A ct scan says - emphysematous bullae, should be monitored regularly, and ct scan repeated if "medically warranted." what this means and what to do?

Emphysematous: bullae are changes of emphysema. 'Monitored regularly' is a vague recommendation, but the radiologist is suggesting serial follow up at unspecified intervals. The radiologist likely does not know the full clinical picture, so 'medically warranted' means that the decision for follow up should be based on your doctor's evaluation of your entire clinical situation, not just xray pictures.