Do you mean you have a structure:
And the Polylines.Accuracy field is exactly equal to the string 'acc' for all the rows you're interested in?
And the Polylines.Accuracy field is perhaps a cell array?
IF that were the case, you could do this:
validRows = strcmp( Polylines.Accuracy, 'acc' );
And then use that as a logical index on all fields you are interested in.