Prospective inter- and intra-tracer repeatability analysis of radiomics features in [(68)Ga]Ga-PSMA-11 and [(18)F]F-PSMA-1007 PET scans in metastatic prostate cancer

OBJECTIVE: This study aimed to quantify both the intra- and intertracer repeatability of lesion-level radiomics features in [(68)Ga]Ga-prostate-specific membrane antigen (PSMA)-11 and [(18)F]F-PSMA-1007 positron emission tomography (PET) scans. METHODS: Eighteen patients with metastatic prostate cancer (mPCa) were prospectively recruited for the study and randomised to one of three test–retest groups: (i) intratracer [(68)Ga]Ga-PSMA-11 PET, (ii) intratracer [(18)F]F-PSMA-1007 PET or (iii) intertracer between [(68)Ga]Ga-PSMA-11 and [(18)F]F-PSMA-1007 PET. Four conventional PET metrics (standardised uptake value (SUV)(max), SUV(mean), SUV(total) and volume) and 107 radiomics features were extracted from 75 lesions and assessed using the repeatability coefficient (RC) and the ICC. Radiomic feature repeatability was also quantified after the application of 16 filters to the PET image. RESULTS: Test–retest scans were taken a median of 5 days apart (range: 2–7 days). SUV(mean) demonstrated the lowest RC limits of the conventional features, with RCs of 7.9%, 14.2% and 24.7% for the [(68)Ga]Ga-PSMA-11 PET, [(18)F]F-PSMA-1007 PET, and intertracer groups, respectively. 69%, 66% and 9% of all radiomics features had good or excellent ICC values (ICC ≥ 0.75) for the same groups. Feature repeatability therefore diminished considerably for the intertracer group relative to intratracer groups. CONCLUSION: In this study, robust biomarkers for each tracer group that can be used in subsequent clinical studies were identified. Overall, the repeatability of conventional and radiomic features were found to be substantially lower for the intertracer group relative to both intratracer groups, suggesting that assessing patient response quantitatively should be done using the same radiotracer where possible. ADVANCES IN KNOWLEDGE: Intertracer biomarker repeatability limits are significantly larger than intratracer limits.