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MP48-16 18F-DCFPYL PSMA PET IMAGING IMPROVES DETECTION OF NODAL METASTASES IN COMPARISON TO CONVENTIONAL IMAGING IN PATIENTS WITH LOCALLY ADVANCED OR OLIGOMETASTATIC PROSTATE CANCER

INTRODUCTION AND OBJECTIVE: PSMA PET allows accurate localization of tumour recurrence in patients with biochemical recurrence post-radical prostatectomy. Correlations between histopathological parameters and disease recurrence are established. We aim to qualitatively and quantitatively assess topographic concordance of histopathological factors with PET local recurrences. METHODS: Our cohort was selected from the 100 men who received a F-DCFPyL PET scan through IMPPORT trial, a prospective non-randomised study for men with a rising PSA (>0.2 ng/mL) post prostatectomy. Patients with local recurrences were included in our study. Histopathological parameters including ISUP Grade Group, location of tumour, extraprostatic extension (EPE) and positive margins were collated from prostatectomy reports. Pre-defined concordance between the location of histopathological lesions and local recurrences were classified in three dimensional planes. Individual prostate heights and tumour locations were used to define likely tumour distances from the prostatic membranous urethral junction, and correlated with the height of the local recurrence from the vesicourethral anastomosis for quantitative analysis. RESULTS: 24 patients were eligible, median age was 71 yrs, median PSA 0.37 ng/ml and median time between prostatectomy and PET was 2.6 years. 15 patients had recurrences within the vesicourethral anastomotic region and 9 within the lateral surgical margins where the seminal vesicle (SV) bed lies. 100% concordance in the left to right plane between tumour location and local recurrence was found, with 79% of these lesions concordant three dimensionally. 42% of patients had three dimensional concordance between the location of their EPE and their local recurrence, and 21% of positive surgical margins. 17 of the 24 patients had recurrent lesions within their tumour height range (Graph 1). Five of these were recurrences were reported as lateral surgical margin recurrences. CONCLUSIONS: Local recurrence is highly concordant with the position of the tumour within the prostate. Low total concordance with positive surgical margins, raises concern that a negative surgical margin may not be as protective against local recurrence as previously hypothesised.