A visual and semi-quantitative assessment of (99m)Tc-EDDA/HYNIC-TOC scintigraphy in differentiation of solitary pulmonary nodules.

BACKGROUND
The aim of the study was the assessment of the clinical usefulness of scintigraphy with (99m)Tc-EDDA/HYNIC-TOC for purposes of a differential diagnosis of SPNs by means of a visual inspection and semi-quantitative assessment of uptake intensity of the radiopharmaceutical (RPh).


MATERIAL AND METHODS
In 53 patients (32 males and 21 females at the ages between 38 and 78 years, mean value 57) with SPN on chest radiographs or CT scans, of diameters from 1 to 5.5 (mean 2.3) cm a SPECT acquisition was performed, 2-4 h after administration of 740 MBq of RPh. Additionally, aiming at the implementation of a correction of a partial volume effect resulting from finite resolution of this technique, the measurement of the resolution of this technique was performed on an thorax phantom. Scintigraphic studies were inspected visually visually and semi-quantitatively, restoring real concentration of the RPh in nodules in comparison with the peritumoral background (tumour-to-background ratio) by the application of resolution recovery coefficients for the respective nodule diameters. The threshold values of tumour-to-background ratio providing optimal differentiation between malignant and benign nodules of sizes smaller and larger than 2 cm in diameter were determined. Verification of scintigraphic results was based on pathological examinations of tumour samples (histopathology or cytology) and in some cases on bacteriological studies. The additional criterion of tumour benignity was accepted, based on its stable size in a time interval no shorter than 3 years.


RESULTS
In 32 patients the following malignant tumours were diagnosed: 12 adenocarcinomas, 6 squamous cell carcinomas, 6 non-small cell lung cancers of unspecified more detailed morphology, 2 large cell carcinomas, 2 small cell lung cancers, 2 carcinoids and 2 metastatic lesions (malignant melanoma and leiomyosarcoma). In 21 patients benign etiologies were found: 6 tuberculomas, 2 other granuloma, 4 hamartomas, 2 non-specific inflammatory infiltrate, 1 alien body with inflammatory reaction and 1 suppurating inflammatory lesion, 1 abscesses, 1 peripheral carcinoid of morphological features of a benign tumour, 2 tumours of unspecified etiology with sizes stable over 3 and 5 years, and 1 ectopic lesion of thyroid tissue. A visual inspection of scintigrams revealed enhanced uptake of RPh at 29 of 32 sites corresponding to locations of malignant nodules, in 2 cases (1 adenocarcinoma and 1 metastatic lesion of malignant melanoma) results were negative and in 1 (metastatic leiomyosarcoma) equivocal; in 13 of 21 benign nodules true negative results were obtained, in 4--positive (foreign body with inflammatory reaction, abscess, suppurating inflammatory lesion and tuberculoma), in the next 4--equivocal (2 tuberculomas, 1 hamartoma, 1 tumour of unspecified aetiology, but with a stable size over 3 years). The mean values of tumour-to-back-ground ratio without resolution recovery in malignant and benign nodules equalled 4.6 (sd 5.9) and 1.8 (sd 1.2), resp. (p = 7 x 10(-4)), while after resolution recovery coefficients--7.8 (sd 7.2) and 2.7 (sd 2.8), resp. (p = 2 x 10(-4)). The semi-quantitative method resulted in true positive results in 29/32 malignant cases and true negative in 15/21 benign cases.


CONCLUSIONS
(99m)Tc-EDDA/HYNIC-TOC scintigraphy is a very promising method for the differentiation of SPNs. The semi-quantitative method using resolution recovered tumour-to-background ratio enables the differentiation of malignant and benign SPNs based on the intensity of RPh uptake and facilitates the making of a decision as to the positive or negative scintigraphic character of the equivocal lesions.