My personal preference for attaching anything to concrete is lead ferrells. You drill a pilot hole, tap the ferrell in flush, then use sheet metal screw into the ferrell. For a toilet especially, I use stainless steel sheetmetal screws. There are other types if screws and bolts that can be used, Tapcon is one that I have tried, but the ferrells seem to be easier for me. I use a rotary hammer/drill using a SDS bit.