Gross tumor volume delineation in primary prostate cancer on 18F-PSMA-1007 PET/MRI and 68Ga-PSMA-11 PET/MRI

A total of 69 patients were enrolled in this study, 57 of whom underwent 18F-PSMA-1007 PET/MRI and 12 of whom underwent 68Ga-PSMA-11 PET/MRI. Therefore, based on different PET tracers, patients were divided into 2 groups: the 18F subgroup and 68Ga subgroup. The patients’ characteristics and volumetric results are displayed in Table 1.

Table 1 Patient characteristics and volumetric results

The GTV-MRI, GTV-PETVIS, and GTV-PET/MRI delineated by the visual method from different observers are shown in Table 2. The DSC between GTVs delineated by observers A, B, and C is displayed in Table 3. There were no significant differences in tumor volume delineated by different observers.

Table 2 GTVs obtained by three observers in 18F and 68Ga subgroupsTable 3 DSC between GTVs delineated by observers A, B and C in the 18F and 68Ga subgroups 18F subgroup results

Statistical analysis showed that GTV-PET50% (r = 0.338, p < 0.05), GTV-PET60% (r = 0.317, p < 0.05), GTV-PETVIS (r = 0.742, p < 0.001) and GTV-PET/MRI (r = 0.923, p < 0.001) were significantly related to the reference GTV-MRI. GTV-PET/MRI (p < 0.001), GTV-PET30% (p < 0.001), GTV-PET40% (p < 0.05), and GTV-PET60% (p < 0.05) diverged such that differences were statistically significant from the referenced GTV-MRI results (Fig. 3, A).

Fig. 3figure 3

The GTV volumes of the 18F subgroup (A) and the 68Ga subgroup (B). Each item and its longitudinal extension represent the median (IQR) of the GTVs. *p < 0.05, *** p < 0.001

The average DSC between GTV-MRI and GTV-PETVIS was 0.45 (range 0–0.86), that between GTV-MRI and GTV-PET/MRI was 0.71 (range 0–0.99), that between GTV-MRI and GTV-PET30% was 0.32 (range 0–0.80), that between GTV-MRI and GTV-PET40% was 0.33 (range 0–0.75), that between GTV-MRI and GTV-PET50% was 0.30 (range 0–0.71), and that between GTV-MRI and GTV-PET60% was 0.23 (range 0–0.70). We selected the DSC between GTV-MRI and GTV-PET/MRI, since it was greater than 0.7, to evaluate the correlation with the reference GTV-MRI (r = 0.516, p < 0.001), PSA (r = 0.288, p < 0.05), risk classification (r = 0.287, p < 0.05), and Gleason score (r = 0.321, p < 0.05) (Fig. 4). GTV-MRI significantly and positively affected the DSC (r2 = 0.462, p < 0.05). Age, PSA level, Gleason score, SUVmax, and risk classification showed no linear correlation with the degree of concordance between the imaging modalities.

Fig. 4figure 4

The correlation between DSC (between GTV-MRI and GTV-PET/MRI) and the reference GTV-MRI (r = 0.516, p < 0.001), PSA (r = 0.288, p < 0.05), risk classification (r = 0.287, p < 0.05), and Gleason score (r = 0.321, p < 0.05) in the 18F subgroup

A total of 40 patients in the 18F group underwent radical prostatectomy within one month after the PET/MRI scan. The Lpath, LPET/MRI, LMRI, LPET, LPET30%, LPET40%, LPET50% and LPET60% were 1.74 (1.34–2.31) cm, 1.75 (1.41–2.41) cm, 1.41 (1.05–1.92) cm, 1.55 (1.15–2.00) cm, 2.68 (1.94–3.32) cm, 2.10 (1.49–2.59) cm, 1.64 (1.24–2.27) cm, and 1.41 (0.84–1.73) cm, respectively.

The results showed that LPET/MRI (r = 0.893, p < 0.001), LMRI (r = 0.797, p < 0.001), and LPET (r = 0.888, p < 0.001) were significantly correlated with the gold standard Lpath. LPET/MRI had the highest consistency with the gold standard Lpath (ICC = 0.893, 95% CI: 0.806–0.942, p < 0.001) (Table 4). According to the Bland–Altman diagram, the mean of the difference between LPET/MRI and Lpath was -0.029, the 95% limit of agreement was -0.673 ~ 0.616, and only one case was outside the limit, which indicates a good consistency level of these data (Fig. 6, A).

Table 4 ICC consistency between Lpath and tumor lengths obtained by different methods 68Ga subgroup results

Statistical analysis showed that GTV-PET30% (r = 0.629, p < 0.05), GTV-PET40% (r = 0.581, p < 0.05), GTV-PETVIS (r = 0.595, p < 0.05) and GTV-PET/MRI (r = 0.944, p < 0.001) were significantly related to the reference GTV-MRI. GTV-PET/MRI (p < 0.05) and GTV-PET30% (p < 0.05) diverged statistically significantly from the reference GTV-MRI results (Fig. 3, B).

The average DSC value between GTV-MRI and GTV-PETVIS was 0.33 (range 0.08–0.55), that between GTV-MRI and GTV-PET/MRI was 0.72 (range 0.4–0.96), that between GTV-MRI and GTV-PET30% was 0.33 (range 0.09–0.82), that between GTV-MRI and GTV-PET40% was 0.33 (range 0.06–0.73), that between GTV-MRI and GTV-PET50% was 0.27 (range 0.04–0.59), and that between GTV-MRI and GTV-PET60% was 0.19 (range 0–0.38). We chose the DSC between GTV-MRI and GTV-PET/MRI, since it was greater than 0.7, to assess the correlation with the reference GTV-MRI (r = 0.580, p < 0.05) (Fig. 5). None of the variables was significantly associated linearly with the degree of concordance.

Fig. 5figure 5

The correlation between DSC (between GTV-MRI and GTV-PET/MRI) and the reference GTV-MRI (r = 0.580, p < 0.05) in the 68Ga subgroup

A total of 11 patients in the 68Ga group underwent radical prostatectomy within one month after the PET/MRI scan. The Lpath, LPET/MRI, LMRI, LPET, LPET30%, LPET40%, LPET50% and LPET60% were 1.61 (1.38–1.99) cm, 1.37 (1.24–1.29) cm, 1.33 (1.02–2.07) cm, 1.32 (1.10–2.11) cm, 1.54 (1.32–3.22) cm, 1.41 (1.11–2.69) cm, 1.54 (0.74–2.45) cm, 1.21 (0.69–1.78) cm, respectively.

The results showed that LPET/MRI (r = 0.848, p < 0.001), LMRI (r = 0.831, p < 0.01), LPET (r = 0.761, p < 0.01), LPET40% (r = 0.717, p < 0.05) and LPET50% (r = 0.639, p < 0.05) were significantly correlated with the gold standard Lpath. LPET/MRI had the highest consistency with the gold standard Lpath (ICC = 0.837, 95% CI: 0.505–0.953, p < 0.001) (Table 4). According to the Bland–Altman diagram, the mean of the difference between LPET/MRI and Lpath was 0.046, the 95% limit of agreement was -0.803 ~ 0.896, and only one case was outside the limit, which indicates a good consistency level of these data (Fig. 6, B).

Fig. 6figure 6

Bland–Altman plots of LPET/MRI and Lpath in the 18F subgroup (A) and the 68Ga subgroup (B)

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