Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: Radius
FIELD_TORUS_RADIUSParameter: Thickness
FIELD_TORUS_THICKNESSParameter: Direction
FIELD_TORUS_DIRECTIONParameter: Clip to Shape
FIELD_TORUS_CLIP