*Corresponding author:
Lara Schwarte, Klinik und Poliklinik für Nuklearmedizin, Sigmund-Freud-Str. 25, 53127 Bonn, GermanyReceived: November 26, 2018; Published: December 07, 2018
DOI: 10.26717/BJSTR.2018.11.002161
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Purpose: Tumor heterogeneity in PET/CT assessed by textural parameters is gaining importance as prospective and predictive feature for multiple clinical applications. Especially in theranostics, PET and SPECT images are often performed in the same patient. Therefore, the aim of this study was to compare, if tumor heterogeneity assessed in PET/CT and SPECT/CT imaging is correlating to each other and results found for tumor heterogeneity assessed in PET may be translated to SPECT imaging. This was evaluated in phantom and patient data.
Subjects and Methods: A self-built heterogeneity phantom as well as 37 patients with metastasized prostate cancer were analyzed. All patients underwent a peptide receptor radionuclide therapy (PRRT, one to four cycles) and received a 68Ga-PSMA PET/CT before and 177Lu-PSMA SPECT/CT directly after each therapy cycle. Both PET/CT and SPECT/CT images were processed with Interview™ Fusion software (Mediso Medical Imaging Systems). The biggest lesions of each patient were selected and manually delineated in both nuclear medicine images. Consequently 36 textural features, including deviation, entropy and different emphases were calculated. In addition, conventional parameters as mean and maximum SUV, and tumor volume were tested as well. Phantom studies were compared directly, and patient data were compared using Bland-Altman Plots.
Results: Overall, 188 metastases in 37 patients were analyzed. In Bland-Altman Plots it was shown that for the majority of the 40 parameters there is no direct comparability between PET/CT and SPECT/CT values. Using the 95% confidence interval, the best parameters could be identified. Long zone low grey level emphasis had a high accordance, 94.7% of the data were contained in 95% confidence interval. For the short zone low grey level emphasis, it was 32.8%, 32.3% for the volume, 34.9% for TLRD, 23.8% for maximum and 21.7% for the mean SUV. Variables such as entropy which are frequently used in tumor heterogeneity have low accordance values. Only 12.2% of the entropy data are contained in the 95% confidence interval. Intensity variation and zone length non-uniformity only have results of 4.2%. Different results were found for the phantom, in which differences in heterogeneity parameters were down to 0.8 % for the best parameter (Zone percentage), also low values were found for Contrast (1.4 %) and Entropy (3.5 %).
Conclusion: This study shows, that in contrast to data obtained by phantom data, in real patients’ tumor heterogeneity in PET/CT and SPECT/CT seems not to be correlating. Therefore, further studies looking in to the clinical value of tumor heterogeneity obtained in SPECT/CT images must be performed in the future to show the values of this modality.
Keywords : Prostate cancer; PSMA-PET/CT; PSMA-SPECT/CT; PRRT; Textural parameters
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