The mean difference in effective radiation dose ( electromagnetic tracking-control ) was -4.7 mSv ( 95 % CI , -7.01 to -2.44 mSv ; p = 0.0001 ) , and the median difference was -5.1 mSv ( 95 % CI , -7.01 to -3.56 mSv ; p < 0.0001 ) .