I Am A 70 Year Old Male, 100 Pack Year

I am a 70 year old male, 100 pack year smoker. Baseline CT Scan in 11/14 showed 2 nodules and follow up CT in 02/15 showed a 3rd. 3 CT's later all are calcified and unchanged. Last CT of 11/16 shows another "growing" nodule (3x3mm to 5x5mm) since above of 02/14... Never reported on as it was hidden by one of above. Pulmonologist has prescribed an antibiotic for 7 days ( to isolate any mucous) and we hope for a decrease in size with another CT Scan in 3 weeks, how many CT Scans can an individual safely have within a 12 month period ?