LGP and Eclipse for planning using equivalent prescriptions. LGP’s dose optimization balanced low dose and beam-on time to achieve conformity index (CI) = 1.0, Paddick CI (PCI) = 1.0, and gradient index (GI) < 3.0. Similarly, Eclipse incorporated SRS HyperArc technique for automatic isocenter calculation, although collimator angles were manually entered to position targets within Edge’s HD MLCs; optimization utilized the SRS normal tissue objective (NTO) to promote steep dose gradients with higher prescription target coverage. Target quality metrics and DVH indices were compared.
Results
LGP and HyperArc’s V90% and V95% are identical for all targets, while V100% has maximum difference of 0.3%. LGP’s V105%, D98%, D95%, D50%, and mean dose exceed HyperArc’s with averages of 2.1%, 15cGy, 33cGy, 113cGy, and 82cGy, respectively, indicating increased target dose escalation for LGP. Notably, PCI maximum difference was only 0.04, but LGP’s CI and GI were closer to 1.0 and 3.0, respectively; CI and GI had lower averages of 0.09 and 0.73, respectively, demonstrating LGP’s dose conformality and sharp dose gradients. Furthermore, LGP also demonstrates greater conformality at low doses as evidenced by smaller average distance to 50% isodose (2.7mm for LGP versus 3.5mm for HyperArc); however, HyperArc minimizes dose bridging between adjacent targets with this effect occurring at 500cGy compared to 700cGy for LGP.
Conclusion
Although LGP offers higher target doses with superior dose fall-off, SRS HyperArc provides comparable plan quality with nearly equivalent PCI while improving patient comfort with reduced treatment times (~6min versus ~115min) and frameless immobilization.