We develop and assess radio resource management solutions for Integrated Sensing and Communications (ISAC) in 6G networks. A novel sensing topology management scheme is introduced to balance trade-offs between sensing/communication performance and resource consumption. The simulation results demonstrate the impact of the configuration of the sensing topology management scheme on the selected and the effective topology sizes, while further quantifying the sensitivity of the sensing/communication performance w.r.t. the topology size, the number of present active- and idle-mode UEs, the number of sensing tasks, the network deployment density and the radar cross section of sensing targets. This study provides valuable insights for the effective deployment and management of sensing services in 6G mobile networks.