Optimal acquisition time of [68Ga]Ga-PentixaFor PET/CT for initial staging of multiple myeloma: an ancillary study to the PentiMyelo protocol

[68Ga]Ga-PentixaFor, a CXCR4-targeted PET tracer, has shown potential in multiple myeloma. However, [68Ga]Ga-PentixaFor-PET/CT acquisition protocols lack standardization. This is a prospective ancillary study to the PentiMyelo trial aimed to determine the optimal acquisition time for [68Ga]Ga-PentixaFor-PET. Twenty multiple myeloma patients underwent [68Ga]Ga-PentixaFor-PET/CT at 60 min post-injection, with additional acquisitions at 30, 40, 50 min (Group 1) or 75, 85, 95 min (Group 2). Semi-quantitative metrics including SUV, tumor-to-background ratios and image noise — assessed by the coefficient of variation, were systematically analyzed. Physiological liver, spleen and mediastinal blood-pool uptakes decreased over time while image noise increased. A total of 343 lesions were detected (316 in Group 1, 27 in Group 2). Neither earlier nor later acquisition time affected the positivity of [68Ga]Ga-PentixaFor-PET, which was positive in 10 of 20 patients (5 in Group 1 and 5 in Group 2). In Group 1, tumor-to-background ratio was significantly higher at 60 min; in Group 2, tumor-to-background ratio remained stable. An acquisition time of 60 min post-injection provided optimal lesion contrast, supporting its adoption as the standard imaging time point for [68Ga]Ga-PentixaFor-PET/CT. Name of the registry: ClinicalTrials.gov. Trial registration number: NCT04561492. Date of registration: 17 September 2020. URL of trial registry record: https://clinicaltrials.gov/study/NCT04561492. This imaging sub-study is ancillary to the PentiMyelo prospective trial registered under the identifier NCT04561492.