With an estimated 160,000 deaths in 2018, lung cancer is the most common cause of cancer death in the United States1. Lung cancer screening using low-dose computed tomography has been shown to reduce mortality by 20–43% and is now included in US screening guidelines1,2,3,4,5,6. Existing challenges include inter-grader variability and high false-positive and false-negative rates7,8,9,10. We propose a deep learning algorithm that uses a patient’s current and prior computed tomography volumes to predict the risk of lung cancer. Our model achieves a state-of-the-art performance (94.4% area under the curve) on 6,716 National Lung Cancer Screening Trial cases, and performs similarly on an independent clinical validation set of 1,139 cases. We conducted two reader studies. When prior computed tomography imaging was not available, our model outperformed all six radiologists with absolute reductions of 11% in false positives and 5% in false negatives. Where prior computed tomography imaging was available, the model performance was on-par with the same radiologists. This creates an opportunity to optimize the screening process via computer assistance and automation. While the vast majority of patients remain unscreened, we show the potential for deep learning models to increase the accuracy, consistency and adoption of lung cancer screening worldwide.
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This study used three datasets that are publicly available: LUNA: https://luna16.grand-challenge.org/data/; LIDC: https://wiki.cancerimagingarchive.net/display/Public/LIDC-IDRI; NLST: https://biometry.nci.nih.gov/cdas/learn/nlst/images/
The dataset from Northwestern Medicine was used under license for the current study, and is not publicly available.
The code used for training the models has a large number of dependencies on internal tooling, infrastructure and hardware, and its release is therefore not feasible. However, all experiments and implementation details are described in sufficient detail in the Methods section to allow independent replication with non-proprietary libraries. Several major components of our work are available in open source repositories: Tensorflow: https://www.tensorflow.org; Tensorflow Estimator API: https://www.tensorflow.org/guide/estimators; Tensorflow Object Detection API: https://github.com/tensorflow/models/tree/master/research/object_detection—the lung segmentation model and cancer ROI detection model were trained using this framework; Inflated Inception: https://github.com/deepmind/kinetics-i3d—the full-volume model and the second-stage model were trained using this feature extractor.
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The authors acknowledge the NCI and the Foundation for the National Institutes of Health for their critical roles in the creation of the free publicly available LIDC/IDRI/NLST Database used in this study. All participants enrolled in NLST signed an informed consent developed and approved by the screening center’s IRBs, the NCI IRB and the Westat IRB. The authors thank the NCI for access to NCI data collected by the NLST. The statements herein are solely those of the authors and do not represent or imply concurrence or endorsement by the NCI. The authors would like to thank M. Etemadi and his team at Northwestern Medicine for data collection, de-identification and research support. These team members include E. Johnson, F. Garcia-Vicente, D. Melnick, J. Heller and S. Singh. We also thank C. Christensen and his team at Northwestern Medicine IT, including M. Lombardi, C. Wilbar and R. Atanasiu. We would also like to acknowledge the work of the team working on labeling infrastructure and, specifically, J. Yoshimi, who implemented many of the features we needed for labeling of ROIs, and J. Wong for coordinating and recruiting radiologist labelers. We would also like to acknowledge the work of the team that put together the data-handling infrastructure, including G. Duggan and K. Eswaran. Lastly, we would like to acknowledge the helpful feedback on the initial drafts from Y. Liu and S. McKinney.
D.P.N. and J.J.R. are paid consultants of Google Inc. D.P.N. is on the Medical Advisory Board of VIDA Diagnostics, Inc. and Exact Sciences. M.E.’s lab received funding from Google Inc. to support the research collaboration. This study was funded by Google Inc. The remaining authors are employees of Google Inc. and own stock as part of the standard compensation package. The authors have no other competing interests to disclose.
Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
a, Diagram describing exclusions made in our analysis. b, Table describing exclusions made by the NCI when selecting images to release from NLST. Note that there were 623 screen-detected cancers but a total of 638 cancer-positive patients. The additional 15 patients were diagnosed during the screening window, but not due to a positive screening result. In this case Row 3 ‘Relevant Images’ meant that, for cancer-positive patients, there were images from the year of the cancer diagnosis, and for cancer-negative patients it meant that all 3 years of screening images were available. Note that the publicly available version of NLST downsampled the screening groups 3 (no nodule, some abnormality) and 4 (no nodule, no abnormalities). In Extended Data Figs. 2, 3, 4 and Supplementary Table 4 we present another version of the main analysis that compensates for this downsampling by upweighting patients within these groups.
Extended Data Fig. 2 Results from the reader study—lung cancer screening on a single CT volume: reweighted.
a–e, Identical to Fig. 2, except that we took into account the biased sampling done in the selection of the NLST data released. This meant that examples in screening groups 3 (no nodule, some abnormality) and 4 (no nodule, no abnormality) were upweighted by the same factor by which they were downsampled (see Extended Data Fig. 1 for further details on the groups). Model performance shown in the AUC curve and summary tables is based on case-level malignancy score. LUMAS buckets refers to operating points selected to match the predicted probability of cancer for Lung-RADS 3+, 4A+ and 4B/X. a, Performance of model (blue line) versus average radiologist for various Lung-RADS categories (crosses) using a single CT volume. The lengths of the crosses represent the confidence intervals. The area highlighted in blue is magnified in b to show the performance of each of the six radiologists at various Lung-RADS risk buckets. c, Sensitivity comparison between model and average radiologist. d, Specificity comparison between model and average radiologist. Both sensitivity and specificity analysis were conducted with n = 507 volumes from 507 patients, with P values computed using a two-sided permutation test with 10,000 random resamplings of the data. e, Hit rate localization analysis used to measure how often the model correctly localized a cancerous lesion.
Extended Data Fig. 3 Results from the reader study—lung cancer screening using current and prior CT volume: reweighted.
a–e, Identical to Fig. 3, except that we took into account the sampling done in the selection of the 15,000 patient NLST data released. This meant that for screening groups 3 (no nodule, some abnormality) and 4 (no nodule, no abnormality) we upweighted each example by the same factor by which they were downsampled. Model performance in the AUC curve and summary tables is based on case-level malignancy score. The term LUMAS buckets refers to operating points selected to represent sensitivity/specificity at the 3+, 4A+ and 4B/X thresholds. a, Performance of model (blue line) versus average radiologist at various Lung-RADS categories (crosses) using a CT volume and a prior CT volume for a patient. The length of the crosses represents the 95% confidence interval. The area highlighted in blue is magnified in b to show the performance of each of the six radiologists at various Lung-RADS categories in this reader study. c, Sensitivity comparison between model and average radiologist. d, Specificity comparison between model and average radiologist. Both sensitivity and specificity analysis were conducted with n = 308 volumes from 308 patients with P values computed using a two-sided permutation test with 10,000 random resamplings of the data. e, Hit rate localization analysis used to measure how often the model correctly localized a cancerous lesion.
a,b, Identical to Fig. 4 except that we took into account the biased sampling done in the selection of the NLST data released. This meant that for screening groups 3 (no nodule, some abnormality) and 4 (no nodule, no abnormality) we upweighted each example by the same factor by which they were downsampled. The comparison was performed on n = 6,716 cases, using a two-sided permutation test with 10,000 random resamplings of the data. a, Comparison of model performance to NLST reader performance on the full NLST test set. NLST reader performance was estimated by retrospectively applying Lung-RADS 3 criteria to the NLST reads. b, Sensitivity and specificity comparisons between the model and Lung-RADS retrospectively applied to NLST reads.
a, AUC curve for the independent data test set with n = 1,139 cases using a two-sided permutation test with 10,000 random resamplings of the data. b, For each detection that was a ‘hit’ (overlapped with a labeled malignancy), this plot shows the volume of the intersection between the detection and the ground truth divided by the volume of the union of the ground truth and the detection. In 3D, intersection over union (IOU) drops much faster than in two dimensions (2D). For example, given a 1-mm3 nodule and a correctly centered 2-mm3 bounding box, the resulting IOU will be 0.125. In 2D, a similar situation would result in an IOU of 0.25.
Extended Data Fig. 6 Examples of ROIs from the detection model and examples of cases where the model prediction differs from the consensus grade.
a, Example slices from cancer ROIs (cyan) determined by bounding boxes (red) detected by the cancer ROI detection model. The final classification model uses the larger additional context as input illustrated by the cyan ROI. b, Sample alignment of prior CT with current CT based on the detected cancer bounding box, which is performed by centering both sub-volumes at the center of their respective detected bounding boxes. When a prior detection is not available, the lung center is used for an approximate alignment. Note that features derived from this large, 90-mm3 context are compared for classification at a late stage in the model after several max-pooling layers that can discard spatial information. Therefore, a precise voxel-to-voxel alignment is not necessary. c, Example cancer-negative case with scarring that was correctly downgraded from a consensus grade of Lung-RADS 4B to LUMAS 1/2 by the model. d, Example cancer-positive case with a nodule (size graded as 7–12 mm, depending on the radiologist) correctly upgraded from grades of Lung-RADS 3 and 4A (depending on the radiologist) to LUMAS 4B/X by the model.
a, Example of model attributions for a cancer-positive case. The top row shows the input volume for the full-volume and cancer risk prediction models, respectively. The lower row shows the attribution overlay with positive (magenta) and negative (blue) region contributions to the classifications. In all cancer cases under the attributions study, the readers strongly agreed that the model focused on the nodule. Also, in 86% of these cases, the global and second-stage models focused on the same region. b, Example of model attributions for a cancer-negative case. The left-hand image shows a slice from the input subset volume. The right-hand image image shows positive (magenta) and negative (blue) attributions overlayed. The readers found that, in 40% of the negative cases examined, the model focused on vascular regions in the parenchyma.
a, 4B/X false positives. b, 4A+ false positives.
Extended Data Fig. 9 STARD diagram of low-dose-screening CT patients from an academic medical center used for the independent validation test set.
We require a minimum of 1 year of follow-up for cancer-negative cases. This resulted in a median follow-up time of 625 d across all patients once all exclusion criteria were taken into account. To clarify, this means that the median amount of time from the first screening CT to either a cancer diagnosis or the last follow-up event was 625 d. There were 209 patients (232 cases) with priors in this set of 1,139.
Extended Data Fig. 10 Illustration of the architecture of the end-to-end cancer risk prediction model.
The model is trained to encompass the entire CT volume and automatically produce a score predicting the cancer diagnosis. In all cases, the input volume is first resampled into two different fixed voxel sizes as shown. Two ROI detections are used per input volume, from which features are extracted to arrive at per-ROI prediction scores via a fully connected neural network. The prior ROI is padded to all zeros when a prior is not available.
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Ardila, D., Kiraly, A.P., Bharadwaj, S. et al. End-to-end lung cancer screening with three-dimensional deep learning on low-dose chest computed tomography. Nat Med 25, 954–961 (2019). https://doi.org/10.1038/s41591-019-0447-x
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