Fifty-three patients with NSCLC were included in the study; 50 were male, and three were female. The mean age was 68.1±9.8 years. Seven patients underwent only RT [four patients were not a candidate for chemotherapy due to comorbid diseases, concomitant chemotherapy was not given to 2 patients due to chemotherapy toxicity, one patient refused chemotherapy treatment) furthermore, 46 patients received CRT. Patient characteristics are given in table 1. Twenty-one patients were adenocarcinoma, and 32 were squamous cell carcinoma (SCC). All parameters were independent of histopathological subtype. Tumor characteristics were given in table 2. Pre and post-RT SUV, GTVPET-CT, and MTV values were given in Table 3.
We analyzed whether there was any difference between pre-treatment SUVmax, GTVPET-CT, MTV and tumor size values between patient groups with and without post-RT residual disease. In the patient group with post-RT residual disease, pre-RT SUVmax (p = 0.019, Z = -2.342), GTVPET-CT (p = 0.007, Z = -2.674), MTV (p = 0.048, Z= -1.974), tumor size (p = 0.011, Z = -2.531) values were statistically significantly higher than the patient group without post-RT residual disease (Table 4).
Fifteen patients had PETNECROSIS (4 adenocarcinomas, 11 SCC). We calculated the percentage of necrosis in 14 patients (27.36 ± 8.94%, range: 13-43). Of all six patients with a necrosis percentage, ≥ 30% had residual disease on post-RT 18F FDG PET/CT, 5 of 8 patients with necrosis <30% had residual disease, and 3 had no residual disease on post-RT 18F FDG PET/CT.
Increased tumor size was associated with the presence of PETNECROSIS. There was a statistically significant relationship between tumor size and PETNECROSIS presence/absence (p= 0.009, OR: 1.036, 95CI%: 1.009-1.064). Using the ROC curve, we divided patients into two groups according to tumor size (<44.5mm vs ≥44.5mm, sensitivity: 80%, specificity: 60.9%, AUC = 0.755, 95CI% 0.614-0.897, p = 0.004). Presence of PETNECROSİS was statistically significantly different between the groups with tumor size <44.5mm and ≥44.5mm [p = 0.012, Odds ratio (OR): 6.133, 95CI%: 1.479-25.440]. Using the ROC curve, we divided patients into two groups based on the GTVPET-CT (<47.5 mL vs ≥47.5 mL, sensitivity: 80%, specificity: 77.1%, AUC = 0.775, 95CI%: 0.635-0.916, p = 0.002). Presence of PETNECROSİS was statistically different between the groups with GTVPET-CT <47.5 mL vs ≥47.5 mL (p = 0.002, OR: 9.818, 95CI%: 2.311-41.706).
By using ROC curve, we determined threshold values for 18F FDG PET/CT parameters according to optimal sensitivity-specificity values. We divided the patients into two groups according to the threshold values and included them in the univariate logistic regression analysis. GTVPET-CT ≤ 28.25 mL vs >28.25 mL (Sensitivity, 76.7%, spesifitivity 60.1%, AUC=0.716, p= 0.007, 95CI%: 0.575-0.857), tumor size ≤43mm vs >43mm (Sens:70%, spes:60.1%, AUC=0.704, p=0.011, 95CI%: 0.562-0.847), MTV ≤ 22.85 mL vs >22.85 mL (Sens:60%, spes:60.1%, AUC=0.659, p=0.048, 95CI%=0.512-0.807), SUVmax ≤11.6 vs>11.6 (Sens: 76.7%, spes: 65.2%, p= 0.019, AUC=0.689, 95CI%: 0.542-0.837) were determined.
In univariate logistic regression analysis; SUVmax ≤11.6vs>11.6 (p=0.003, OR:6.161, 95CI%:1.846-20.557), tumor size ≤43mm vs >43mm (p=0.027, OR:3.630, 95CI%:1.155-11.406), GTVPET-CT ≤ 28.25 mL vs >28.25 mL (p=0.007, OR:5.111, 95CI%:1.554-16.807) and PETNECROSİS (p=0.039, OR:4.444, 95CI%:1.078-18.321) were statisticaly significant predictors for CMR. MTV ≤ 22.85 mL vs >22.85 mL (p=0.135, OR:2.333, 95CI%:0.768-7.089), radiation dose (p=0.263, OR:1.108, 95CI%: 0.926-1.326) and histology (p=0.285, OR:1.833, 95CI%:0.601-5.597) were not statistically significant predictors of CMR.
Multivariate logistic regression analysis demonstrated that, SUVmax ≤11.6 vs >11.6 (p=0.003, OR:7.670, 95CI%:2.013-29.231) and PETNECROSİS (p=0.028, OR:6.704, 95CI%1.214-30.394) were independent predictors for CMR. Table 5.