Uptake pattern of [68Ga]Ga-DOTA-NOC in tissues: implications for inflammatory diseases

[68Ga]Ga-DOTA-NOC binds to somatostatin receptor (SSTR) subtypes 2 and 5, also expressed on lymphocytes and macrophages, but no information is available about uptake in tissues that might be affected by a chronic inflammatory process. Our aim was to obtain normal reference values for: [68Ga]Ga-DOTA-NOC uptake in tissues prone to chronic inflammation.

Retrospective study in 81 patients who performed the scan for a suspicion of neuroendocrine tumor (NET). We analyzed major joints, salivary glands, thyroid, aortic wall from images acquired after injection of 173.9±1 Mbq of: [68Ga]Ga-DOTA-NOC. We calculated the SUVmax and SUVtarget/SUVgluteus ratio or SUVtarget/SUVaorta ratio. Data are reported as mean±2 or ±3 standard deviations (SD).

SUVmax values appeared more reliable than other ratios. In thyroid we found a mean SUVmax of 1.36±0.45, with no values >3SD; in parotid glands 0.98±0.40, with 2 values >3SD; in submandibular glands 0.99±0.37, with 2 values >3SD; in aortic arch 1.71±0.50, with 1 value >3SD; in thoracic aorta 2.03±0.52, with 1 value >3SD; in abdominal aorta 2.19±0.49, with no value >3SD; in shoulders 0.92±0.31 and in hips 0.87±0.34, with 2 and 4 values >3SD, respectively. These 12 values with SUVmax >3SD, belong to 5 patients, 3 of which had signs of xerostomia and/or arthritis. A statistically significant correlation was observed between SUVmax and age in all examined tissues but in the aorta.

Tissues in which lymphocytic infiltration may occur show that SUVmax is tissue-dependent. Within tissue variability, an SUVmax greater than the mean +3SD is rarely found amongst patients without a symptomatic chronic inflammatory process but, when found, may highlight a chronic inflammatory condition.