PURPOSE

Paired imaging/therapy with radiolabeled somatostatin receptor (SSTR) antagonists is a novel approach in neuroendocrine tumors (NETs). The aim of this study was to compare tumor uptake of Ga-DOTA-JR11 and Lu-satoreotide tetraxetan (Lu-DOTA-JR11) in patients with NETs.

METHODS

As part of a prospective clinical trial, 20 patients with metastatic NETs underwent Ga-DOTA-JR11 PET/CT and serial imaging with Lu-satoreotide tetraxetan. PET/CT and SPECT/CT parameters for lesion uptake and absorbed dose of Lu-satoreotide tetraxetan in lesions were compared using linear regression analysis and Pearson correlation.

RESULTS

A total of 95 lesions were analyzed on Ga-DOTA-JR11 PET/CT and Lu-satoreotide tetraxetan SPECT/CT. SUVs and tumor-to-normal-tissue ratios on PET/CT and SPECT/CT were significantly correlated (p < 0.01), but the degree of correlation was modest with Pearson correlation coefficients ranging from 0.3 to 0.7. Variation in intrapatient lesional correlation was observed. Nevertheless, in all patients, the lesion SUVpeak uptake ratio for Lu-satoreotide tetraxetan vs. Ga-DOTA-JR11 was high; even in those with low uptake on Ga-DOTA-JR11 PET/CT (SUVpeak ≤ 10), a ratio of 8.0 ± 5.2 was noted. Correlation of SUVpeak of Ga-DOTA-JR11 with projected Lu-satoreotide tetratexan-absorbed dose (n = 42) was modest (r = 0.5, p < 0.01), while excellent correlation of SUVpeak of Lu-satoreotide tetraxetan with projected Lu-satoreotide tetraxetan-absorbed dose was noted (r = 0.9, p < 0.0001).

CONCLUSION

Our study shows that Ga-DOTA-JR11 PET can be used for patient selection and PRRT and that low tumor uptake on PET should not preclude patients from treatment with Lu-satoreotide tetraxetan. The ability to use single time-point SPECT/CT for absorbed dose calculations could facilitate dosimetry regimens, save costs, and improve patient convenience.