Room: AAPM ePoster Library
Purpose: HybridArc combines dynamic conformal arcs with static field intensity-modulated radiotherapy (IMRT) beams. HybridArc has demonstrated superior dose conformity in cranial plans. Volumetric modulated arc therapy (VMAT) represents the current advanced external beam treatment method. We compare their dosimetric performance for intracranial fractionated stereotactic radiotherapy (FSRT).
Methods: Seven FSRT brain patients were planned using Brainlab iPlan RT Dose (v4.5) for HybridArc and Varian Eclipse (v15.6 with the Photon Optimization algorithm) for VMAT. HybridArc plans used 5-6 IMRT beams with 20-30% weighting over the 3-4 noncoplanar dynamic conformal arcs. The VMAT plans were created using the same arc geometry as the HybridArc plans. All plans were prescribed to 54 Gy in either 1.8 or 2 Gy fractions and normalized so that 100% of the prescription dose covered 95% of the planning target volume (PTV). PTV sizes were 3.3 to 28.6 cc. The conformity index (CI), gradient index (GI), homogeneity index (HI), brainstem and chiasm max dose, and monitor unit (MU) efficiency were used to evaluate plan quality.
Results: On average, compared to the VMAT plans, HybridArc plans were more conformal (1.7% lower CI), had less intermediate dose spillage (8.6% lower GI), had lower hotspots (1.2% lower HI), and were more efficient in modulation (8.0% lower MU). Brainstem and chiasm max dose was similar between the two plans.
Conclusion: Despite using the newest advanced Photon Optimization algorithm for VMAT plans, the HybridArc combination of dynamic conformal arcs and IMRT beams produced more conformal plans with more homogeneous coverage while maintaining similar OAR sparing.