One recent approach to build highly scalable and robust networked virtual environments (NVEs) is by using peer-to-peer overlay networks. Voronoi-based Overlay Network (VON) has been proposed that promises to maintain high overlay topology consistency in a bandwidth-efficient manner. VoroCast constructs a spanning tree across all AOI neighbors based on Voronoi diagrams, while FiboCast dynamically adjusts the messaging range by a Fibonacci sequence. VoroCast improves the AOI scalability of P2P-based NVEs. However, one potential drawback of the schemes is that the child node degrees are based on peers' positions, but not bandwidth capacities. Since each node in VoroCast has different bandwidth, packet loss will be unavoidable, thus neighborship consistency will become lower. VoroCast may lead to lower multicast efficiency in AOI. A self-adaptive AOI-cast based on node bandwidth usage rate is proposed in this paper to solve this problem by adjusting the child node degrees according to node bandwidth usage rate dynamically. All nodes can balance message load independently. SACast reduces delay time and ensures neighborship consistency. Compared with Voro-Cast, SACast achieves better multicast efficiency.