Dosimetric Impact of Automated Non-Coplanar Treatment Planning Using Stereotactic Radiosurgery for Multiple Cranial Metastases: Comparison between Hyperarc and Cyberknife Dose Distributions

Abstract

The purpose of this study was to clarify the dosimetric impact of automated non-coplanar treatment planning, HyperArc-based stereotactic radiosurgery (SRS) for multiple cranial metastases by comparing with Robotic Radiosurgery System, Cyberknife planning. Eleven cancer patients with multiple cranial metastases (range of the number of tumors: 3 to 5) treated by CyberKnife M6 (Accuray Inc, Sunnyvale, USA) in the period from January 2016 to December 2017 were selected for this study. MultiPlan (Accuray Inc, Sunnyvale, USA) with Ray-tracking dose calculation algorithm was used as a radiation treatment planning system. The GTV was defined as the area of contrast enhancement on MRI and PTV was equal to GTV. The treatment dose of 23 Gy per single fraction was prescribed to the 70%-80% isodose line covering 95% of PTV. The dose to the surrounding healthy brain and organs at risk (e.g., brain stem) were optimized to minimize complications for all plans generated using our institutional protocol; PTV Dmin > 20 Gy, brainstem Dmax < 15 Gy, spinal cord Dmax < 14 Gy, optic nerve Dmax < 10 Gy, and optic chiasm Dmax < 10 Gy. These plans were replanned with an automated non-coplanar treatment planning solution implemented in a treatment planning system, named HyperArc. HyperArc plan were designed using four non-coplanar arc single-isocenter VMAT in 6MV flattening filter free mode for simulated delivery with the True beam STx (Varian) in high intensity with HD-MLC. One isocenter was used for all targets and was placed at the center of mass of all targets. Dose calculation algorithm was Acuros XB. Dosimetric differences were evaluated using target conformity/homogeneity (Paddick CI and HI), dose fall-off (gradient index) and radiation necrosis indicator (total brain V12-GTV). Summary of DVH paramters for two plans are shown in table 1. PTV CI, HI and GI were 0.60±0.11, 1.72±0.22, and 3.94±0.74, respectively, for Cyberknife plan, whereas they were 0.87±0.08, 1.44±0.05, and 5.31±1.42, respectively, for HyperArc plan (p <0.05). Total brain V12-GTV for Cyberknife and HyperArc were 5.26±2.83 cm3 and 4.02±1.71, respectively. These results showed that HyperArc plan had better CI, HI and total lung V12-GTV, although Cyberknife had better GI.Abstract TU_31_3204; Table 1DVH parameterHyperArcCyberknifePTV maximum29.78±0.9233.60±2.61 minimum20.73±0.2719.71±1.34 mean25.88±0.2727.53±1.01 HI1.44±0.051.72±0.22 CI0.87±0.080.60±0.11 GI5.31±1.423.94±0.74Total brain mean1.15±0.290.97±0.35 V12-GTV4.02±1.715.26±2.83 V2163.00±78.84151.20±89.73 Open table in a new tab We compared HyperArc and Cyberknife plans for brain multiple metastases SRS for the first time. Our results demonstrated that HyperArc-based SRS planning had the great potential for being suitable tool for brain multiple metastases SRS.