**2. Results**

## *2.1. Overall Lesion Positivity Rate*

A positivity rate in 147 out of 215 restaging patients (68%) (mean prostate-specific antigen (PSA) serum level 19.2 ± 82.5 ng/mL) and in 13 out of 18 primary staging patients (72%) (mean PSA 39.1 <sup>±</sup> 67.5 ng/mL) was shown by [68Ga]Ga-PSMA-11 PET/CT. At least one lesion suspect for malignancy was detected in these patients. This retrospective study includes 147 restaging patients (prostatectomized patients (P-P) and irradiated patients (P-I)) and 13 staging patients (patients suspected of having primary PCa (P-T)), both with PSMA-positive findings (Table 1). To ensure accurate statistical analysis and a homogenous patient population, the biochemically recurrent (BC)-patients, previously treated by radical prostatectomy (patient group P-P) and those previously treated by irradiation (patient group P-I) were separately evaluated according to the definition protocol of BC patients [15].


**Table 1.** Patient characteristics.

Abbreviations: PSA, prostate-specific antigen; SD, standard deviation; *n*, number of patients; y, year.

2.1.1. Lesion Positivity Rate Post-Prostatectomized (P-P)

• Baseline: 551 lesions in 114 patients

In this subgroup (P-P and baseline PET/CT), the detection efficacy was 27% (33) for PSA levels of 0.2 to <0.5 ng/mL and 32% (25), 70% (27), 77% (43), and 90% (50) for PSA levels of 0.5 to <1 ng/mL, 1 to <2 ng/mL, 2 to <5 ng/mL, and ≥5 ng/mL, respectively (*p* < 0.001) (Table 2).

Patients with a PSMA-positive scan showed local recurrence in 24% (27/114) and metastases in 90%. Of the patients with metastases, 39% exhibited local metastases and 30% exhibited distant metastases, and 31% showed both. In 70% of the patients, LNM were detected, 78% of which were pelvic LNM (Table 2).

• Delayed: 554 lesions in 114 patients

Late imaging (3 h after intravenous injection (p.i.)) showed no difference in the detection efficacy when considering the patients without separate division of the number of lesions (Table 2).


**Table 2.** PET/CT findings: Lesion positivity rate (LPR) post-prostatectomized (P-P) related to different PSA values.

\* Fisher's exact test. Abbreviations: PSA, prostate-specific antigen; LNM, lymph node metastases; *p* < 0.05 is considered significant; *r*, Pearson correlation coefficient.

#### 2.1.2. Lesion Positivity Rate Post-Irradiated (P-I)

• Baseline: 186 lesions in 33 patients

This subgroup (P-I and baseline PET/CT) showed a detection efficacy rate of 100% for PSA levels of 2 to <5 ng/mL and 94% for PSA levels of ≥5 ng/mL, respectively. Local recurrence was detected in 79% and metastases were detected in 67%. A total of 42% of the patients showed LNM, while 80% of them showed pelvic LNM. Due to the small number of patients, a statistical analysis would not have given meaningful results.

• Delayed: 187 lesions in 33 patients

The detection efficacy rates 3 h p.i. showed the same results as baseline images.

2.1.3. Lesion Positivity Rate Pre-Therapy (P-T)

All patients (13) with PSMA-positive lesions showed histopathologically (biopsy-proven) adenocarcinoma PCa.

• Baseline: 47 lesions in 13 patients

In this subgroup (P-T and baseline PET/CT), the detection efficacy was shown in 69% for PSA levels of >4 to <50 ng/mL and in 100% for PSA levels of ≥50 ng/mL. Primary tumor lesions in the prostate were detected in 100%, metastases were detected in 38%, and LNM were detected in 31%, of which pelvic LNM were shown in 75%. Statistical analysis was not done due to the small patient number.

• Delayed: 47 lesions in 13 patients

No difference in the detection efficacy was shown in late compared to baseline imaging.
