Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: Radius
FIELD_TORUS_RADIUS
Parameter: Thickness
FIELD_TORUS_THICKNESS
Parameter: Direction
FIELD_TORUS_DIRECTION
Parameter: Clip to Shape
FIELD_TORUS_CLIP