You can change the dimension prefix in radial dimensions.

1. Close Tekla Structures
2. Open the file dim_operation.ail located in ..\Tekla Structures\<version>\messages\.
3. Change the prefix R to Radius:

   string dim_operation_dim_radius_prefix{ ... entry = ("enu", "R ");};

   string dim_operation_dim_radius_prefix{ ... entry = ("enu", "Radius ");};

4. Save the changes and reopen Tekla Structures.