The role of metabolic parameters obtained by FDG PET/CT in predicting treatment response in patients with colorectal carcinoma.

Purpose: In patients diagnosed with colorectal carcinoma who had elevated serum tumor markers at the time of diagnosis and in whom these markers were used in followup, we aimed to investigate whether there is a correlation between markers and semiquantitative-metabolic parameters (SUVmax, SUVmean, MTV, TLG) obtained from primary tumor and metastases with 18F-FDG PET/CT and which metabolic parameter is more sensitive in predicting response to treatment. Materials and Methods: We retrospectively analyzed 66 patients who were admitted to Dicle University Faculty of Medicine, Department of Nuclear Medicine between May 2018 and September 2023 and underwent 18F-FDG PET/CT studies for staging, treatment response and re-staging in our department and who had not undergone surgery for primary tumor. We compared the semiquantitative-metabolic parameters (SUVmax, SUVmean, PT-MTV, PT-TLG, PT-TLG, WB-MTV, WB-TLG) and serum tumor markers (CEA, CA 19-9) obtained from two consecutive F18-FDG PET/CT studies with a threshold of 40% and manual drawings. Results: According to two consecutive 18 F-FDG PET/CT results, we divided our study group into two groups as regression group (n=45) and progression group (n=21). In the regressed patient group, there was a high positive correlation between WB-TLG and serum tumor marker (r=0.618, p=0.000), a moderate positive correlation between SUVmax and PT-TLG and serum tumor marker (r=0497, p=0.001; r=0.511, p=0.000), and a weak positive correlation between SUVmean and WB-MTV and serum tumor marker (r=0.435, p=0.003). There was a moderate positive correlation between WBTLG and serum tumor marker in the progression group (r=0.596, p=0.004). There was a weak positive correlation between SUVmax, SUVmean, TLG, WB-MTV and serum tumor marker in the progression group (r=0,343, p=0.128; r=0.299, p:0.188; r=0.279, p=0.220; r=0.374 p=0.095). Conclusion: We concluded that FDG PET/CT will be of great benefit in the evaluation of treatment response as well as in the detection of recurrent disease in patients with 4 colorectal carcinoma and in this context, especially WB-TLG value is the most sensitive parameter that can be an alternative to SUVmax in predicting treatment response. Keywords: Colorectal Carcinoma, 18F-FDG, PET/CT, TLG, MTV