Patients presenting with a solitary pulmonary nodule (SPN) on diagnostic imaging tests are an important group because if early stage lung cancer is treated with curative intent, five-year survival rates approach 70%. However, not all SPNs are due to lung cancer, and the accurate characterisation of SPNs is a diagnostic challenge with significant resource and cost implications.

Due to the association between nodule size and likelihood of malignancy, current management strategies are directed by nodule size. Nodules smaller than 5mm require no follow-up, while nodules larger than 8mm in diameter require further diagnostic work-up with PET/CT or biopsy. However, both approaches are expensive, and PET/CT is not uniformly available at all hospitals.

PET/CT and dynamic contrast-enhanced CT of two pulmonary nodules. The blue boxes show a malignant nodule with increased FDG avidity on PET and increased contrast enhancement. In comparison, the benign nodule in the orange boxes shows low FDG uptake and no contrast enhancement.

Dynamic contrast-enhanced computed tomography (DCE-CT) quantifies the degree of enhancement of pulmonary nodules following the administration of intravenous iodine-based contrast. The degree of enhancement reflects the extent of vascularity of the nodule, which has been shown to be an accurate marker for the diagnosis of SPNs with high sensitivity and moderate specificity. Furthermore, DCE-CT has been shown to be a more cost-effective approach in the diagnostic work-up of nodules than PET/CT. However, the studies underpinning this analysis were weak. They predominantly involved single centre studies, did not directly compare PET with DCE-CT, included pulmonary masses as well as nodules, and incorporated studies using old technology where the spatial resolution of PET/CT did not allow for accurate assessment of smaller nodules.

The SPUTNIK trial was performed to address these gaps in knowledge; comparing both the accuracy and the cost-effectiveness of DCE-CT with PET/CT in the assessment of solitary pulmonary nodules in a large multicentre trial.

Participants with a solitary pulmonary nodule (measuring 8–30mm in size) were recruited from secondary or tertiary outpatient settings at 16 hospitals within the UK. A total of 312 recruited participants underwent both PET/CT and DCE-CT and completed two years of follow-up. The final diagnosis of the nodule was based on biopsy/surgical resection, or stability over two years of follow-up imaging.

Cost-effectiveness acceptability curve for cost per correctly managed case. This shows that at low willingness-to-pay thresholds, DCE-CT is the most cost-effective strategy. At higher thresholds for willingness to pay, a combined DCE-CT and PET/CT is the most cost-effective approach.

The trial found that PET/CT is the more accurate technique for the diagnosis of solitary pulmonary nodules. However, despite the slightly poorer performance of DCE-CT, this is a more cost-effective strategy. When ‘willingness to pay’ per correctly treated malignancy was below £9,000 (€10,700), DCE-CT was always the preferable strategy. However, when society’s willingness to pay to get one more correctly treated malignancy increases to £16,000 (€19,000), the strategy that combines DCE-CT and PET/CT becomes the strategy most likely to be considered cost-effective, with a probability equal to one.

These findings have significant implications, especially in light of the introduction of CT-based lung cancer screening. The availability of PET/CT is limited to relatively few centres. The FDG radiotracer is produced off-site and supply can be unreliable, resulting in delayed or postponed examinations. In comparison, CT machines are widely available, relatively inexpensive, and a contrast examination is quick to perform. This raises the possibility of same-day progression from initial nodule detection to subsequent work-up with DCE-CT. Case selection could be achieved with AI algorithms incorporated into routine screening workstreams.

Prof. Fiona Gilbert is Head of the Department of Radiology at the University of Cambridge, Chair of the Academic Committee of the Royal College of Radiologists, and Chair of the National Cancer Research Institute Imaging Advisory Group.

Dr. Jonathan Weir-McCall is a university lecturer at the University of Cambridge and Cardiothoracic Radiologist at the Royal Papworth Hospital.

Research Presentation Session
RPS 1404a Implementing lung cancer screening

Comparative cost-effectiveness of dynamic contrast-enhanced computed tomography versus positron emission tomography in the characterisation of solitary pulmonary nodules: the SPUtNIk trial
D. Tzelis1, F. J. Gilbert2, L. Vale1, V. Benedetto3, A. Clegg3, S. Harris4, J. R. Weir-McCall2, K. Miles5, S. George4; 1Newcastle/UK, 2Cambridge/UK, 3Preston/UK, 4Southampton/UK, 5Brighton/UK

Read the full abstract in the ECR 2020 Book of Abstracts
Weir-McCall JR, et al. (2020) Comparative cost-effectiveness of dynamic contrast-enhanced computed tomography versus positron emission tomography in the characterisation of solitary pulmonary nodules: the SPUtNIk trial. Abstract RPS 1404a-4 in: ECR 2020 Book of Abstracts. Insights Imaging 11, 34 (2020). DOI 10.1186/s13244-020-00851-0