E3283. 177Lu-PSMA SPECT Quantitation in Patients with Metastatic Castrate Resistant Prostate Cancer
Authors
Esmaeil Gharepapagh;
Clinical Research Development Unit of Tabriz Valiasr Hospital, Tabriz University of Medical Sciences; Department of Nuclear Medicine, Medical School, Tabriz University of Medical Sciences
Sahar Rezaei;
Clinical Research Development Unit of Tabriz Valiasr Hospital, Tabriz University of Medical Sciences; Department of Nuclear Medicine, Medical School, Tabriz University of Medical Sciences
Objective:
A promising therapeutic option is [177Lu]-PSMA-617 (Lu-PSMA) therapy for metastatic castrate-resistant prostate cancer (mCRPC). A positive response to treatment after two therapy cycles may be associated with higher treatment efficacy and longer overall survival. Thus, this study aimed to determine if early tumor volume reduction is a favorable prognosticator for increased overall survival.
Materials and Methods:
A total of 40 men with progressive mCRPC previously treated with androgen signaling inhibition and chemotherapy were treated with Lu-PSMA at doses of 5.8 - 6 GBq. Lu-PSMA SPECT imaging was performed 24 hours after treatment. A quantitative Lu- PSMA SPECT analysis was performed at cycle 1 (baseline) and cycle 2 (week 6). Each manually identified lesion was quantitatively reviewed, physiologic activity removed, and whole-body quantitation was used to determine total tumor volume (TTV). PSA progression-free and overall survival were assessed based on clinical and biochemical results.
Results:
Between baseline and week 6, SPECT-total tumor volume (SPECT-TTV) decreased by 65%. PSA progression-free and overall survival were not significantly associated with SPECT-TTV (dose 1). PSA progression-free survival was significantly shorter between baseline and week 6 when SPECT-TTV was increased, but not overall survival. When both PSA and SPECT-TTV were increased, PSA progression-free was considerably different from when both were reduced.
Conclusion:
PSMA SPECT-total tumor volume reduction can be used as an imaging response biomarker to identify when to discontinue or intensify Lu-PSMA therapy, as it was a positive predictor of PSA progression-free survival and overall survival.
