Evaluation of gross tumor size using CT, 18F-FDG PET, integrated 18F-FDG PET/CT and pathological analysis in non-small cell lung cancer

PURPOSE: The correlation of gross tumor sizes between combined 18F-FDG PET/CT images and macroscopic surgical samples has not yet been studied in detail. In the present study, we compared CT, 18F-FDG PET and combined 18F-FDG PET/CT for the delineation of gross tumor volume (GTV) and validated the results through examination of the macroscopic surgical specimen.

METHODS: Fifty-two operable non-small cell lung cancer (NSCLC) patients had integrated 18F-FDG PET/CT scans preoperatively and pathological examination post-operation. Four separate maximal tumor sizes at X (lateral direction), Y (ventro-dorsal direction) and Z (cranio-caudal direction) axis were measured on 18F-FDG PET, CT, combined 18F-FDG PET/CT and surgical specimen, respectively. Linear regression was calculated for each of the three imaging measurements versus pathological measurement.

RESULTS: No significant differences were observed among the tumor sizes measured by three images and pathological method. Compared with pathological measurement, CT size at X, Y, Z axis was larger, whereas combined 18F-FDG PET/CT and 18F-FDG PET size were smaller. Combined 18F-FDG PET/CT size was more similar to the pathological size than that of 18F-FDG PET or CT. Results of linear regressions showed that integrated 18F-FDG PET/CT was the most accurate modality in measuring the size of cancer.

CONCLUSIONS: 18F-FDG PET/CT correlates more faithfully with pathological findings than 18F-FDG PET or CT. Integrated 18F-FDG PET/CT is an effective tool to define the target of GTV in radiotherapy.