2274 - Dosimetric Comparison of a Novel Automated Noncoplanar Volumetric-Modulated Arc Therapy Technique and a Robotic Radiosurgery System in Stereotactic Radiosurgery of Vestibular Schwannomas
Presenter(s)
Z. Xiong1,2, L. Zhou2, K. Xu1, L. Bell2, F. Warburton2, D. Huang2, S. B. Motwani1,2, C. S. Cathcart2, K. Nie1, N. J. Yue1, and Y. Zhang1; 1Rutgers Cancer Institute of New Jersey, New Brunswick, NJ, 2RWJBarnabas Health, Livingston, NJ
Purpose/Objective(s): To compare dosimetric outcomes for the target and organs at risk (OARs) in patients with vestibular schwannoma (VS) treated using a novel automated noncoplanar volumetric-modulated arc therapy (NC-VMAT) technique on a standard linear accelerator (Linac) versus a robotic radiosurgery system (RRS).
Materials/Methods: Fifteen patients with VS previously treated using stereotactic radiosurgery (SRS) on an RRS at our institution were retrospectively replanned with an automated NC-VMAT technique. Each plan used four noncoplanar, preconfigured partial arcs on a standard Linac but employed different multileaf collimators (MLCs): (1) a standard MLC (SMLC; 5.0 mm leaf width), and (2) a high-definition MLC (HDMLC; 2.5 mm leaf width). All plans were prescribed 12.5 Gy in one fraction to the planning target volume (PTV), while minimizing dose to OARs. The planning process used a single optimization cycle with preset templates and minor parameter adjustments as needed. All NC-VMAT plans were normalized to match the corresponding RRS plan coverage for each patient. Dosimetric comparisons included target coverage, the Paddick Conformity Index (PCI), the ICRU-83 homogeneity index (HI), the Gradient Index (GI), and doses to OARs. One-way analysis of variance (ANOVA) with a threshold of p < 0.05 was used to assess statistical significance.
Results: Compared with RRS, both NC-VMAT plans (SMLC and HDMLC) showed significantly higher D98% for the PTV (12.35 ± 0.52 Gy [RRS] vs 12.54 ± 0.28 Gy [SMLC] vs 12.57 ± 0.35 Gy [HDMLC], p < 0.005) and significantly lower Dmax (15.25 ± 0.32 Gy [RRS] vs 14.70 ± 0.39 Gy [SMLC] vs 14.73 ± 0.32 Gy [HDMLC], p < 0.002), reflecting superior target coverage and reduced hotspots. In addition, HI was significantly better for NC-VMAT (0.19 [RRS] vs 0.15 [SMLC] vs 0.14 [HDMLC], p = 0.001), and the GI was significantly lower (5.97 ± 1.24 [RRS] vs 4.79 ± 1.45 [SMLC] vs 4.37 ± 1.23 [HDMLC], p < 0.001), indicating more homogeneous dose distributions and faster dose fall-off with NC-VMAT. However, PCI was higher with RRS (0.83) compared with SMLC (0.74, p = 0.005) and HDMLC (0.77, p = 0.026), although HDMLC surpassed SMLC in PCI (p < 0.001). No significant differences were observed among techniques regarding PTV Dmean, PTV Dmin, or the maximum dose to OARs.
Conclusion: Automated NC-VMAT, particularly with HDMLC, demonstrates dosimetric performance comparable to RRS for SRS of VS. NC-VMAT plans achieved improved target coverage, fewer hotspots within the PTV, and superior HI and GI, although RRS plans provided a higher PCI. These findings support the potential of automated NC-VMAT as a preferred technique for treating VS in the context of treatment planning.