CyberKnife and EDGE in stereotactic body radiotherapy for pancreas cancer: a comparison of plan quality

Abstract

Purpose: To perform a comprehensive comparison of the different stereotactic body radiotherapy (SBRT) plans between the Varian EDGE and CyberKnife (CK) systems for pancreas cancer.Materials and methods: Fifteen patients with pancreas cancer were selected in this study. The median planning target volume (PTV) was 28.688cm 3 (5.736 to 49.246 cm 3 ). The SBRT plans for the EDGE and CK were generated in the Eclipse and Multiplan systems respectively with the same contouring and dose constrains for PTV and organ at risk (OAR). Dose distributions in PTV were evaluated in terms of coverage, conformity index (CI), new conformity index (nCI), homogeneity index (HI), and gradient index (GI). OARs, including spinal cord, bowel, stomach, duodenum and kidneys were statistically evaluated by different dose-volume metrics and equivalent uniform dose (EUD) . The volume covered by the different isodose lines (ISDL) ranging from 10% to 100% for normal tissue were also analyzed.Results: All SBRT plans for EDGE and CK met the clinical requirement for PTV and OARs. . For the PTV, the dosimetric metrics in EDGE plans were lower than that in CK, except that D 99 and GI were slightly higher. The EDGE plans with lower CI , nCI and HI were superior to offer the better conformity and homogeneity for PTV. For the normal tissue, the CK plans were better at OARs sparing. The radiobiological indices EUD of spinal cord, duodenum, stomach, and kidneys were lower for CK plans, except that liver were higher. The volumes of normal tissue covered by medium ISDLs (with range of 20%~70%) were lower for CK plans while that covered by high and low ISDLs were lower for EDGE plans.Conclusions: This study indicated that both EDGE and CK generated equivalent plan quality, and both systems can be considered as beneficial techniques for SBRT of pancreas cancer. EDGE plans offered the better conformity and homogeneity of dose distributions for PTV, while the CK plans could minimize the exposure of OARs.