You can do it, but you need to understand that it's not as obviously good an idea as you might think. Here is an article that explains why:
http://www.slate.com/articles/news_and_politics/explainer/2010/11/fullbody_scam.html
But if you don't want to read this, then the main points are: be prepared for THE 20-90% chance that they will find an ordinary cyst or piece of scar tissue that they will need to investigate. Realize that a CT scan does not do well with abdominal cancer unless they specifically use contrast dye, which they won't in this situation, and the people who would profit from this, the radiologists, are against preventive full body scans.