Program Information
CT Lung Cancer Screening and the Effects of Further Dose Reduction On CAD Performance
S Young*, P Lo , J Hoffman , H Kim , W Hsu , C Flores , G Lee , M Brown , M McNitt-Gray , UCLA School of Medicine, Los Angeles, CA
Presentations
TH-AB-207A-12 (Thursday, August 4, 2016) 7:30 AM - 9:30 AM Room: 207A
Purpose: CT lung screening is already performed at low doses. In this study, we investigated the effects of further dose reduction on a lung-nodule CAD detection algorithm.
Methods: The original raw CT data and images from 348 patients were obtained from our local database of National Lung Screening Trial (NLST) cases. 61 patients (17.5%) had at least one nodule reported on the NLST reader forms. All scans were acquired with fixed mAs (25 for standard-sized patients, 40 for large patients) on a 64-slice scanner (Sensation 64, Siemens Healthcare). All images were reconstructed with 1-mm slice thickness, B50 kernel. Based on a previously-published technique, we added noise to the raw data to simulate reduced-dose versions of each case at 50% and 25% of the original NLST dose (i.e. approximately 1.0 and 0.5 mGy CTDIvol). For each case at each dose level, a CAD detection algorithm was run and nodules greater than 4 mm in diameter were reported. These CAD results were compared to “truth”, defined as the approximate nodule centroids from the NLST forms. Sensitivities and false-positive rates (FPR) were calculated for each dose level, with a sub-analysis by nodule LungRADS category.
Results: For larger category 4 nodules, median sensitivities were 100% at all three dose levels, and mean sensitivity decreased with dose. For the more challenging category 2 and 3 nodules, the dose dependence was less obvious. Overall, mean subject-level sensitivity varied from 38.5% at 100% dose to 40.4% at 50% dose, a difference of only 1.9%. However, median FPR quadrupled from 1 per case at 100% dose to 4 per case at 25% dose.
Conclusions: Dose reduction affected nodule detectability differently depending on the LungRADS category, and FPR was very sensitive at sub-screening levels. Care should be taken to adapt CAD for the very challenging noise characteristics of screening.
Funding Support, Disclosures, and Conflict of Interest: Funding support: NIH U01 CA181156 Disclosures (McNitt-Gray): Institutional research agreement, Siemens Healthcare Past recipient, research grant support, Siemens Healthcare Consultant, Toshiba America Medical Systems Consultant, Samsung Electronics
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