Ga-PSMA-PET imaging showed a high clinical impact on staging and RT management in patients with biochemically recurrent PC, even at low serum PSA levels. With 43% changes in staging and 59% in radiotherapy planning Ga-PSMA-PET could lead to an indispensable tool in guiding radiation treatment in recurrent PC.

BackgroundProstate cancer (PC) is one of the most commonly treated cancer entities with radiation therapy (RT). Risk group-adapted treatment and avoidance of unnecessary toxicities relies primarily on accurate tumor staging. Thus, the introduction of prostate-specific membrane antigen (PSMA) in diagnosis and treatment of PC is a highly interesting development in radiation oncology of urologic tumors. The present work is to evaluate the integration of 68Ga-PSMA-PET imaging into standard radiation planning of primary definitive treatment of PC and to determine the impact of PSMA imaging on tumor staging.MethodsThe data of 15 patients treated for PC between August 2013 and April 2015 were evaluated. Treatment planning included 68Ga-PSMA-PET imaging. We analyzed whether the use of PSMA-imaging led to a change of the TNM stage and if it influenced the RT treatment approach or the target volume, due to changes in the gross tumor volume (GTV) or clinical target volume (CTV), in the final treatment plan.ResultsIn 53.3 % of the analyzed patients a change occurred in the TNM stage based on 68Ga-PSMA-PET examination. The RT concept changed in 33.3 % of all patients, leading to relevant changes in the planning target volume. Among these, an additional irradiation of the pelvic lymph drainage due to tracer uptake in lymph nodes was performed in 25 %. Furthermore, boost volumes of PET-positive lymph nodes were added in 80 % of these cases. A down staging due to the 68Ga-PSMA-PET examination occurred in 13.3 % of all cases.ConclusionsThe integration of 68Ga-PSMA-PET-imaging into the RT treatment planning process can be useful for detailed target volume planning. The performance of a 68Ga-PSMA-PET frequently leads to changes in the TNM stage, altering the RT treatment regimen and the target volume. A prospective trial is underway to evaluate the impact of 68Ga-PSMA-PET based treatment planning on outcome.

The aim of this retrospective study was to evaluate the detection rate of Glu-NH-CO-NH-Lys-(Ahx)-[ 68 Ga(HBED-CC)] ( 68 Ga-PSMA ligand; PSMA is prostate-specific membrane antigen) PET/CT in patients with biochemical recurrent prostate cancer defined by Phoenix criteria after external-beam radiotherapy or brachytherapy as primary treatment. Methods: One hundred eighteen patients with a median prostate-specific antigen (PSA) of 6.4 ng/mL (range, 2.2-158.4 ng/mL; interquartile range, 4.2-10.2 ng/mL) were finally eligible for this retrospective analysis. Seventy-seven and 41 patients had been treated by external-beam radiotherapy or brachytherapy, respectively. Of the 118 patients, 45 were receiving androgen-deprivation therapy (ADT) within at least 6 mo before the PET/CT. The detection rates were stratified by PSA. The influence of primary Gleason score and ADT was assessed. Relationships between SUV and clinical as well as pathologic features in patients with positive findings were analyzed using univariate and multivariable linear regression models. Results: One hundred seven of 118 patients (90.7%) showed pathologic findings indicative for tumor recurrence in 68 Ga-PSMA ligand PET/CT. The detection rates were 81.8% (36/44), 95.3% (41/43), and 96.8% (30/31) for PSA of 2 to ,5, 5 to ,10, and $10 ng/mL, respectively (P 5 0.0377). 68 Ga-PSMA ligand PET/CT indicated local recurrence in 68 of 107 patients (63.5%), distant lesions in 64 of 107 patients (59.8%), and local recurrence as well as distant lesions in 25 of 107 patients (23.4%). The detection rate was significantly higher in patients with ADT (97.7%) versus without ADT (86.3%, P 5 0.0381), but independent from primary Gleason score $ 8 (92.0%) versus # 7 (90.2%, P 5 0.6346). SUV max and SUV mean were significantly associated with PSA and ADT (P 5 0.018 and 0.004 for SUV max , respectively; P 5 0.025 and 0.007 for SUV mean , respectively). Conclusion: 68 Ga-PSMA ligand PET/CT demonstrates high detection rates in patients with biochemical recurrence of prostate cancer after primary radiation therapy. The detection rate was positively associated to increasing PSA as well as concomitant ADT. 68 Ga-PSMA ligand PET/CT enables discrimination of local versus metastatic disease and thus might have a crucial impact on further clinical management. A major limitation of this study is the lack of histopathologic proof in most patients.