Feasibility of Pathology-Correlated Lung Imaging for Accurate Target Definition of Lung Tumors

Purpose To accurately define the gross tumor volume (GTV) and clinical target volume (GTV plus microscopic disease spread) for radiotherapy, the pretreatment imaging findings should be correlated with the histopathologic findings. In this pilot study, we investigated the feasibility of pathology-correlated imaging for lung tumors, taking into account lung deformations after surgery. Methods and Materials High-resolution multislice computed tomography (CT) and positron emission tomography (PET) scans were obtained for 5 patients who had non–small-cell lung cancer (NSCLC) before lobectomy. At the pathologic examination, the involved lung lobes were inflated with formalin, sectioned in parallel slices, and photographed, and microscopic sections were obtained. The GTVs were delineated for CT and autocontoured at the 42% PET level, and both were compared with the histopathologic volumes. The CT data were subsequently reformatted in the direction of the macroscopic sections, and the corresponding fiducial points in both images were compared. Hence, the lung deformations were determined to correct the distances of microscopic spread. Results In 4 of 5 patients, the GTVCT was, on average, 4 cm3 (∼53%) too large. In contrast, for 1 patient (with lymphangitis carcinomatosa), the GTVCT was 16 cm3 (∼40%) too small. The GTVPET was too small for the same patient. Regarding deformations, the volume of the well-inflated lung lobes on pathologic examination was still, on average, only 50% of the lobe volume on CT. Consequently, the observed average maximal distance of microscopic spread (5 mm) might, in vivo, be as large as 9 mm. Conclusions Our results have shown that pathology-correlated lung imaging is feasible and can be used to improve target definition. Ignoring deformations of the lung might result in underestimation of the microscopic spread.