A Prospective Study Comparing Functional Imaging (18F-FDG PET) Versus Anatomical Imaging (Contrast Enhanced CT) in Dosimetric Planning for Non-small Cell Lung Cancer

OBJECTIVES 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET-CT) is a well-used and established technique for lung cancer staging. Radiation therapy requires accurate target volume delineation, which is difficult in most cases due to coexisting atelectasis. The present study was performed to compare the 18F-FDG PET-CT with contrast enhanced computed tomography (CECT) in target volume delineation and investigate their impacts on radiotherapy planning. METHODS Eighteen patients were subjected to 18F- FDG PET-CT and CECT in the same position. Subsequently, the target volumes were separately delineated on both image sets. In addition, the normal organ doses were compared and evaluated. RESULTS The comparison of the primary gross tumour volume (GTV) between the 18F-FDG PET-CT and CECT imaging revealed that 88.9% (16/18) of the patients had a quantitative change on the 18F-FDG PET-CT. Out of these patients, 77% (14/18) of the cases had a decrease in volume, while 11% (2/18) of them had an increase in volume on the 18F-FDG PET-CT. Additionally, 44.4% (8/18) of the patients showed a decrease by > 50 cm 3 on the 18F-FDG PET-CT. The comparison of the GTV lymph node between the 18F-FDG PET-CT and CECT revealed that the volume changed in 89% (16/18) of the patients: it decreased and increased in 50% (9/18) and 39% (7/18) on the 18F-FDG PET-CT. New nodes were identified in 27% (5/18) of the patients on the 18F-FDG PET-CT. The decrease in the GTV lymph node on the 18F-FDG PET-CT was statistically significant. The decreased target volumes made radiotherapy planning easier with improved sparing of normal tissues. CONCLUSION GTV may either increase or decrease with the 18F-FDG PET-CT, compared to the CECT. However, the 18F-FDG PET-CT-based contouring facilitates the accurate delineation of tumour volumes, especially at margins, and detection of new lymph node volumes. The non-FDG avid nodes can be omitted to avoid elective nodal irradiation, which can spare the organs at risk and improve accurate staging and treatment.