**3. Results**

In 12/21 DLBCL patients (57%), CR was observed after CAR-T cell therapy, whereas 9/21 patients (43%) showed PR. No patient had a progression at first follow-up after CAR-T cell therapy.

#### *3.1. Quantitative Analysis of Tumor Volumetric Parameters*

The whole-body MTV and whole-body TLG differed significantly (*p* < 0.01 and *p* < 0.05, respectively) between the subgroups assigned to CR or PR showing lower levels in the CR group at baseline (MTV: 35 ± 38 mL vs. 88 ± 110 mL; TLG: 319 ± 362 vs. 1488 ± 2254) (Figure 1).

**Figure 1.** (**a**) At baseline 18F-FDG PET/CT before CAR-T cell therapy, both the whole-body MTV (35 ± 38 mL vs. 88 ± 110 mL) and (**b**) the whole-body TLG (319 ± 362 vs. 1488 ± 2254) were lower in patients achieving CR compared to patients achieving PR (*p* < 0.01 and *p* < 0.05). The asterisk (\*) indicates clinical significance (*p* < 0.05).

In the entire patient cohort, a significant (*p* < 0.01) decrease was observed for wholebody MTV (62 ± 86 mL vs. 4 ± 5 mL) and whole-body-TLG (925 ± 1722 vs. 33 ± 59) (Figure 2). After CAR-T cell therapy, MTV and TLG were not measurable in the subgroup achieving CR, whereas in the subgroup with PR, MTV (88 ± 110 mL vs. 7 ± 4 mL) and TLG (1488 ± 2254 vs. 41 ± 39) significantly decreased (*p* < 0.01).

**Figure 2.** (**a**) Whole-body MTV at baseline 18F-FDG-PET/CT before CAR T cell therapy (62 <sup>±</sup> 86 mL) and at first follow-up 18F-FDG-PET/CT (4 <sup>±</sup> 5 mL) after CAR T cell therapy in the entire patient cohort (*p* < 0.01). (**b**) Whole-body TLG at baseline 18F-FDG-PET/CT before CAR-T cell therapy (925 <sup>±</sup> 1722) and at first follow-up 18F-FDG-PET/CT (33 <sup>±</sup> 59) after CAR-T cell therapy in the entire patient cohort (*p* < 0.01). The asterisk (\*) indicates clinical significance (*p* < 0.05).

#### *3.2. CT-Texture Analysis*

At baseline, the "entropy" proved lower (1.81 ± 0.1) in patients achieving CR compared to patients achieving PR (2.08 ± 0.2; *p* < 0.05) (Figure 3a). In contrast, the "uniformity" was higher in patients with CR (0.33 ± 0.02) compared to patients with PR (0.28 ± 0.47; *p* < 0.05) (Figure 3b). No significant differences were found for "skewness" (0.11 ± 0.21 [CR] vs. −0.32 ± 1.23 [PR]; *p* > 0.05) and "mean" (66.1 ± 18.89 [CR] vs. 49.3 ± 23.9 [PR]; *p* > 0.05) with a trend in "mean" for higher values in patients with CR.

**Figure 3.** (**a**) Entropy at baseline imaging before CAR-T cell therapy in patients achieving CR (1.81 ± 0.1) vs. PR (2.08 ± 0.2; *p* < 0.05). (**b**) Uniformity at baseline imaging before CAR-T cell therapy in patients achieving CR (0.33 ± 0.02) vs. PR (0.28 ± 0.47; *p* < 0.05). The asterisk (\*) indicates clinical significance (*p* < 0.05).
