Abstract
BACKGROUND AND PURPOSE: This study aimed to compare dose gradients and peripheral dose spillage across three advanced radiotherapy modalities: C-Arm Linac (TrueBeam STx), Ring Gantry (Radixact(®)), and Robotic Arm Linac (CyberKnife(®)). The focus was on evaluating their performance in delivering steep dose gradients and minimizing low-dose spillage, which is crucial for reducing toxicities and optimizing treatment outcomes. MATERIALS AND METHODS: A retrospective analysis of 110 patients with multi-lesion brain tumors treated with stereotactic radiotherapy was conducted. Patients were grouped by target volume size, and treatment plans were created using the three modalities. Dosimetric parameters, including gradient index (GI5-GI50), dose conformity, and homogeneity, were analyzed following ICRU 91 guidelines. Phantom verification using the Rando Phantom and PTW SRS1600 detector ensured clinical reliability. RESULTS: The Robotic Arm Linac demonstrated the steepest dose gradients and lowest GI values at GI10 and GI5, highlighting superior precision and minimal low-dose spillage (P < 0.05). The C-Arm Linac and ring gantry showed comparable performance at higher GI values (GI20-GI50), with the ring gantry achieving broader dose coverage for larger targets. Phantom validation supported these findings, confirming modality-specific advantages. CONCLUSION: Robotic Arm Linac is optimal for precise treatments with stringent organ-at-risk sparing, while C-Arm Linac and ring gantry are better suited for broader dose coverage in complex cases. These results provide guidance for modality selection based on tumor size and clinical needs, with potential for further optimization through artificial intelligence and advanced planning tools.