Assessing dosimetric performance of HyperArc for thyroid-associated ophthalmopathy radiotherapy

To assess the dosimetric performance of HyperArc in comparison with coplanar volumetric modulated arc therapy (c-VMAT) and non-coplanar VMAT (nc-VMAT) in the radiotherapy of thyroid-associated ophthalmopathy (TAO). This retrospective study involved 10 patients with TAO who received radiotherapy at our center from December 2021 to December 2023. A single qualified physicist generated treatment plans using c-VMAT, nc-VMAT, and HyperArc techniques on the TrueBeam machine with the Eclipse treatment planning system. We compared the dosimetric parameters for target volumes and organs at risk (OARs) among these planning approaches. Monitor units (MUs) were also evaluated to assess beam efficiency and delivery effectiveness for each plan type. Compared to c-VMAT and nc-VMAT plans, HyperArc plans achieved the highest conformity index (CI), with increases of 3.35% ( t = 3.84, P = 0.004) and 4.05% ( t = 5.01, P = 0.001), respectively. They also achieved the lowest gradient index (GI), with decreases of 29.41% ( t = -10.41, P < 0.001) and 25.11% ( t = -5.55, P < 0.001), respectively, and the lowest R 50% , with decreases of 31.69% ( t = -11.74, P < 0.001) and 28.01% ( t = -5.50, P < 0.001), respectively. In terms of the dosimetric parameters of OARs, HyperArc plans produced the best results among the three types of plans. Furthermore, HyperArc plans reduced MUs by 31.39% ( t = -8.59, P < 0.001) and 20.60% ( t = -2.70, P = 0.024) compared to c-VMAT and nc-VMAT plans, respectively. This study compared c-VMAT, nc-VMAT, and HyperArc for the radiotherapy of TAO and demonstrated the superior dosimetric performance of HyperArc. HyperArc provided better dose conformity for targets, sharper dose falloff outside targets, more effective sparing of OARs, and more efficient utilization and delivery of rays.