Stereotactic radiotherapy for metastatic brain tumors: A comparative analysis of dose distributions among VMAT, Helical TomoTherapy, CyberKnife, Gamma Knife, and ZAP-X

This study evaluates various radiotherapy techniques for treating metastatic brain tumor (BT), focusing on non-coplanar volumetric modulated arc radiotherapy (NC-VMAT), coplanar VMAT (C-VMAT), Helical TomoTherapy (HT), CyberKnife (CK), Gamma Knife (GK), and ZAP-X. CT images and structures of 12 patients who underwent CK for a single BT were utilized. Twelve treatment plans were created for each planning device. All plans adopted the approach of prescription doses to planning target volume D99.5%. They were divided into stereotactic radiosurgery (SRS) (prescription dose; 21-23 Gy) and stereotactic radiotherapy (SRT) (prescription dose; 30-36.5 Gy) groups and the same parameters evaluated included Gradient Index (GI), Paddick Conformity Index (CI), and treatment time (t-time). In the SRS group, mean values of GI and CI values were: NC-VMAT (4.28, 0.60), C-VMAT (5.61, 0.44), HT (4.68, 0.42), CK (4.31, 0.61), GK (2.81, 0.82), and ZAP-X (2.99, 0.80). In the SRT group: NC-VMAT (3.27, 0.84), C-VMAT (3.81, 0.82), HT (3.76, 0.65), CK (2.98, 0.77), GK (2.61, 0.90), and ZAP-X (2.80, 0.84). There were no significant differences in the mean values of CI and GI between ZAP-X and GK in both groups (p > 0.05). NC-VMAT and C-VMAT had shorter t-time than other techniques in both groups. ZAP-X is relatively superior in CI and GI for small tumors, similar to GK, while differences with NC-VMAT and CK diminish as tumor volume increases. ZAP-X, CK, and GK have longer t-time than other treatment techniques, regardless of volume.