Morphologic and Metabolic Comparison of Treatment Responsiveness with 18Fludeoxyglucose-Positron Emission Tomography/Computed Tomography According to Lung Cancer Type

OBJECTIVE: The aim of the present study was to evaluate the response to treatment by histopathologic type in patients with lung cancer and under follow-up with 18F-fluoro-2deoxy-glucose-positron emission tomography/computed tomography (18F-FDG PET/CT) imaging by using Response Evaluation Criteria in Solid Tumors (RECIST) and European Organisation for Research and Treatment of Cancer (EORTC) criteria that evaluate morphologic and metabolic parameters. METHODS: On two separate (pre- and post-treatment) 18F-FDG PET/CT images, the longest dimension of primary tumor as well as of secondary lesions were measured and sum of these two measurements was recorded as the total dimension in 40 patients. PET parameters such as standardized uptake value (SUVmax), metabolic volume and total lesion glycolysis (TLG) were also recorded for these target lesions on two separate 18F-FDG PET/CT images. The percent (%) change was calculated for all these parameters. Morphologic evaluation was based on RECIST 1.1 and the metabolic evaluation was based on EORTC. RESULTS: When evaluated before and after treatment, in spite of the statistically significant change (p<0.05) in SUVmax, the change was not significant in TLG, in the longest total size and in the longest size (p>0.05). In histopathologic typing, when we compare the post-treatment phase change with the treatment responses of RECIST 1.1 and EORTC criteria; for RECIST 1.1 in squamous cell lung cancer group, progression was observed in sixteen patients (57%), stability in seven patients (25%), partial response in five patients (18%); and for EORTC progression was detected in four patients (14%), stability in thirteen patients (47%), partial response in eleven patients (39%), in 12 of these patients an increase in stage (43%), in 4 of them a decrease in stage (14%), and in 12 of them stability in stage (43%) were determined. But in adenocancer patients (n=7), for RECIST 1.1, progression was determined in four patients (57%), stability in two patients (29%), partial response in one patient (14%); for EORTC, progression in one patient (14%), stability in four patients (57%), partial response in two patients (29%) were observed and in these patients, an increase in stage was detected in 3 of them (43%), while 4 of them remained stable. According to histopathologic diagnosis, between squamous cell cancer and adenocancer cases, no significant difference was determined in terms of SUVmax (p>0.05). Post-treatment SUVmax was significantly different in primary tumor but was not significantly different in nodal involvement and metastatic lesions for squamous cell carcinoma patients as compared to the pre-treatment SUVmax measurements. Similarly, there was no significant difference between primary tumor and nodal involvement for adenocarcinoma patients. CONCLUSION: Whether metabolic or morphologic changes are more accurate in evaluating treatment response in lung cancer remains unknown, and there is no gold standard diagnostic method on this issue yet. The most reliable results can only be achieved by survival curve parameters. However, we believe SUVmax seems to provide more easy and practical data for the evaluation of treatment response.