Multi-Modality Beam Configuration and Uncertainty Analysis for Hybrid SBRT Treatment of Head Neck Cancer

Background: Head Neck Cancer remains one of the most technically challenging sites for radiotherapy due to the complex arrangement of critical structures surrounding the tumor volume. The adoption of hybrid Stereotactic Body Radiotherapy (SBRT), which strategically combines multiple beam modalities, has emerged as a promising approach to achieving high- dose precision while minimizing exposure to organs-at-risk (OARs). Objective: The primary objective of this study is to assess the clinical feasibility and dosimetric advantages of hybrid Stereotactic Body Radiotherapy (SBRT) using multi-modality beam configurations in metastatic head and neck cancer. Methods: Ten clinically approved treatment datasets were replanned using four distinct beam configurations. Each plan was evaluated using established dosimetric parameters, including Dose Coverage, Conformity Index (CI), Homogeneity Index (HI), and maximum OAR dose to structures such as the spinal cord, brainstem, parotid gland and canal. Additionally, plan robustness was examined through uncertainty assessment to analyze sensitivity to setup and calculation variations. Findings: The 9-beam configuration consistently demonstrated the most favorable compromise between plan quality and clinical efficiency, achieving near-ideal CI and HI values while ensuring reliable OAR protection across most cases. Lower beam counts (5 and 7) were generally inadequate in complex anatomical scenarios, resulting in inferior conformity and dose falloff. Interestingly, 11-beam plans offered superior performance only in patients with highly irregular target geometry, suggesting that beam escalation is selectively advantageous rather than universally necessary. Robustness evaluation further confirmed that hybrid beam configurations were resilient to geometric and dosimetric uncertainties, reinforcing their suitability for clinical adoption. Conclusion: Based on quantitative analysis and robustness validation, the 9-beam configuration is recommended as the optimal standard for hybrid SBRT in Head Neck Cancer, delivering an effective balance of precision, safety, and practicality. Beam escalation to 11 beams may be reserved for anatomically challenging cases where additional angular modulation enhances conformity.