Here is what Cleveland Clinic has to say about lung nodules - it appears half of all adults have them, and I am willing to guess that the older we get, the more likely we are to have them.
https://my.clevelandclinic.org/health/diseases/14799-pulmonary-nodules
Mine are the result of many infections and a lung condition called Bronchiectasis. When the infection was active, the scans were repeated every 6 months. Now, it is every 2-3 years - as much to see if the bronchiectasis is progressing or the infection has returned as to look for changes in the nodules.