Lung nodule detection with ultra-low-dose CT in routine follow-up of cancer patients

Purpose: To evaluate the value of an ultra-low-dose CT protocol (ULD-CT) in the dectection of lungnodules in follow-up of cancer patients. Material and Methods: Between April and August 2003, 72 consecutive patients with a history of malignancy were prospectively examined on a single-slice helical CT scanner (Aquilion, Toshiba) with ULD-CT (120 kV, 5 mAs, D-eff 0.12 mSv) and regular-dose CT (R-CT) (120 kV, 150 mAs, D-eff 4.8 mSv). The ULD-CT examinations were independently evaluated by two radiologists. Afterwards, consensus reading of the ULD-CT and R-CT examinations was done. Individual nodules were classified benign (benign calcifications) and non-benign. The studies were classified in 4 subgroups: 1) non-benign nodule evident; 2) non-benign nodule probable; 3) non-benign nodule possible, but not, likely; 4) no-non benign nodule. Results: ULD-CT detected 180 nodules in 47 patients, while R-CT showed 168 nodules in 39 patients. The sensitivity of ULD-CT was 87% in detecting nodules regardless of size and 94 % in detecting nodules >= 5 mm. Regarding the prediction of a case with non-benign nodules (subgroups 1 to 3), the sensitivity of ULD-CT was 94% and the specificity 75 %. Conclusion: ULD-CT is a good diagnostic tool in detecting lung nodules >= 5 mm. Radiation dose can be markedly reduced. A negative ULD-CT study excludes non-benign nodules in R-CT with a high probability. In case of a positive ULD-CT, R-CT can be immediately followed.