Can Tc-99m tetrofosmin/sestamibi lung scintigraphy differentiate malignant from benign lung masses?

Full text: Lung cancer is a leading cause of death in many countries. Surgery remains the mainstay of treatment if diagnosed in early stages. However, the differentiation of malignant from benign lung lesions poses a major diagnostic problem in this part of world since tuberculosis is a very common lung ailment in most of the developing countries. The present study was planned to evaluate the usefulness of Tc99m-tetrofosmin/sestamibi lung scintigraphy to differentiate malignant from benign lung lesions. A total of 52 patients (37 male and 15 female), age ranging from 22-75 years (mean age 56.5 ± 11.2 years) with lesions on x-rays and/or CT were recruited for this prospective study. The anterior static images were acquired at 30 minutes after intravenous injection of 555 MBq of Tc99m-tetrofosmin/sestamibi. The images were acquired by a large field of view gamma camera, fitted with low energy parallel hole collimators. The anterior static images of 500 K counts in 256 x 256 matrix were obtained at 30, 60 and 120 minutes after intravenous injection. In this study the 30 minutes data was used for calculating T/N ratio. Sixty and 120 minutes data was used for the calculation of wash out ratio to validate the multi-drug resistance hypothesis (not reported in this abstract). Region of interest were marked on the lesion (T) and normal lung (N) for semi-quantitative analysis. Final diagnosis was made on histopathological biopsy/ aspiration cytology and or cytology/culture from bronchoalveolar lavage. Of the 52 patients, 30 patients had carcinoma of lungs and 22 had pulmonary infections (non-malignant). Among the 30 patients with carcinoma, 14 had squamous cell carcinoma, 11 had adenocarcinoma, 4 had small cell carcinoma and 1 had anaplastic carcinoma. In the 22 patients with non-malignant lesions, 20 had pulmonary tuberculosis, one had radiologically atypical pneumonia and one had bronchiectasis. All lesions were picked up by scintigraphy (minimum size was 1.8 cms). The T/N ratios were significantly higher in malignant lesions (average 1.65 ± 0.55, range 1.20- 4.2.) as compared to benign lesions (average 1.29 ± 0.20, range 0.9-1.7). There was a significant difference between T/N ratio of patients with malignant and non-malignant lesions (p=0.006). There was no significant difference in uptake ratios in patients of lung cancer with different histopathology (p=0.584). We conclude that semi-quantitative uptake ratios obtained by Tc99m-tetrofosmin/sestamibi lung scintigraphy are useful in differentiation of malignant from benign lung lesions. (author)