After passing medical commission (via mansoura round about), you will cross woqod petrol station, take right immediately in the roundabout. Then you will reach again a round about. Take left(3rd exit) then you have to drive long, until you reach a round about. Take "U" turn and almost drive the same way back. After crossing qatar scientific club, you can see a right exit (similar exits are there, take care). When you take right exit, go in and follow the left curve of the road and you will reach QDC... Enjoy