Comprehensive plan quality assessment of simplified volumetric-modulated arc therapy for lung stereotactic body radiotherapy

In lung stereotactic body radiation therapy, optimizing plan quality, including dosimetric quality and plan complexity, is paramount for mitigating adverse effects and enhancing dose delivery accuracy. This study evaluated the plan quality of dynamic conformal arc-based volumetric-modulated arc therapy (d-VMAT) as a simplified VMAT compared to conventional VMAT (c-VMAT) across various prescription isodose lines (PIL) and planning target volume (PTV) sizes. Twenty inoperable non-small cell lung cancer patients were retrospectively analyzed (PTV: 7.6-68.7 cm³). The prescribed dose comprised 48 Gy delivered in four fractions, encompassing 95% of the PTV, with the PIL ranging from 60 to 90% in 10% increments, using a 6X-flattening filter-free beam. The d-VMAT and c-VMAT plans were generated for each patient and PIL setting. Dose indices, including the conformity index (CI), gradient index (GI), and plan complexity, were assessed for each plan. The GI of d-VMAT closely mirrored that of c-VMAT at 60% and 70% PIL. Nevertheless, d-VMAT exhibited significantly higher GI values than c-VMAT at 80% and 90% PIL, particularly for smaller PTV sizes. Notably, d-VMAT demonstrated reduced plan complexity across all PIL compared to c-VMAT. Clinically, significant differences in CI and dose coverage between d-VMAT and c-VMAT were not observed across varying PIL settings in the range of 60-80%. The dose to the organs at risk with d-VMAT was comparable to that with c-VMAT, except at 90% PIL. In conclusion, the simplification of VMAT treatment plan using d-VMAT demonstrates superior plan quality across various PTV sizes at 60% and 70% PIL.