Baskent University Faculty of Medicine Adana, Yuregir
H. C. Onal1,2, O. C. Guler1, N. Torun3, A. Elmali Dogan4, P. Sutera5, M. Deek6, M. Reyhan3, M. N. Yavuz4, and P. T. Tran7; 1Department of Radiation Oncology, Baskent University Faculty of Medicine, Ankara, Turkey, 2Baskent University Faculty of Medicine, Adana Dr Turgut Noyan Research and Treatment Center, Department of Radiation Oncology, Adana, Turkey, 3Baskent University Faculty of Medicine, Adana Dr Turgut Noyan Research and Treatment Center, Department of Nuclear Medicine, Adana, Turkey, 4Baskent University Faculty of Medicine, Department of Radiation Oncology, Ankara, Turkey, 5Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins Medicine, Baltimore, MD, 6Department of Radiation Oncology, Rutgers Cancer Institute of New Jersey, New Brunswick, NJ, 7Johns Hopkins University, School of Medicine, Baltimore, MD
Purpose/Objective(s): To assess the prostate-specific membrane antigen (PSMA) change of primary tumor using Gallium-68 (68Ga)-labeled-PSMA positron emission tomography (68Ga-PSMA-PET/CT), as well as the correlation between PSMA change in the primary tumor and prostate-specific antigen (PSA) response after definitive radiotherapy (RT), either alone or in combination with androgen deprivation therapy (ADT), in patients with intermediate-risk prostate cancer (IR-PCa). Materials/
Methods: The clinical data of 71 patients with IR-PCa treated with RT alone (50.7%) or RT and ADT (49.3%) were retrospectively analyzed. The differences between pre- and post-treatment primary tumor PSMA expression and serum PSA values measured 4 months after the completion of treatment were compared between the treatment arms. Results: The median duration between pre- and post-treatment 68Ga-PSMA-PET/CT for the entire patient population was 6.9 months (range, 5.6–8.4 months), and it was similar in both treatment arms. A decrease in primary tumor SUV was seen in 66 patients (93.0%), with a median value of 61.2%, which is significantly lower in patients undergoing RT alone than those undergoing RT and ADT (45.1±30.6% vs. 59.1±24.7%; p = 0.004). The complete metabolic response rate was significantly higher in patients undergoing RT and ADT than those treated with RT alone (40% vs. 0%; p < 0.001). The PSA response, observed at a median of 4.1 months (range, 3.8–4.8 months) after RT, was noted in 70 patients (98.6%). The median decrease for the entire cohort was 82.5% (range, 4.0–100%). There was a significant difference in pre- and post-treatment PSA values for patients treated with RT alone (10.5±4.8 ng/mL vs. 4.1±2.6 ng/mL; p < 0.001) and patients treated with RT and ADT (12.1±4.7 ng/mL vs. 1.0±1.5 ng/mL; p < 0.001). Although moderate and positive correlation between pre-treatment SUV and post-treatment SUV was observed (Pearson correlation coefficient [r] = 0.40; p = 0.017), there was no significant correlation between SUV change and PSA change in patients treated with RT and ADT (r = 0.05; p = 0.79) or RT alone (r = 0.07; p = 0.71) . For patients treated with RT and ADT, post-treatment SUV was significantly lower and SUV change was significantly higher in patients with PSA nadir than in those without. Post-treatment SUV was significantly lower (3.1±1.3 vs. 8.3±7.8; p < 0.001) and SUV change was significantly higher (62.1±21.8% vs. 47.3±34.8%; p = 0.04) in patients with PSA nadir than in those without. Conclusion: We showed that RT, with or without ADT, significantly reduced primary tumor SUV and serum PSA levels in patients with IR-PCa. Our findings indicate that early treatment response using 68Ga-PSMA-PET/CT is not feasible for patients treated with RT alone and may only be useful in distinguishing patients with and without a PSA nadir for those who received both RT and ADT.
