Exhibit Hall | Forum 3
Purpose: To compare the quality of Gamma Knife (GK) vs linear accelerator (linac)-based treatment plans for stereotactic radiosurgery (SRS) of arteriovenous malformations (AVMs).
Methods: Fifteen GK SRS patients treated for AVMs between 2011-2021 were selected for this plan comparison between Eclipse and Leksell GammaPlan (LGP) treatment planning systems. The plans created on LGP were used for GK treatment, prescribed to the ~50% isodose line. The MRI and structure set (CTV and OARs) from LGP was converted to CT and DICOM transferred to Eclipse. They were used to generate linac-based SRS plans for a Varian Truebeam with a high-definition multi-leaf collimator (HD-MLC). The Volumetric Modulated Arc Therapy (VMAT) technique was applied with no heterogeneity correction, non-coplanar arcs and no PTV margins. To reproduce the coverage on LGP, a plan normalization was applied to each VMAT plan. The Paddick conformity index (PCI), mean target dose [cGy], gradient index (GI), V(20Gy) [cc], and V(12Gy) [cc] were compared.
Results: The median CTV was 0.61cc (0.07cc-5.91cc). The mean and standard deviation of PCI was 0.60±0.12 and 0.84±0.08 for GK and VMAT, respectively. The mean target dose 2718.67±657.56 and 2204.45±85.64; 3.14±0.36 and 5.60±1.44 GI; 1.50±1.88 and 1.50±1.90 V(20Gy); 1.57±1.96 and 1.56±1.99 V(12Gy). The differences were statistically significant (p<0.01) for most indexes. Irregular target volume delineation may have challenged VMAT, and the HD-MLCs may be a limiting factor at small volumes. VMAT has better beam optimization, which may explain the better PCI.
Conclusion: Higher doses of SRS may be associated with greater obliteration rates for AVMs, but also lead to an increased risk of radiotoxicity. A direct comparison of planning parameters was made in this study to determine the risk of toxicity for SRS of AVMs. Treating AVMs on GK may still be a better choice given the lower GI and higher mean target dose.