Dosimetric comparisons among different treatment planning systems for spinal SBRT for doughnut-shaped bone metastases
Keywords:
CyberKnife, Dose gradient, SBRT, VMATAbstract
Backgrounds: Stereotactic Body Radiotherapy (SBRT) for doughnut-shaped spinal metastases presents challenges due to their irregular shapes. Various treatment planning systems (TPSs) can deliver these plans through either volumetric modulated arc therapy (VMAT) on linear accelerator machines or robotic radiosurgery, such as CyberKnife®. However, no direct comparison among Eclipse™, Elements®, and Precision® exists to evaluate dosimetric outcomes.
Objectives: This study aims to compare the dosimetric outcomes among VMAT plans utilizing Eclipse® and Elements® versus CyberKnife® plans using Precision®. The focus is on the dose gradient from the planning target volume (PTV) to the spinal cord surface, referred to as the parameter Vinter.
Materials and Methods: Five doughnut-shaped lesions were re-contoured and re-planned. VMAT plans using Eclipse™ and Elements® were performed with identical parameters. CyberKnife® plans using Precision® were generated with parameters similar to those of VMAT plans. The prescription dose was 30 Gy in 5 fractions to the PTV. Primary considerations were ensuring that at least 95% of the PTV received the prescription dose while maintaining spinal cord constraints. Dosimetric comparisons included the dose gradient from the PTV to the surface of the spinal cord (Vinter), plan evaluation metrics, doses to the spinal cord, monitor units (MUs), and beam-on time.
Results: All treatment plans met the PTV criteria while maintaining spinal cord constraints, except for two plans with Precision®. Vinter was steeper with Eclipse™ compared to Elements® and Precision® (Vinter = 1.33, 1.38, and 1.78, respectively). Eclipse™ achieved superior dose conformity (inverse paddick conformity index = 1.07, 1.15, and 1.24, respectively) and more homogeneous doses than Elements® and Precision® (Homogeneity index = 0.15, 0.26, and 0.32, respectively). Elements® demonstrated a steeper dose fall-off, resulting in a lower gradient index compared to Precision® and Eclipse™ (Gradient index = 2.73, 2.99, and 2.99, respectively) and delivered lower doses to the spinal cord than Eclipse™ and Precision® (D0.35cc = 20.06 Gy, 21.62 Gy, and 21.59 Gy, respectively). Elements® also indicated lower MUs and beam-on time. Elements® also indicated significantly lower fractions of MUs and beam-on time than Precision®.
Conclusion: Both Eclipse™ and Elements® demonstrated comparable overall dosimetric outcomes for doughnut-shaped lesions and potentially superior treatment efficacy compared to Precision®.
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