Hi tehseen:  Usually your insurance dictates how often you can have a dxa, unless you are able to pay for it yourself.  My insurance will only allow it every 24 months, and I suppose there are others that allow it more often. My insurance will pay for it more often if the Dr states that it's a medical necessity, and other insurance co's may be similar in this approach.

The National Osteoporosis Foundation also recommends it every 24 months.  If you are able to have it more often that's great, but response to osteo meds is pretty slow, so having it more often than every 2 years may not tell you much.

If your insurance will pay for it, there is another test that can be done, but this again depends on the insurance and the Dr.  Read this link that will explain this test and see if it's something your Dr will order for you.

Good luck...