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

Abstract

<b>BACKGROUND</b>. 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. <b>OBJECTIVE</b>. The purpose of this study was to assess the association between bone marrow and spleen uptake and the interval between pegfilgrastim administration and FDG PET/CT. <b>METHODS</b>. This retrospective study included 70 oncology patients (mean age, 64 ± 12 [SD] years; 48 men, 22 women) receiving 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 the SUV_mean 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). <b>RESULTS</b>. Percentage change in SUV_mean between reference and study scans significantly increased (<i>p</i> < .05) as the interval increased for five sites (i.e., for patients with interval of 7-13 vs 29-35 days, mean percentage change was 32.3% ± 18.2% vs 11.5% ± 17.3% for cervical vertebra, 42.2% ± 18.3% vs 21.3% ± 14.2% for thoracic vertebra, 47.2% ± 19.8% vs 19.1% ± 13.9% for lumbar vertebra, 51.1% ± 25.8% vs 12.7% ± 11.3% for pelvis, and 53.0% ± 25.6% vs 4.4% ± 14.1% for lower extremity); percentage change was not associated with the interval for upper extremity or spleen (<i>p</i> > .05). Visual uptake scores of 4, 3, 2, and 1 were observed in days 7-21, 12-22, 12-28, and 14-35, respectively. Percentage of patients with a score of 3 or 4 was 94.4% for days 7-13, 58.1% for days 14-21, 6.7% for days 22-28, and 0% for days 29-35. A total of 71.4% of patients had a score of 3 or 4 on day 7-21, whereas 4.8% had a score of 3 and 0% had a score of 4 on days 22-35. <b>CONCLUSION</b>. A 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. <b>CLINICAL IMPACT</b>. We recommend a preferred interval of at least 3 weeks after pegfilgrastim administration before PET/CT.