Abstract
P1241
Introduction: PSMA-ligand PET has become the first-line imaging tool for staging and re-staging patients with prostate cancer. However its role in patients with prostate cancer who underwent focal therapy (HIFU, irreversible electroporation, photodynamic therapy, cryoablation, and laser therapy) is still unknown. In this study, we aimed to investigate the diagnostic performances of PSMA PET/CT to detect and localize biochemical recurrence after focal therapy.
Methods: This was a retrospective single center study. Patients with the following inclusion criteria were included: focal treatment for prostate cancer (i.e. HIFU, irreversible electroporation, photodynamic therapy, cryoablation, and laser therapy), 68Ga-PSMA-11 PET with contrast enhanced CT performed for biochemical recurrence, and no therapy between focal therapy and PET. Three independent blinded readers performed the PET image analysis and a per-region (T, N, M1a, M1b, M1c) centralized majority rule was applied (positivity rate). Inter-reader agreement of the positivity rates was calculated with Fleiss’ kappa. In a sub-cohort of patients with a biopsy performed within 3 months after the PET, diagnostic accuracy parameters (Se, Spe, PPV, NPV) were calculated on a per-patient and per-segment analysis. Twelve prostatic segments were defined, and for every segment suspicion for recurrence was assessed. SUV of suspected lesions were measured on standard +60 minutes and delayed +90 minutes acquisition. Clinically significant prostate cancer (csPCa) was considered ISUP ≥2.
Results: On the 3329 patients screened with either a PSMA PET scan or Focal Therapy performed at UCLA, 100 patients met the inclusion criteria. Median age was 69 (range 63-76). 55% patients had a pre-therapy ISUP of 2-3. Pre-therapy Median PSA was 8.4 ng/mL (range 5.4-13). 53/100 (53%) of patients were treated with HIFU, whereas 37/100 (37%) with cryoablation. PSMA-PET positivity rate per majority rule was 85/100 (85%) for prostate, 20/100 (20%) for lymph nodes and 8/100 (8%) for bone/visceral metastases. The inter-reader agreement for positivity rate by region was moderate (kappa=0.495). Perfect agreement was seen in 76 patients. 36 patients had a post-therapy biopsy data available. The median time interval from therapy and from PET was 6 months (range 1-14) and 36 days (range 20-55). 32/36 90% of patients had csPCa. Per-patient analysis showed a sensitivity, specificity, positive predictive value and negative predictive value of 94%, 25%, 91% and 33%, respectively. Per-segment analysis performed on 325 validated segments with the standard and the delayed acquisition resulted in a sensitivity, specificity, positive predictive value and negative predictive value of 66% vs. 67%, 84% vs. 91%, 72% vs.84% and 79% vs. 81%, respectively (p<0.01). The median SUVmax of the prostate on the standard vs delayed acquisition were 7.6 and 9.0, respectively. SUVmax was associated with presence of ISUP>2 (p=0.02).
n=100
Frequency (%)
Median SUVmax (IQR)
Positive PSMA-PET (majority rule)
85/100 (85)
Positive prostate (T)
extracapsular
seminal vesicles
85/100 (85)
3/100 (3)
26/100 (26)
7.4 (5.1-12.1)
Positive pelvic lymph nodes (N)
17/100 (17)
9.1 (4.0-17.1)
Distant metastases (M)
distant lymph nodes
bone
visceral
9/100 (9)
3/100 (3)
7/100 (7)
1/100 (lung) (1)
5.7 (4.8-30.4)
SUVs of the prostate
SUVmax
SUVmax_delayed acquisition
7.6 (4.0-13.4)
9.0 (5.9-17.6)
Conclusions: Our results suggest that PSMA PET/CT has the potential for localization of recurrent prostate cancer after focal therapy and high specificity for biopsy guidance. Adding delayed PET acquisition improved lesion detection in the segment-based analysis. Further investigation by prospective studies within larger population will be helpful for better interpretation PSMA PET criteria on patients after focal therapy.
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