Can I substitute chest x-ray with a chest ultrasound?

I had some consolidation in my chest in 1999 which got resolved in 15 days. But to check and verify the condition i had around 10 x-rays done in three months. Subsequently up till now (2008), every time i cough, various docs have put me through numerous (totaling 22!!!) x-rays. Now these x-rays really scare me..... Can i suggest the doc an ultrasound of the chest instead???