At 7 years , the LF rate was 0.9 % ( 95 % CI , 0.0 % to 2.2 % ) in the RT arm versus 6.7 % ( 95 % CI , 3.2 % to 9.6 % ) in the observation arm ( hazard ratio , 0.11 ; 95 % CI , 0.03 to 0.47 ; P < .001 ) .