Population

• 7557 participants
• 46-76 years old (mean age 59)
• high risk for lung cancer
• current or former smokers
• > 15 pack years

CT protocol

Image Reading

• Read twice independently
• 1st by one of 13 radiologists 1-20 yrs experience
• 2nd by one of 2 radiologists at least 6 yrs experience

• If discrepancy
  
• 3rd radiologist > 15 yrs experience arbitrated

Volume calculation

• Syngo Lungcare software package
• 3D template generated after clicking nodule with automated volume measurements
• In 86% of >4000 nodules, double reading gave same volume
• Differences >15% found in 4% of nodules
• If volumes differed, 2nd reader measurements used

Nodule characteristics

• Indeterminate size:
• 50 - 500 mm^3 (4.6 - 9.8 mm)
• Considered benign if no growth after 2 years 
  or benign histology
• Considered resolved if disappeared on followup CT
• Peripheral defined as outer 1/3 of lung
• Margins defined as smooth vs.
  non-smooth (lobulated, irregular, spiculated)

Results: Table 1

Results: Table 2

Results: Table 3

Results: Table 4

Results: Figure 2 (smooth, round)

Results: Figure 2 (lobulated)

Discussion

Discussion

The rate and speed of disappearance higher for larger nodules (>= 8 mm)

However, rate of malignancy also higher

May be explained by benign conditions like inflammation commonly showing nodules with a larger diameter

Limitations

Precise time of nodule resolution could not be ascertained

No histology for resolving nodules

Generalizability to incidental nodules found on non-screening exams