68Ga-PSMA-11 PET/CT-derived metabolic parameters for determination of whole-body tumor burden and treatment response in prostate cancer
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We aimed at evaluating the role of 68Ga-PSMA-11 PET/CT-derived metabolic parameters for assessment of whole-body tumor burden and its capability to determine therapeutic response in patients with prostate cancer.
A total of 142 patients with biochemical recurrence of prostate cancer underwent PET/CT with [68Ga]Ga-PSMA-HBED-CC (68Ga-PSMA-11). Quantitative assessment of all 641 68Ga-PSMA-11-positive lesions in the field of view was performed to calculate PSMA-derived parameters, including whole-body PSMA tumor volume (PSMA-TV) and whole-body total lesion PSMA (TL-PSMA), as well as the established SUVmax and SUVmean values. All PET-derived parameters were tested for correlation with serum PSA levels and for association with Gleason scores.
In 23 patients who underwent 68Ga-PSMA-11 PET/CT before and after therapy with either external beam radiation, androgen deprivation, or docetaxel chemotherapy, SUVmax and TL-PSMA were compared to radiographic response assessment of CT images based on RECIST 1.1 criteria and to biochemical response determined by changes of serum PSA levels.
PSMA-TV and TL-PSMA demonstrated a significant correlation with serum PSA levels (P < 0.0001) and TL-PSMA was significantly different for different Gleason scores. The agreement rate between TL-PSMA derived from PET and biochemical response was 87% (95% confidence interval, 0.66–0.97; Cohen’s κ = 0.78; P < 0.01) and, thus, higher than for SUVmax, which was 74% (95% CI, 0.52–0.90; κ = 0.55; P < 0.01). Furthermore, agreement with PSA was higher for TL-PSMA and SUVmax than for CT-based response evaluation. Discordant findings between PET and CT were most likely due to limitations of CT and RECIST in rating small lymph nodes as metastases, as well as bone involvement, which was sometimes not detectable in CT.
68Ga-PSMA-11 PET/CT-derived metabolic tumor parameters showed promising results for evaluation of treatment response. Especially, TL-PSMA demonstrated higher agreement rates with biochemical response compared to SUVmax. Larger, ideally prospective trials are needed to help to reveal the full potential of metabolic parameters derived from PET imaging with 68Ga-PSMA-11.
Keywords68Ga-PSMA-11 PET/CT Prostate cancer Metabolic tumor parameters Treatment response Whole-body tumor burden
Compliance with ethical standards
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.
Informed consent was obtained from all individual participants included in the study.
Conflicts of interest
Schmidkonz C, Cordes M, Beck M, Goetz Th I, Schmidt D, Prante O, Kuwert T, Ritt P: The Clinic of Nuclear Medicine in Erlangen has research cooperation with Siemens in the field of SPECT/CT, but not related to the data contained in this manuscript.
Kuwert T: has received honoraria for lectures on behalf of Siemens Molecular Imaging.
Goebell P: has received honoraria for lectures and participation in expert meetings from Pfizer, Janssen-Cilag, Novartis, GSK, BMS, and Bayer.
Wullich B: has received honoraria for lectures and participation in expert meetings from Janssen-Cilag and Astellas.
Uder M: has received honoraria for lectures and grants from Siemens, Bayer, Bracco, and Medtronic.
Bäuerle T: has received Honoria for lectures and grants from Bayer, Bracco, and Boeringer Ingelheim.
Beck M: has received honoraria for lectures from Bayer.
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