Early and delayed FDG PET in the evaluation of lung cancer associated with pneumoconiosis

Abstract

1768

Objectives: Progressive massive fibrosis (PMF) of the lung is a type of late-stage pneumoconiosis of an aggregation of silicotic nodules fused by connective tissue. It appears rapidly and tends to increase in size. In addition, considering the high incidence of lung cancer in these patients, a diagnostic approach would be valuable that could effectively differentiate a malignant lesion from pneumoconiosis-related benign lesion. FDG PET is being increasingly applied in the evaluation of chest tumors such as lung cancer. We have assessed the value of early and delayed FDG PET in the evaluation of lung cancer associated with pneumoconiosis.

Methods: Twenty patients with pneumoconiosis entered a study to evaluate the accuracy of FDG PET in diagnosing lung cancer. FDG PET imaging (whole body) was performed at 1 hour (early) post FDG injection and repeated 2 hours (delayed) after injection only in the thoracic region. Image analysis was performed both with visual interpretation and using a semiquantitative method. The semi-quantitative analysis using the standardized uptake value (SUV) was determined for both early and delayed images (SUV1 and SUV2, respectively). The retention index was calculated with the following formula: (SUV2-SUV1) x 100/ SUV1. All semi-quantitative data were expressed as mean±SD. The results of PET imaging were compared to histological data and/or clinical follow-up.

Results: A total of 36 pulmonary mass were identified in 20 patients. Histology and/or clinical follow-up demonstrated the presence of lung cancer in 10 lesions and demonstrated PMF in the remaining 16. On visual analysis, all 36 lesions showed increased uptake on both early and delayed PET images. The uptake of FDG on delayed PET scan was significantly higher in lung cancer than in PMF (SUV2=10.1±6.1 and SUV2=5.3±2.5, respectively; p<0.04). There was no significant difference between SUV1 in lung cancer (SUV1=7.4±4.1) and PMF (SUV1=4.5±1.8). There was also no significant difference between retention index in lung cancer (31.5±14.0) and PMF (17.9±19.4). With a SUV2 cutoff of 4.5 to differentiate between lung cancer and PMF, a sensitivity was 80% and a specificity was 46%.

Conclusions: Delayed FDG PET imaging could be a useful method to detect lung cancer in patients with pneumoconiosis. But FDG PET may not always distinguish lung cancer from PMF in patients with pneumoconiosis.