Patient characteristics
Forty-six patients with histologically confirmed PNETs were scanned with 68Ga- DOTATATE PET/MR and 18F-FDG PET/MR between April 2020 and May 2022. The patients comprised of 25 women (54.3%) and 21 men (45.7%), aged 22–75 y (median age, 52 y). There were 29 patients with G1 tumors, 14 with G2 tumors, and 3 with NEC (a more severe kind of cancer) tumors. ENET N staging for these patients was as follows: N0 (n = 39), N1 (n = 7). ENET M staging for these patients was as follows: M0 (n = 36), M1 (n = 10). Table 1 provides a summary of the patient characteristics.
Table 1
Clinical characteristics of PNET patients who underwent combined 68Ga-DOTATATE and 18F-FDG PET/MR
|
Total, (%)
|
Gender, n (%)
|
|
Female
|
25 (54.3)
|
Male
|
21 (45.7)
|
Mean age, years (range)
|
51 (22–75)
|
Primary site, n (%)
|
|
Head/neck
|
14 (30.5)
|
Body/tail
|
29(63.0)
|
Multifocal
|
3 (6.5)
|
WHO grade, n (%)
|
|
G1
|
29(63.0)
|
G2
|
14 (30.5)
|
G3-NEC
|
3(6.5)
|
ENET stage, n (%)
|
|
N stage
|
|
N0
|
39 (83.0)
|
N1
|
7(17.0)
|
M stage
|
|
M0
|
36 (76.6)
|
M1
|
10(23.4)
|
68Ga-DOTATATE, 18F-FDG PET, and MR ADC relationships
Increases in the FSUVmax, MTV, and TLG 18F-FDG PET/MR parameters were observed with increasing tumor grade from G1-G3, whereas GSUVmax values derived from 68Ga-DOTATATE PET/MR scans declined with tumor grade. SRD and TLSRD values rose with tumor grade. Significant decreases in ADCmin and ADCmean values were observed with increasing tumor grade. For further details regarding tumor characteristics, see Table 2.
Table 2
Parameters of 68Ga-DOTATATE and 18F-FDG dual tracer PET/MR based on tumor grade
Parameters
|
G1
|
G2
|
G3-NEC*
|
P (G1v G2)
|
P (G2 v NEC)
|
P (G1 v NEC)
|
FSUVmax
|
2.5(2.1–7.3)
|
5.0(2.8–9.3)
|
11.5(8.1–13.6)
|
0.04
|
0.15
|
0.05
|
MTV
|
2.3(1.1–6.1)
|
7.1(2.5–28.4)
|
68(51.6-804.3)
|
0.04
|
0.03
|
< 0.01
|
TLG
|
3.8(1.8–19)
|
24.8(4.6-129.4)
|
505.7(396.1-3168.3)
|
0.03
|
0.03
|
< 0.01
|
GSUVmax
|
60.6(37.8–99.5)
|
41.9(19.0-72.4)
|
18.5(4.5–23.4)
|
0.11
|
0.10
|
0.02
|
SRD
|
5.6(3.1–20.6)
|
12.1(6.7–44.8)
|
55.5(27.5-705.9)
|
0.11
|
0.08
|
0.02
|
TLSRD
|
121.8(60.3-427.2)
|
197.3(52.8-1392.2)
|
236(118.7-2597.1)
|
0.68
|
0.61
|
0.32
|
ADCmin
|
885.1 ± 140.4
|
703.4 ± 85.2
|
277.5 ± 79.2
|
< 0.01
|
< 0.01
|
< 0.01
|
ADCmean
|
1485.2 ± 234.4
|
1322.0 ± 301.9
|
811.9 ± 79.4
|
0.04
|
< 0.01
|
< 0.01
|
SUV: standardized uptake value; MTV: metabolic tumor volume; TLG: total lesion glycolysis; SRD: somatostatin receptor density; TLSRD: total lesion somatostatin receptor density. Values are presented as median with interquartile range (IQR) in parentheses. *Numbers in parentheses are ranges. |
Ki-67 index, 68Ga-DOTATATE, 18F-FDG PET, and ADC parameters correlate
Ki-67 index values were significantly positively correlated with FSUVmax (r = 0.45, P < 0.01), TLG (r = 0.48, P < 0.01), MTV (r = 0.42, P < 0.01), and SRD (r = 0.43, P < 0.01), whereas they were significantly negatively correlated with ADCmin (r = − 0.85, P < 0.01), GSUVmax (r = − 0.327, P = 0.03), and ADCmean (r = − 0.61, P < 0.01). Ki-67 index levels and TLSRD had a slight, nonsignificant connection (r = 0.19, P = 0.20).
Relationships between tumor staging and 68Ga-DOTATATE, 18F-FDG PET, and ADC parameters
Increases in TLG (P = 0.03), SRD (P = 0.01), decreases in ADCmin (P < 0.01), and decreases in ADCmean (P < 0.01) were all associated with increasing tumor N staging. MTV (P = 0.03), TLG values (P = 0.03), SRD (P < 0.01), ADCmin (P < 0.01), and ADCmean (P < 0.01) were linked with tumor M staging. Tumor staging was not significantly linked with any of the other examined characteristics (P > 0.05) (Table 3).
Table 3
Parameters of 68Ga-DOTATATE and 18F-FDG dual tracer PET/MR based on N stage and M stage
Parameters
|
N0
|
N1
|
P (N0 v N1)
|
M0
|
M1
|
P (M0 v M1)
|
FSUVmax
|
2.7(2.1–8.1)
|
5.9 (5.1–11.5)
|
0.07
|
2.6(2.1–11.1)
|
5.3(4.1–7.8)
|
0.17
|
MTV
|
2.6(1.2–14.1)
|
25.3 (2.5–51.6)
|
0.07
|
2.5(1.0-10.9)
|
22.1(2.5–40.0)
|
0.03
|
TLG
|
4.5(1.9–72.1)
|
96.8 (9.5-396.1)
|
0.03
|
4.3(1.8–70.9)
|
60.3(9.3–199.0)
|
0.03
|
GSUVmax
|
56.1(24.5–85.1)
|
27.8(16.1–95.1)
|
0.55
|
51.4(25.3–89.5)
|
59.7(14.3–83.0)
|
0.63
|
SRD
|
6.9(3.1–20.5)
|
30.7 (17.3–70.4)
|
0.01
|
6.2(3.0-22.7)
|
25.6(11.1–91.9)
|
< 0.01
|
TLSRD
|
121.8(59.1-328.6)
|
264.4 (118.7–849)
|
0.24
|
115.3(59.7-318.6)
|
271.7(103.3-2689.6)
|
0.17
|
ADCmin
|
840.4 ± 152.7
|
510.4 ± 216.5
|
< 0.01
|
843.0 ± 167.8
|
600.1 ± 201.8
|
< 0.01
|
ADCmean
|
1446.8 ± 283.1
|
1084.1 ± 199.6
|
< 0.01
|
1458.3 ± 282.0
|
1151.5 ± 246.2
|
< 0.01
|
Relationships between 18F-FDG PET and MR parameters
Correlation values of -0.52 (P < 0.01), -0.50 (P < 0.01), and − 0.56 (P < 0.01) were found between the 18F-FDG PET parameters FSUVmax, MTV, and TLG, respectively (Fig. 1). There was no significant association between the parameters of ADCmean and 18F-FDG PET. These findings indicate that the ADCmin and FDG parameters have a negative connection, which may be predictive of PNET grade and staging.