Direct Comparison Between Dynamic Conformal Arcs and Volumetric Modulated Arcs in Stereotactic Radiosurgery Planning Using the High-Definition Dynamic Radiosurgery Platform for Intact Brain Metastases

Purpose This planning study aimed to directly compare the quality and efficiency of treatment planning between dynamic conformal arcs (DCA) and volumetric modulated arcs (VMA) in stereotactic radiosurgery (SRS) using the high-definition dynamic radiosurgery (HDRS) platform for unresected solitary brain metastases (BMs). Materials and methods All 20 lesions used in a previous study comparing multiple methods for optimizing DCA with the HDRS were reincluded in this study. The main constituents of the HDRS included the 5 mm leaf-width multileaf collimator (MLC) Agility^® (Elekta AB, Stockholm, Sweden) and the planning system Monaco^® (Elekta AB). Two SRS plans were created for each gross tumor volume (GTV) with DCA and VMA. In both optimizations, the dose conformity and the steepness of the dose gradient outside the GTV boundary were prioritized using the unified methods, with few exceptions, which were currently deemed optimal based on previous studies. After the optimization, each GTV coverage by the same prescription dose was rescaled according to D_{V-0.01 cc}, a minimum dose to the GTV minus 0.01 cc. The total calculation time (tCT), the reproducibility of the intended marginal dose, and the quality of dose distribution were compared. Results The tCT and the reproducibility of the GTV marginal dose were significantly shorter and higher, respectively, while the total monitor units (MU) per fraction were significantly higher in the VMA, compared with the DCA. The dose distributions of VMA were significantly superior to those of DCA in terms of the GTV dose conformity, the appropriateness of dose attenuation margin, and the steepness and concentric lamellarity of dose gradients outside and inside the GTV boundary. The dose attenuation margin was too steep for some small lesions in both the DCA and the VMA. Conclusions Compared to DCA, VMA is less efficient in irradiation; however, the quality and efficiency of treatment planning are significantly superior. VMA was positioned as the top-priority technique for SRS using the HDRS for unresected BMs. However, sufficient consideration must be given to the extremely steep dose attenuation margin and internal dose increase at the GTV boundary, depending on the case.