At the region file help page of ds9 we read that we can define position arguments in a region file by placing the numbers along with the right character, e.g. 17.845d for degrees, 16.234p for pixels.
Even though that radians are stated to be working (by placing the r character, like 12.123r), that finally DOES NOT WORK !!
I cannot understand why this happens (I even mailed them but without any answer yet!) and the only option is to convert radians to degrees before actually use them.