The built-in PBG component will not support a circular lattice but you could design an build the PCF using the VBSCript functionality. As with your previous PCF question the limitation will be computational resources based on the overall domain size and resolution you will require for this structure.
If you go to the help menu in the menus you will find the VBScript manual which has all of the function commands accessible to you. Additionally we have a webinar that looked at some of the VBScript functionality. Under the support drop down on this site you will see an option to watch webinars. I would suggest “OptiFDTD: Advanced Features” as it looks at some uses of the VBScripting capabilities.