99mTc-MIBI scintigraphy for early detection of locally recurrent non-small cell lung cancer treated with definitive radiation therapy

After radiation therapy of lung cancer, a dense fibrotic shadow develops in the irradiated lung. Owing to this fibrosis, early detection of local recurrence after treatment is sometimes difficult even when using computed tomography (CT) and magnetic resonance imaging. We investigated the diagnostic accuracy of technetium-99m hexakis 2-methoxyisobutylisonitrile (Tc-99m-MIBI) scintigraphy for the detection of recurrent lung cancer following definitive radiation therapy. Eighteen patients with primary non-small cell lung cancer treated with radiation therapy 1 year previously were studied with Tc-99m-MIBI scintigraphy. They showed no evidence of local recurrence on serial chest radiographs. All single-photon emission tomography (SPET) images acquired 2 h after intravenous administration of the radiopharmaceutical were visually interpreted with knowledge of the pretreatment chest radiograph, CT and the details of radiation therapy (radiation portals and administered doses). A region of interest (ROI) analysis was also performed. In addition to the ROI ratio of tumour uptake to accumulation in contralateral normal lung (tumour/lung ratio), another semiquantitative analysis, the ratio of tumour uptake to accumulation in radiation fibrosis (tumour/fibrosis ratio), was performed to differentiate between accumulation in radiation fibrosis and the tumour uptake. The scintigraphic diagnoses were correlated with clinical outcome. The sensitivity, specificity and negative predictive value of Tc-99m-MIBI scintigraphy for the detection of recurrent lung cancer were all 88.9% (8/9). The tumour/lung ratios (mean+/-SEM) of the nine patients with local recurrence and the other eight without local failure were 2.00+/-0.11 and 1.40+/-0.09, respectively (P<0.01). The tumour/fibrosis ratios of the patients with and those without recurrence were 1.47+/-0.08 and 0.93+/-0.05, respectively (P<0.01). These results suggest that Tc-99m-MIBI scintigraphy might be of value for the detection of recurrent lung cancer, and especially of small foci in areas of radiation fibrosis that are hardly noticeable on serial chest radiographs.