Dosimetric Comparison between CyberKnife and GammaKnife Hypofractionated Radiosurgery for Benign Perioptic Tumors: A Retrospective Multi-institutional Study

Abstract

Objective: We conducted a retrospective multi-institutional study to compare the dosimetric differences between the CyberKnife (CK) and the Gamma Knife (GK) in treatment planning of hypofractionated stereotactic radiosurgery (hSRS) for benign perioptic tumors.

Methods: We selected 16 perioptic tumors previously treated using CK between 2011 and 2015. In each case, two separate GK plans (GK1 and GK2) at two different institutions were retrospectively generated using the identical planning CT images and contour set of the original CK plan. Thus, a triplet data set of dosimetric parameters for each lesion was generated and compared. The planning objective was maximizing dose to tumor, while satisfying the proposed dose-volume constraints criteria (Dmax < 25 Gy and V20Gy < 0.2 cc) for the optic apparatus (OA).

Results: All treatment plans achieved a high level of conformity index (1.22 for CK, 1.21 for GK1, and 1.20 for GK2 plan, respectively; P=0.025), while doses to OA were well within the intended dose-volume limits. However, statistically significant differences in other dosimetric parameters were observed: D99%, 25.6 Gy for CK vs. 24.9 Gy and 23.9 Gy for GK1 and GK2, respectively (p < 0.001); tumor coverage, 95.1% for CK vs. 90.5% and 95.1% for GK1 and GK2, respectively (p = 0.002); and gradient index, 3.10 for CK vs. 2.85 and 2.61 for GK1 and GK2, respectively (p < 0.001).

Conclusions: Both CK and GK systems appear to provide a comparably high quality dosimetric planning for perioptic tumors, although slight differences in dosimetric parameters between these modalities exist.