Abstract
1705
Objectives: We evaluated normal spleen and liver uptake of 68Ga‐ DOTA‐DPhe1, Tyr3‐octreotate (DOTATATE) using positron emission tomography (PET) / computed tomography (CT) to assess correlations with patient age, gender, and body mass index (BMI). We hypothesized splenic tracer uptake (mainly in SSTR2 positive lymphocytes) would decline with age due to known age-related declines in splenic volumes and the reduced immunological competence in older patients.
Methods: Patients who underwent DOTATATE PET/CT imaging for the evaluation of suspected neuroendocrine tumors were included in this IRB-approved retrospective study. Using MIM 6.9.3 (MIM Software Inc., Cleveland, US), whole spleen and liver regions of interest (ROI) were manually created. Final ROIs were formed by then removing all voxels within the manual ROI which were less than 25% of the maximum standardized uptake value (SUVMAX). Liver and spleen total lesion receptor (radiopharmaceutical) content (TLRC) and SUVMAX were extracted from each ROI. Extracted PET metrics were then correlated with patient age, gender, and BMI. Data are reported using correlation coefficients and median (IQR). Data analyses were performed using SPSS.
Results: Seventy-two patients (35M/37W; mean age 51.1±23.4 years) underwent DOTATATE PET/CT imaging and were eligible for liver and spleen analyses. DOTATATE TLRC in the spleen showed a modest but borderline significant decline with increasing age (p = 0.054, r2 = 0.05; Fig 1A). Females showed spleen TLRC (Total Lesion Receptor Content) of 4123.8 (1012.5-14803.74) versus 6300.36 (1079.16-11681.28) for males (p = 0.24; Fig 1B). Median (IQR) TLRC was 3769.85 (1012.5-14803.74), 5540.4 (1255.5-9322.02), and 5599.9 (1761.54-11792.96) for normal, overweight, and obese patients, respectively (p = 0.19; Fig 1C). Splenic DOTATATE SUVMAX showed an insignificant change with increasing age (p = 0.34, r2 = 0.01; Fig 2A). Females showed splenic SUVMAX of 27.8 (16.7-50.5) versus 29.4 (13.2-47.5) for males (p = 0.19; Fig 2B). Median (IQR) TLRC was 24.2 (14.2-47.5), 29.3 (13.2-50.5), and 31.5 (16.7-42.1) for normal, overweight, and obese patients, respectively (p = 0.150; Fig 2C). Thus, declines in splenic TLRC are likely mainly related to age related declines in splenic volume but not receptor density as reflected by SUV. DOTATATE TLRC in the liver tended to showed a slight decline with increasing age (p = 0.095; r2 = 0.06; Fig 3A). Females showed a median (IQR) TLRC of 9707.62 (5326.95-14673.04) versus 11069.13 (5812.58-15751.3) for males (p = 0.04; Fig 3B). Median (IQR) TLRC was 8519.94 (5326.95-13190.59), 10096.61 (5812.58-14488.01), and 11066.93 (8578.80-15751.30) for normal, overweight, and obese patients, respectively (p = 0.005; Fig 3C). Liver DOTATATE SUVMAX was stable with age (r2 = 0.00; p = 0.880; Fig 4A). Females showed a liver SUVMAX of 11.9 (8.1-47.7) versus 12.4 (8.6-26.1) for males (p = 0.00; Fig 4B). Median (IQR) TLRC was 11.9 (8.7-13.9), 11.5 (8.1-15.3), and 12.4 (9.6-47.7) for normal, overweight, and obese patients, respectively (p = 0.170; Fig 4C).
Conclusions: These results indicate a small but significant decline in splenic DOTATATE TLRC with increasing age, likely mainly related to declines in splenic volume. Liver and spleen SUVMAX and TLRC appear to increase with increasing BMI, albeit insignificantly in this relatively small cohort. Our findings may have potential implications for the interpretation of 68Ga‐DOTATATE uptake in the spleen and liver in the normal population and hold additional potential as a tool for non-invasively phenotyping SSTR2-positive spleen cells important in immune function. $$graphic_09DEEB41-7FA3-44FD-B8B8-EA898AE4DD75$$ $$graphic_1815D8C9-4E8F-4B37-9D0E-F71E8C2EB274$$
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