Document Type

Conference Proceeding

Publication Date


Publication Title

Medical Physics


Purpose: To develop spot-scanning proton (SPArc) and heavy ion (SHArc) arc therapy for single-isocenter stereotatic radiosurgery (SISRS) of multiple brain metastases (MBMs). First results achieved with dedicated planning infrastructure are compared to state-of-the -art volumetric modulated photon arc therapy (HA-VMAT). Methods: A multi-institutional collaboration was established to develop bespoke SPArc and SHArc SISRS infrastructure with available research and commercial treatment planning systems. Devised planning and delivery methods considered dedicated energy, spot, and multi-arc selection strategies. SPArc and SHArc (carbon and helium ions) plans were generated for MBM patients exhibiting 3-12 intracranial lesions with GTV volumes between 0.03ccm and 19.8ccm, at prescribed doses between 15Gy and 18Gy. PTVs considered a 1mm isotropic margin around the GTV, and robust optimization with 2.5%/1mm criteria for range and position was applied. Different clinical and emerging RBE models were employed. HA-VMAT plans were generated with the HyperArc platform (Varian Medical System) for the PTVs. Results: SPArc and SHArc plans were comparable, achieving highly conformal target doses and satisfying clinical coverage criteria. Particle arc plans reduced V2Gy in the healthy brain compared to HA-VMAT, at similar or increased intermediate doses depending on the number of lesions. Recent RBE models (LEMIV) predict further improved SHArc(12C) performance compared to clinical estimates (LEMI). SHArc(12C) reached a high linear energy transfer focus inside the target relevant to overcoming hypoxia (>100keV/μm). Conclusion: We present the first particle arc strategies for MBM SISRS. Achieving target dose conformality comparable to state-of-the -art HA-VMAT at improved low dose bath and increased mean target LET, SPArc and SHArc are promising candidates for MBM treatments. Differences in RBE models influence the comparison between modalities, especially for the high fraction doses applied. Further optimization of the treatment planning procedures is ongoing, focusing on improving the intermediate dose to the brain and increase delivery efficiency in cases with many lesions





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American Association of Physicists in Medicine 65th Annual Meeting & Exhibition, July 23-27, Houston, TX