Difference in Radiotherapeutic Plan of HyperArc-Based and CyberKnife-Based Stereotactic Radiotherapy (SRT) Techniques for Multiple Brain Metastases

Abstract

The purpose of this study is to compare the dosimetric quality and dose to surrounding normal tissue of HyperArc-based stereotactic radiotherapy (SRT) technique with a frameless robotic radiosurgery system for patients with multiple brain metastases. Nineteen patients with multiple brain metastases (2-5 lesions) treated in our center were enrolled. The prescribed dose was 2100 cGy to 3250 cGy in three to five fractions. In order to determine the dosimetric quality, we compared the conformity index (CI), Gradient radius (GR), homogeneity index (HI), dose distribution in planning target volume, and dose to several organs at risk (OARs). All of the data were compared using pair-T test. Both planning systems have prescribed dose coverage to GTV and PTV with no significant difference (P = 0.243; P = 0.312). The conformity index (CI), and homogeneity index (HI) were 1.27 ±0.022, and 1.08 ±0.006, respectively, for HyperArc plan and 1.76 ±0.065 and 1.22 ±0.009, respectively, for the CK plan (both, P< 0.001). The Gradient radius (GR) was 0.732 ±0.056 cm for HyperArc plan and 0.847 ±0.762 cm for CK plan (P = 0.002). These indicated that HyperArc plan had better CI, HI, and GR when compared to CK plan. Maximum dose to brainstem for HyperArc and CK plans were 485.1 ±128.65 and 723.6 ±126.93 cGy, respectively (P < 0.001). Moreover, HyperArc plan had less mean dose to optic chiasm, bilateral eyes, bilateral lens, and bilateral optic nerves (all, P < 0.05). Brain V5, V12, V24 were all much smaller in HyperArc plan (all, P < 0.05), indicating that HyperArc plan delivered less dose to normal brain tissue. For patients with two to five brain metastases, HyperArc-based SRT provide excellent dosimetric quality and less dose to normal tissue.