Impact of Cold Somatostatin Analog Administration on Somatostatin Receptor Imaging: A Systematic Review

Determinants of the uptake of the uncinate process of pancreas in 68Ga-DOTATOC PET/CT: a retrospective study

PURPOSE

an increased uptake of the uncinate process of pancreas (UPP) has been described in about one-third of somatostatin receptor imaging procedures and may hinder image interpretation. The determinants of this uptake are however poorly understood. The aim of this study was to investigate the impact of cold somatostatin analogues (cSA) on UPP 68Ga-DOTATOC uptake. Age and diabetic status were also studied.

METHODS

all adult patients who performed a 68Ga-DOTATOC PET/CT in our center between May 2021 and April 2023 were retrospectively screened. For each one, UPP uptake was visually assessed and measured using SUVmax. Clinical data including cSA medication, age and diabetic status were collected. Univariate and multivariate analyses were conducted using logistic regression. SUVmax comparisons were conducted using a Mann-Whitney Wilcoxon test.

RESULTS

82 patients were included. UPP uptake was significantly lower in patients treated with cSA (OR 0.27, p = 0.015 in multivariate analysis), with a lower SUVmax (4.97 vs. 8.81, p = 0.001). No significant result was found regarding diabetic status or age.

CONCLUSION

cold somatostatin analog treatment decreased the physiological UPP uptake in 68Ga-DOTATOC PET/CT. This effect could be used to reduce interpretation errors in this location.

Peptide Receptor Radionuclide Therapy Performed Shortly After Administration of Long-Acting Octreotide

ABSTRACT

We present a case of a 68-year-old man with metastatic small bowel neuroendocrine tumor who underwent 4 cycles of peptide receptor radionuclide therapy with 177 Lu-DOTATATE. For his first 3 cycles, therapy was performed approximately 4 weeks after his last dose of octreotide LAR. Because of miscommunication in scheduling, his fourth cycle was performed only 48 hours after his last full dose of octreotide LAR. Despite this, we found that the tumoral uptake was not reduced at all, which may add to the increasing evidence on the nonnecessity of stopping somatostatin analogs before peptide receptor radionuclide therapy.

Quantitative uptake in 99m Tc-EDDA/HYNIC-TOC somatostatin receptor imaging - the effect of long-acting release somatostatin analogue therapy

PURPOSE

Withdrawal of long-acting release somatostatin analogue (LAR-SSA) treatment before somatostatin receptor imaging is based on empirical reasoning that it may block uptake at receptor sites. This study aims to quantify differences in uptake of 99m Tc-EDDA/HYNIC-TOC between patients receiving LAR-SSA and those who were not.

METHODS

Quantification of 177 patients (55 on LAR-SSA) imaged with 99m Tc-EDDA/HYNIC-TOC was performed, with analysis of pathological tissue and organs with physiological uptake using thresholded volumes of interest. Standardised uptake values (SUVs) and tumour/background (T/B) ratios were calculated and compared between the two patient groups.

RESULTS

SUVs were significantly lower for physiological organ uptake for patients on LAR-SSA (e.g. spleen: SUV max 13.3 ± 5.9 versus 33.9 ± 9.0, P  < 0.001); there was no significant difference for sites of pathological uptake (e.g. nodal metastases: SUV max 19.2 ± 13.0 versus 17.4 ± 11.5, P  = 0.552) apart from bone metastases (SUV max 14.1 ± 13.5 versus 7.7 ± 8.0, P  = 0.017) where it was significantly higher.

CONCLUSION

LAR-SSA has an effect only on physiological organ uptake of 99m Tc-EDDA/HYNIC-TOC, reducing uptake. It has no significant effect on pathological uptake for most sites of primary and metastatic disease. This should be taken into account if making quantitative measurements, calculating T/B ratios or assigning Krenning Scores. There is the potential for improved dosimetric results in Peptide Receptor Radionuclide Therapy by maintaining patients on LAR-SSA.

The Influence of Long-Acting Somatostatin Analogs on 68 Ga-DOTATATE Uptake in Patients With Neuroendocrine Tumors

PURPOSE

A high SUV max tumor-to-liver ratio (TLR) of 68 Ga-DOTATATE can be used to select patients with neuroendocrine tumors (NETs) for peptide receptor radionuclide therapy (PRRT). In addition, an SUV max TLR ≥ 8.1 is associated with increased progression-free survival in NET patients treated with somatostatin analogs (SSAs). To avoid a theoretical interaction, several guidelines recommend performing PET/CT just before the monthly administration of long-acting SSAs. We aimed to investigate the effect of SSA on the SUV max of 68 Ga-DOTATATE in patients with NET and to identify independent predictors for high SUV max TLR.

PATIENTS AND METHODS

For this retrospective study, 192 68 Ga-DOTATATE PET/CT scans of 165 patients without (n = 115) and with (n = 77) SSA (octreotide or lanreotide) in the 3 months before PET/CT were collected and reviewed. The effect of SSA on SUV max values was analyzed by a maximum likelihood mixed model.

RESULTS

Patients with SSA had a significantly higher median SUV max TLR than patients without SSA (4.7 [IQR], 3.1-7.7) versus 3.2 [IQR, 2.0-5.4]; P < 0.001). Multivariable logistic regression analysis showed that SSA use was an independent predictor for SUV max TLR ≥ 8.1 (odds ratio, 2.91; 95% confidence interval, 1.26-6.72; P = 0.012).

CONCLUSIONS

Our data suggest that higher SSA concentrations do not have a negative effect on 68 Ga-DOTATATE uptake in tumor lesions. In addition, we found that only SSA use was associated with SUV max TLR ≥ 8.1. Our results are consistent with previously conducted studies and in line with the recently published guideline that suggests that the relatively recent use of SSA does not necessitate any delay in 68 Ga-DOTATATE PET/CT imaging.