Pulmonary nodule growth: can follow-up be shortened with a high-end or an ultra-high-resolution CT scanner?

PURPOSE: To determine the interscan variability of pulmonary nodule volume measurements in CT scans acquired with state-of-the-art wide-area and ultra-high-resolution CT systems. METHODS AND MATERIALS: In this prospective study, patients with at least two non-calcified solid pulmonary nodules suspicious for metastases on previous CT scans were imaged twice with either a high-end 320 detector CT (MDCT, Aquilion ONE Genesis, Canon, slice thickness 0.5 mm, 512x512 matrix) or an ultra-high-resolution CT (UHRCT, Precision, Canon, 0.25 mm, 1024x1024). In between scans, an off-and-on table strategy was used to simulate follow-up scans with no nodule growth. Semi-automated volumetric nodule segmentation and volume estimation (max. 4 per patient, effective diameter 4-15 mm) were performed on a lung screening workstation (Veolity). 95%-limits of agreement (LOA) and the time to estimate actual nodule growth rate at a nodule volume doubling time (VDT) of 400 days were calculated. RESULTS: 17 patients (60 nodules, average volume: 218 mm3) were imaged on the MDCT and 27 patients (90 nodules, 177 mm3) on the UHRCT at a similar dose (mean dose-length-product: 126.6 mGycm vs 127.2 mGycm, respectively (p=0.98)). The 95%-LOA was +-7.0% for the MDCT and +-5.9% for the UHRCT (p=0.07). Therefore, the minimum required interscan period to detect a VDT of 400 days is 33-39 days. CONCLUSION: Both scanners result in low interscan variability, especially compared to current clinical standards, which requires a volume change of 25% (the current 95%-LOA) as significant nodule growth. Therefore, the follow-up period to detect pulmonary nodule growth could be dramatically shortened from three to about one month, reducing patient anxiety and the potential for stage shift in lung nodule management. LIMITATIONS: Pulmonary metastases instead of incidental nodules were measured.