Association of Time Since Administration of Pegylated G-CSF (Pegfilgrastim) and Bone Marrow Uptake on FDG PET/CT: Determination of a Minimum Interval.

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Abstract

Background: Pegfilgrastim administration after chemotherapy increases bone marrow and spleen FDG uptake. Consensus is lacking regarding the optimal interval between pegfilgrastim administration and FDG PET/CT. Objective: To assess the association between bone marrow and spleen uptake and the interval between pegfilgrastim administration and FDG PET/CT. Methods: This retrospective study included 70 oncology patients (mean age, 64±12 years; 48 male, 22 female) on chemotherapy who underwent FDG PET/CT (study scan) within 35 days after pegfilgrastim administration and who underwent additional FDG PET/CT at least 4 months before pegfilgrastim initiation or at least 3 months after last pegfilgrastim administration (reference scan). A nuclear medicine physician recorded SUVmean for normal osseous structures and spleen and assessed bone marrow uptake using a 4-point visual scale (1=no abnormal uptake, 2=clinically insignificant uptake, 3=clinically significant uptake possibly interfering with interpretation, 4=clinically significant uptake expected to interfere with interpretation). Results: Percentage change in SUVmean between reference and study scans increased (p<.05) as the interval increased for five sites (i.e., percentage change for patients with interval of 7-13 days versus 29-35 days of 32.3±18.2 versus 11.5±17.3 for cervical vertebrae, 42.2±18.3 versus 21.3±14.2 for thoracic vertebrae, 47.2±19.8 versus 19.1±13.9 for lumbar vertebrae, 51.1±25.8 versus 12.7±11.3 for pelvis, and 53.0±25.6 versus 4.4±14.1 for lower extremity); percentage change was not associated with the interval for upper extremity or spleen (p>.05). Visual uptake score of 4 was observed in days 7-21, score of 3 in days 12-22, score of 2 in days 12-28, and score of 1 in days 14-35. Percentage of patients with score 3 or 4 was 94.4% for days 7-13, 58.1% for 14-21 days, 4.8% for 22-28 days, and 0% for 29-35 days. A total of 71.4% of patients showed score 3 or 4 on day 7-21, whereas 3.2% showed score of 3 and 0.0% showed score of 4 on day 22-35. Conclusion: Visual uptake score of 3 or 4 was consistently observed throughout an approximately 3 week interval following pegfilgrastim administration, without any such case beyond 22 days. Clinical Impact: We recommend a preferred interval of at least 3 weeks after pegfilgrastim administration prior to PET/CT.

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