Corewell Health William Beaumont University Hospital Royal Oak, MI
J. S. Lee, D. Mumaw, P. M. Liu, B. Loving, E. Sebastian, X. Ding, X. Cong, M. Stefani, B. Loughery, X. Li, R. L. Deraniyagala Jr, M. F. Almahariq, and T. J. Quinn; Department of Radiation Oncology, Corewell Health William Beaumont University Hospital, Royal Oak, MI
Purpose/Objective(s):The aim of this study is to explore the feasibility and dosimetric advantage of utilizing a spot-scanning proton arc approach (SPArc) for lattice radiotherapy in comparison with volumetric modulated arc therapy (VMAT) and intensity modulated proton therapy (IMPT) lattice techniques. Materials/
Methods: Lattice plans were generated for 12 large tumors across abdomen, pelvis, lung, extremity, and head-and-neck sites using VMAT, IMPT, and SPArc techniques. Lattice geometries were standardized and algorithmically generated. Vertices were 1.5 cm in diameter and arrayed in a body-centered cubic lattice with a 6 cm lattice constant. Vertices were clipped within 0.5 cm of the target border or 1.5 cm of a critical Organ-At-Risk (OAR). Prescription dose was 20 Gy(RBE) in 5 fractions to the periphery of the tumor, with a simultaneous integrated boost (SIB) of 66.7 Gy(RBE) to the vertices. OAR constraints per AAPM TG-101 were prioritized. Dose Volume Histograms (DVH) were extracted and used to identify maximum, minimum, and mean doses; equivalent uniform dose (EUD); D95%, D50%, D10%, D5%; V19Gy; peak-to-valley dose ratio (PVDR); and gradient index (GI). Treatment delivery time of IMPT and SPArc were simulated based on the published DynamicARC model. Results: Median tumor volume was 591 cc with a median of 5 high-dose vertices per plan. Low dose coverage was maintained in all plans (median V19Gy: SPArc 95%, IMPT 95%, VMAT 95%). SPArc generated significantly greater dose gradients as measured by median PVDR (SPArc 3.91, IMPT 3.62, VMAT 3.02; SPArc-IMPT p=0.0005, SPArc-VMAT p=0.002) and high-dose GI (SPArc 6.9, IMPT 10.8, VMAT 12.3; SPArc–IMPT p=0.0005, SPArc–VMAT p=0.002). There was no significant difference in simulated treatment delivery time between SPArc and IMPT (p=0.31). OAR constraints were met in all plans. Conclusion: SPArc therapy was able to achieve high-quality lattice plans for various sites with superior gradient metrics (PVDR and GI) when compared to VMAT and IMPT. Clinical implementation of RIPL is warranted.
