Objective:To evaluate the dosimetric effects of different aperture shape controller (ASC) parameters based on the Halcyon 3.0 accelerator in the hippocampal avoidance-whole brain radiotherapy (HA-WBRT) plans.Methods:This study enrolled 13 patients treated with WBRT using a Halcyon 3.0 accelerator at the Department of Radiotherapy of the Shuguang Hospital Affiliated to Shanghai University of Traditional Chinese Medicine. According to different aperture shape controller (ASC) parameters, the HA-WBRT plans were divided into six groups, namely non, very low, low, moderate, high, and very high ASC settings, marked by AO, AVL, AL, AM, AH, and AVH, respectively. This study presented a statistical evaluation of the effects of different ASC parameters on conformity index (CI), homogeneity index (HI), radiation doses to the hippocampus and other organs at risk, and the plans’ execution efficiency. Furthermore, using two dose verification tools, namely ArcCHECK and Portal Dosimetry, this study delivered a comprehensive analysis of the differences in beam delivery precision of the plans with different ASC parameters.Results:The six groups all met the requirements for clinical treatment. They had similar CI and HI values, with no statistically significant differences ( P > 0.05). The AVH group showed better protection effects on organs at risk. Compared to the control group, the AVL group showed lower Dmax of brainstems but higher Dmax of chiasma opticum ( F = 6.26, 8.04, P < 0.05). Compared to the control group, the AH group showed lower Dmax of eyeballs but higher Dmax of optic nerves ( F = 2.04, 1.37, P < 0.05). In contrast, the AVH group exhibited lower Dmax of brainstems, eyeballs, and lens than the control group ( F = 6.26, 2.04, 2.02, P < 0.05). No statistically significant differences were observed in dosimetric indices of other organs at risk ( P > 0.05). As verified using ArcCHECK and Portal Dosimetry, the γ passing rates of the six groups were over 98% at 2%/2 mm and 100% at 3%/3 mm. The overall γ passing rates verified using ArcCHECK were lower than those verified using Portal Dosimetry. The maximum difference in the monitor unit among the six groups was less than 15, and these groups did not show significant differences in terms of execution efficiency. Conclusions:The HA-WBRT plans based on the Halcyon 3.0 accelerator can meet the requirements for clinical treatment. Different ASC parameters can significantly optimize the dosimetric parameters. Among them, the AVH parameters can highly reduce the radiation dose to organs at risk. Furthermore, different ASC parameters show insignificant effects on beam delivery precision and plan execution efficiency, meeting the verification standards for clinical therapeutic doses.