Pretherapeutic estimation of kidney function in patients treated with peptide receptor radionuclide therapy: can renal scintigraphy be safely omitted?

The Dependence of Renal 68Ga[Ga]-DOTATOC Uptake on Kidney Function and Its Relevance for Peptide Receptor Radionuclide Therapy with 177Lu[Lu]-DOTATOC

Background: In addition to its SSTR-specific binding in tumors and healthy tissues, DOTATOC analogues accumulate in kidney parenchyma. Renal tracer uptake might be a surrogate of kidney function or dysfunction. This study aimed to evaluate if kidney function can be estimated from ⁶⁸Ga[Ga]-DOTATOC uptake in PET/CT and its impact on the nephrotoxicity of ¹⁷⁷Lu[Lu]-DOTATOC PRRT. Methods: Two cohorts of patients (A: 128 diagnostic patients; B: 32 PRRT patients) were evaluated retrospectively. SUV values of the kidneys, physiologically SSTR-expressing organs and in background compartments were assessed. Kidney function was calculated as eGFR by CKD-EPI creatinine equation. Pearson’s correlation coefficients and treatment-induced changes of uptake and kidney function were assessed and compared. Results: Kidney function and renal DOTATOC uptake showed a significant inverse correlation (R² = 0.037; p = 0.029). Evaluated models of PET/CT measurements were not able to predict kidney function sufficiently. The uptake of other organs did not depend on eGFR. While the renal uptake increased after PRRT (p < 0.001), the kidney function did not change significantly (p = 0.382). Neither low pre-therapeutic eGFR nor high pre-therapeutic kidney uptake were risk factors of PRRT-induced deterioration in kidney function. Conclusion: The relevance of kidney function for renal ⁶⁸Ga[Ga]-DOTATOC uptake is limited. The nephrotoxicity of ¹⁷⁷Lu[Lu]-DOTATOC PRRT might be low and cannot be reliably predicted by pre-therapeutic measurements.

Salvage PRRT with 177Lu-DOTA-octreotate in extensively pretreated patients with metastatic neuroendocrine tumor (NET): dosimetry, toxicity, efficacy, and survival

Background

NETTER-1 trial demonstrated high efficacy and low toxicity of four cycles of Peptide Receptor Radionuclide Therapy (PRRT) in patients with metastasized NET. The present study evaluates the outcome of further PRRT cycles in the so called salvage setting in patients after initial response to four therapy cycles and later progression.

Methods

Thirty five patients (pat.) (25 male, 10 female, 63 ± 9 years) with progressive, metastasized NET (23 small intestinal, 5 lung, 4 CUP, 1 rectal, 1 gastric and 1 paraganglioma) were included. All patients previously received 4 PRRT cycles with ¹⁷⁷Lu-DOTATATE and showed initial response. SPECT based dosimetry was applied to determine kidney and tumor doses. Therapy response was evaluated using ⁶⁸Ga-DOTATATE PET/CT (with high dose CT), CT alone or MRI (RECIST 1.1), toxicity was defined using CTCAE 5.0 criteria. ^99mTc99-MAG3 scintigraphy was used to assess potential renal tubular damage. Progression free survival (PFS) and Overall survival (OS) analysis was performed with the Kaplan-Meier-method.

Results

The median PFS after initial PRRT was 33 months (95% CI: 30–36). The mean cumulative dose for including salvage PRRT was 44 GBq (range 33.5–47). One pat. (2.9%) showed grade 3 hematotoxicity. Kidney dosimetry revealed a mean cumulative kidney dose after a median of 6 PRRT cycles of 23.8 Gy. No grade 3 / 4 nephrotoxicity or relevant decrease in renal function was observed. Follow-up imaging was available in 32 patients after salvage therapy. Best response according to RECIST 1.1. was PR in one patient (3.1%), SD in 26 patients (81.3%) and PD in 5 patients (15.6%). PFS after salvage therapy was 6 months (95% CI: 0–16; 8 patients censored). Mean OS after initial PRRT was 105 months (95% CI: 92–119) and 51 months (95% CI: 41–61) after start of salvage therapy. Median OS was not reached within a follow-up of 71 months after initial PRRT and 25 months after start of salvage PRRT, respectively.

Conclusions

Salvage therapy with ¹⁷⁷Lu-DOTATATE is safe and effective even in patients with extensive previous multimodal therapies during disease progression and represents a feasible and valuable therapy option for progressive NET.

Electronic supplementary material

The online version of this article (10.1186/s12885-019-6000-y) contains supplementary material, which is available to authorized users.

The impact of 177Lu-octreotide therapy on 99mTc-MAG3 clearance is not predictive for late nephropathy

Peptide Receptor Radionuclide Therapy (PRRT) for the treatment of neuroendocrine tumors may lead to kidney deterioration. This study aimed to evaluate the suitability of ^99mTc-mercaptoacetyltriglycine (^99mTc­-MAG3) clearance for the early detection of PRRT-induced changes on tubular extraction (TE). TE rate (TER) was measured prior to 128 PRRT cycles (7.6±0.4 GBq ¹⁷⁷Lu-octreotate/octreotide each) in 32 patients. TER reduction during PRRT was corrected for age-related decrease and analyzed for the potential to predict loss of glomerular filtration (GF). The GF rate (GFR) as measure for renal function was derived from serum creatinine. The mean TER was 234 ± 53 ml/min/1.73 m² before PRRT (baseline) and 221 ± 45 ml/min/1.73 m² after a median follow-up of 370 days. The age-corrected decrease (mean: −3%, range: −27% to +19%) did not reach significance (p=0.09) but significantly correlated with the baseline TER (Spearman p=−0.62, p<0.001). Patients with low baseline TER showed an improved TER after PRRT, high decreases were only observed in individuals with high baseline TER. Pre-therapeutic TER data were inferior to plasma creatinine-derived GFR estimates in predicting late nephropathy. TER assessed by ^99mTc-MAG3­clearance prior to and during PRRT is not suitable as early predictor of renal injury and an increased risk for late nephropathy.

Initial Preclinical Evaluation of 18F-Fluorodeoxysorbitol PET as a Novel Functional Renal Imaging Agent

Accurate assessment of kidney function plays an essential role for optimal clinical decision making in a variety of diseases. The major intrinsic advantages of PET are superior spatial and temporal resolutions for quantitative tomographic renal imaging. 2-deoxy-2-¹⁸F-fluorodeoxysorbitol (¹⁸F-FDS) is an analog of sorbitol that is reported to be freely filtered at the renal glomerulus without reabsorption at the tubule. Furthermore, it can be synthesized via simple reduction of widely available ¹⁸F-FDG. We tested the feasibility of ¹⁸F-FDS renal PET imaging in rats.

METHODS

The systemic and renal distribution of ¹⁸F-FDS were determined by dynamic 35-min PET imaging (15 frames × 8 s, 26 frames × 30 s, 20 frames × 60 s) with a dedicated small-animal PET system and postmortem tissue counting in healthy rats. Distribution of coinjected ^99mTc-diethylenetriaminepentaacetic acid (DTPA) was also estimated as a reference. Plasma binding and in vivo stability of ¹⁸F-FDS were determined.

RESULTS

In vivo PET imaging visualized rapid excretion of the administrated ¹⁸F-FDS from both kidneys, with minimal tracer accumulation in other organs. Initial cortical tracer uptake followed by visualization of the collecting system could be observed with high contrast. Split-function renography curves were successfully obtained in healthy rats (the time of maximal concentration [T_max] right [R] = 2.8 ± 1.2 min, T_max left [L] = 2.9 ± 1.5 min, the time of half maximal concentration [T_1/2max] R = 8.8 ± 3.7 min, T_1/2max L = 11.1 ± 4.9 min). Postmortem tissue counting of ¹⁸F-FDS confirmed the high kidney extraction (kidney activities at 10, 30, and 60 min after tracer injection [percentage injected dose per gram]: 1.8 ± 0.7, 1.2 ± 0.1, and 0.5 ± 0.2, respectively) in a degree comparable to ^99mTc-DTPA (2.5 ± 1.0, 1.5 ± 0.2, and 0.8 ± 0.3, respectively). Plasma protein binding of ¹⁸F-FDS was low (<0.1%), and metabolic transformation was not detected in serum and urine.

CONCLUSION

In rat experiments, ¹⁸F-FDS demonstrated high kidney extraction and excretion, low plasma protein binding, and high metabolic stability as preferable properties for renal imaging. These preliminary results warrant further confirmatory studies in large animal models and clinical studies as a novel functional renal imaging agent, given the advantages of PET technology and broad tracer availability.