Detection level and pattern of positive lesions using PSMA PET/CT for staging prior to radiation therapy

To determine the potential role of (68)Ga-PSMA positron emission tomography/computed tomography (PET/CT) in radiotherapy (RT) planning for prostate cancer (PCa).

One hundred twenty-nine patients (pts) with (68)Ga-PSMA PET/CT were retrospectively analysed. Potentially influencing factors (androgen deprivation therapy, amount of (68)Ga-PSMA-HBED-CC, PSA doubling time ≤/> 10 months, PSA before PET/CT, T-/N-category and Gleason score) were evaluated by logistic regression analysis. The detection rate of PSMA PET/CT was compared to contrast enhanced CT and its impact on RT management analysed.

One hundred twenty-nine patients (pts) (20 at initial diagnosis, 49 with PSA relapse and 60 with PSA persistence after radical prostatectomy) received PSMA PET/CT prior to RT. The majority of pts. (71.3%) had PET-positive findings (55.1% of pts. with PSA recurrence, 75% of pts. with PSA persistence and 100% of newly diagnosed pts). Median PSA before PET/CT in pts. with pathological findings (n = 92) was 1.90 ng/ml and without (n = 37) 0.30 ng/ml. PSA level at time of PET/CT was the only factor associated with PET-positivity. In pts. with a PSA ≤ 0.2 ng/ml, the detection rate of any lesion was 33.3%, with a PSA of 0.21-0.5 ng/ml 41.2% and with a PSA of 0.51-1.0 ng/ml 69.2%, respectively. Regarding the anatomic distribution of lesions, 42.2% and 14.7% of pts. with relapse or persistence had pelvic lymph node and distant metastases. In pts. at initial diagnosis the detection rate of pelvic lymph nodes and distant metastases was 20% and 10%. (68)Ga-PSMA PET/CT had a high detection rate of PCa recurrence outside the prostatic fossa in pts. being considered for salvage RT (22.4% PET-positive pelvic lymph nodes and 4.1% distant metastases). Compared to CT, PSMA PET/CT had a significantly higher sensitivity in diagnosing rates of local recurrence/primary tumour (10.1% vs. 38%), lymph nodes (15.5% vs. 38.8%) and distant metastases (5.4% vs. 14.0%). This resulted in a modification of RT treatment in 56.6% of pts.

The detection of PCa is strongly associated with PSA level at time of (68)Ga-PSMA PET/CT. PSMA PET/CT differentiates between local, regional and distant metastatic disease with implications for disease management. PSMA PET/CT allows for tumour detection in post-prostatectomy pts. with PSA ≤ 0.5 ng/ml considered for salvage RT.

Radiation oncology (London, England). 2017 Nov 10*** epublish ***

Nina-Sophie Schmidt-Hegemann, Wolfgang Peter Fendler, Alexander Buchner, Christian Stief, Paul Rogowski, Maximilian Niyazi, Chukwuka Eze, Minglun Li, Peter Bartenstein, Claus Belka, Ute Ganswindt

Department of Radiation Oncology, University Hospital, LMU Munich, Munich, Germany., Department of Nuclear Medicine, University Hospital, LMU Munich, Munich, Germany., Department of Urology, University Hospital, LMU Munich, Munich, Germany., Department of Radiation Oncology, University Hospital, LMU Munich, Munich, Germany. .