Do you really have OCD, or do you think you have it? OCD means you not only are anxious about certain things but that you repeat behaviors over and over because if you don't you get very anxious. I ask because so many people on here don't know what OCD really is, they think having obsessive thoughts is OCD. It isn't, everyone with a mental disorder has obsessive thoughts or they wouldn't have the disorder, and OCD is treated with different methods than other forms of anxiety. One X-ray won't give you cancer. Today's X-ray machines are much safer than the ones from years back. Now, none of them are safe, they're just safer, but despite what people hear, cancer isn't that easy to get -- you have an immune system that fights if pretty well. It takes repeated exposures to toxins for that to cause cancer. As for your back pain, if you had a lung problem, you would feel that in your back, so that explains that.
This is anxiety at work. They use a protective cover when taking x rays. You are sick only with anxiety which IS treatable. If you have OCD, what do you do about it on an ongoing basis? This is what you need to think of as the sickness, the mental health issues that make you worry about things that deep down you know are not worries. good luck