Abstract
PurposeTo compare qualitative and semi-quantitative PET/CT criteria, and the impact of nodule size on the diagnosis of solitary pulmonary nodules in a prospective multicentre trial.MethodsPatients with an SPN on CT ≥ 8 and ≤ 30 mm were recruited to the SPUTNIK trial at 16 sites accredited by the UK PET Core Lab. Qualitative assessment used a five-point ordinal PET-grade compared to the mediastinal blood pool, and a combined PET/CT grade using the CT features. Semi-quantitative measures included SUVmax of the nodule, and as an uptake ratio to the mediastinal blood pool (SURBLOOD) or liver (SURLIVER). The endpoints were diagnosis of lung cancer via biopsy/histology or completion of 2-year follow-up. Impact of nodule size was analysed by comparison between nodule size tertiles.ResultsThree hundred fifty-five participants completed PET/CT and 2-year follow-up, with 59% (209/355) malignant nodules. The AUCs of the three techniques were SUVmax 0.87 (95% CI 0.83;0.91); SURBLOOD 0.87 (95% CI 0.83; 0.91, p = 0.30 versus SUVmax); and SURLIVER 0.87 (95% CI 0.83; 0.91, p = 0.09 vs. SUVmax). The AUCs for all techniques remained stable across size tertiles (p > 0.1 for difference), although the optimal diagnostic threshold varied by size. For nodules < 12 mm, an SUVmax of 1.75 or visual uptake equal to the mediastinum yielded the highest accuracy. For nodules > 16 mm, an SUVmax ≥ 3.6 or visual PET uptake greater than the mediastinum was the most accurate.ConclusionIn this multicentre trial, SUVmax was the most accurate technique for the diagnosis of solitary pulmonary nodules. Diagnostic thresholds should be altered according to nodule size.Trial registrationISRCTN - ISRCTN30784948. ClinicalTrials.gov - NCT02013063
Highlights
Solitary pulmonary nodules, defined as distinct focal pulmonary lesions ≤ 30 mm, are a relatively common finding on chest CT and present a significant opportunity to improve patient outcomes as early diagnosis of lung cancer results in excellent survival rates following surgical resection [1]
Downstream work-up of a nodule is dependent on its size with nodules < 8mms requiring CT follow-up, and nodules 8– 30 mm requiring further work-up with biopsy or PET/CT [8]. 18Fluorine fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT) has a high accuracy for the diagnosis of malignancy in nodules with a recent meta-analysis reporting a sensitivity of 89% and a specificity of 70% [5]
For a nodule to be diagnosed as malignant, histological confirmation was required or an increase in nodule size with a specialist thoracic oncology multi-disciplinary team (MDT) consensus of certainty of malignancy where biopsy/resection was not possible
Summary
Solitary pulmonary nodules, defined as distinct focal pulmonary lesions ≤ 30 mm, are a relatively common finding on chest CT and present a significant opportunity to improve patient outcomes as early diagnosis of lung cancer results in excellent survival rates following surgical resection [1]. SUV is a relative measure of FDG uptake, which is prone to variability as a result of scanner features, patient factors, imaging protocols and reconstruction algorithms [9] Due to this limitation, several authors have suggested the use of a visual ordinal scale comparing the nodule uptake to that of the mediastinal blood pool [10]. Normalising the tumour SUVmax to background tissue such as the blood pool or liver to create a standardised uptake ratio (SUR) can significantly improve the variability in quantification of tumour uptake and may overcome some of the inherent limitations of isolated tumoral SUVmax measurement [11] This in turn may allow for a more nuanced approach to nodule assessment and follow-up through the use of a semi-quantitative metric rather than allowed for within the visual ordinal system
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