Effects of Institutional Experience on Plan Quality in Stereotactic Radiotherapy Using HyperArc for Brain Metastases

Background/Aim: HyperArc (HA) is an automated planning technique enabling single-isocenter brain stereotactic radiotherapy (SRT); however, dosimetric outcomes may be influenced by the planner's expertise. This study aimed to assess the impact of institutional experience on the plan quality of HA-SRT for both single and multiple brain metastases. Materials and Methods: Twenty patients who underwent HASRT for single metastasis between 2020 and 2021 comprised the earlier group, while those treated between 2022 and 2024 constituted the later group. For multiple metastases, 40 patients who received HA-SRT from 2020 2024 were divided into earlier and later treatment groups. Dosimetric parameters including gross tumor volume (GTV) doses (D98% and Dmean), volumes of the normal brain (Brain-GTV V25Gy and V30Gy), homogeneity index (HI), gradient index (GI), and total monitor unit (MU) were compared. A linear regression model was used to evaluate the effects of planning target volume (PTV) on volumes of normal brain via interaction between PTV volume and treatment era group (earlier vs. later). Results: The later group exhibited significantly higher D98% and Dmean values for both single and multiple metastases, while V25Gy and V30Gy and GI mean values were comparable. Consequently, mean HI and total MU values increased significantly. Both single and multiple metastases showed significant interaction between PTV volume and treatment era group. Conclusion: Enhanced dosimetric outcomes in the later group suggested that accumulated experience contributed to improve GTV and brain dose in HA SRT. Institutional experience is important to improve the plan quality for SRT even with automatic planning such as HA.