they will inform you if additional xray will be taken.they usually take one position for the chest xray, sometimes if the radiologist has a doubt on the chest xray, that is the time when they will inform you thru sms that you need to report back to medical commission, this time, they will take another xray examination. maybe 2 or 3 xray will be done then after that you have to wait for another 2-3 days, the medical result will be release. you can check every now and then thru the medical commission website so that you will know that the medical result is done.
http://www.sch.gov.qa/mcr/En/mcresults.jsp