Computed Tomographic–Pathologic Correlation of Gross Tumor Volume and Clinical Target Volume in Non–Small Cell Lung Cancer

Context.—Computed tomographic (CT) scan data are used regularly in radiation treatment planning for patients with lung cancer. To our knowledge, the relationship of the CT images of tumors and their corresponding microscopic extent has not yet been studied in detail. Objective.—To correlate tumor sizes on CT with tumor sizes measured microscopically (ie, the gross tumor volume [GTV]-clinical target volume margin) in non–small cell lung cancers. Design.—Prospective pilot study. Setting.—Single institution. Patients.—Patients with operable non–small cell lung cancer were identified preoperatively. Interventions.—Once the surgical specimen was available, it was oriented with the surgeon and the pathologist. Seven whole-mount, cross-sectional histologic glass slides were made from 5 tumors using formalin fixation and hematoxylin-eosin staining. The pathologist then outlined the cancer-containing area under the microscope (Micro-GTV) and the area of surrounding inflammatory response (Micro-GTV + inflammation). Preoperative CT scans were used for outlining tumor on the corresponding slice (CT-GTV). Main Outcome Measures.—Correlation of the areas of Micro-GTV, Micro-GTV + inflammation, and CT-GTV was performed. Results.—There was an obvious trend that the CT-GTV was bigger than the Micro-GTV, except in specimen 1, in which the 2 areas were about equal. However, on comparing the values for the CT-GTV and the Micro-GTV + inflammation, the difference between the 2 areas became smaller. Conclusions.—Modern CT scans might overestimate the GTV in non–small cell lung cancer. The GTV–clinical target volume margin could actually be zero or even a negative value. The findings in this small study are interesting and provoking. Further study with a larger number of patients and more rigid quality control is warranted to confirm our findings.