Comparison of [(177)Lu-DOTA(0),Tyr(3)]octreotate and [(177)Lu-DOTA(0),Tyr(3)]octreotide: which peptide is preferable for PRRT?

State of the art in nuclear medicine dose assessment

Basic calculational methods and models used in dose assessment for internal emitters in nuclear medicine are discussed in this overview. Methods for quantification of activity in clinical and preclinical studies also are discussed, and we show how to implement them in currently available dose calculational models. Current practice of the use of internal emitters in therapy also is briefly presented here. Some of the future challenges for dose assessment in nuclear medicine are discussed, including application of patient-specific dose calculational methods and the need for significant advances in radiation biology.

Neuroendocrine tumors of the gastro-entero-pancreatic system

Gastro-entero-pancreatic (GEP) neuroendocrine tumors (NETs) are rare neoplasms, although their prevalence has increased substantially over the past three decades. Moreover, there has been an increased clinical recognition and characterization of these neoplasms. They show extremely variable biological behavior and clinical course. Most NETs have endocrine function and secrete peptides and neuroamines that cause distinct clinical syndromes, including carcinoid syndrome; however, many are clinically silent until late presentation with mass effects. Investigation and management should be individualized for each patient, taking into account the likely natural history of the tumor and general health of the patient. Management strategies include surgery for cure or palliation, and a variety of other cytoreductive techniques, and medical treatment including chemotherapy, and biotherapy to control symptoms due to hormone release and tumor growth, with somatostatin analogues (SSAs) and alpha-interferon. New biological agents and somatostatin-tagged radionuclides are under investigation. Advances in the therapy and development of centers of excellence which coordinate multicenter studies, are needed to improve diagnosis, treatment and therefore survival of patients with GEP NETs.

Treatment with the radiolabeled somatostatin analog [177 Lu-DOTA 0,Tyr3]octreotate: toxicity, efficacy, and survival

PURPOSE

Despite the fact that most gastroenteropancreatic neuroendocrine tumors (GEPNETs) are slow-growing, median overall survival (OS) in patients with liver metastases is 2 to 4 years. In metastatic disease, cytoreductive therapeutic options are limited. A relatively new therapy is peptide receptor radionuclide therapy with the radiolabeled somatostatin analog [(177)Lu-DOTA(0),Tyr(3)]octreotate. Here we report on the toxicity and efficacy of this treatment, performed in over 500 patients.

PATIENTS AND METHODS

Patients were treated up to a cumulative dose of 750 to 800 mCi (27.8-29.6 GBq), usually in four treatment cycles, with treatment intervals of 6 to 10 weeks. Toxicity analysis was done in 504 patients, and efficacy analysis in 310 patients.

RESULTS

Any hematologic toxicity grade 3 or 4 occurred after 3.6% of administrations. Serious adverse events that were likely attributable to the treatment were myelodysplastic syndrome in three patients, and temporary, nonfatal, liver toxicity in two patients. Complete and partial tumor remissions occurred in 2% and 28% of 310 GEPNET patients, respectively. Minor tumor response (decrease in size > 25% and < 50%) occurred in 16%. Median time to progression was 40 months. Median OS from start of treatment was 46 months, median OS from diagnosis was 128 months. Compared with historical controls, there was a survival benefit of 40 to 72 months from diagnosis.

CONCLUSION

Treatment with [(177)Lu-DOTA(0),Tyr(3)]octreotate has few adverse effects. Tumor response rates and progression-free survival compare favorably to the limited number of alternative treatment modalities. Compared with historical controls, there is a benefit in OS from time of diagnosis of several years.

Multimodality management of a polyfunctional pancreatic endocrine carcinoma with markedly elevated serum vasoactive intestinal polypeptide and calcitonin levels

We present an unusual case of a 52-year-old woman with severe, uncontrollable, refractory diarrhea attributable to pancreatic endocrine carcinoma (ECA) with markedly elevated serum vasoactive intestinal polypeptide (VIP) and calcitonin levels. After initial correction of fluid and electrolyte abnormalities, the patient was treated with high-dose octreotide. Shortly thereafter, due to the intractable nature of her diarrhea, she underwent cytoreductive hepatic surgery. The pancreatosplenectomy specimen showed a poorly differentiated ECA of the distal pancreas, immunoreactive for synaptophysin, CD56, and S100 protein, with morphologically similar hepatic and lymph node metastases. Postoperatively, her diarrhea improved, along with decline in serum VIP and calcitonin levels. Systemic chemotherapy with etoposide and cisplatin did not result in any radiographic and biochemical improvement. Having radiologically stable disease with depot-octreotide and short-acting octreotide (Sandostatin), she was subjected to peptide receptor radiotherapy with [177Lu-DOTA0,Tyr]octreotate (LuTate) that resulted in marked clinical and biochemical improvement, along with dramatic reduction in the number and size of hepatic metastases. In summary, this is a unique case of metastatic VIP- and calcitonin-secreting pancreatic ECA with dramatic sustained clinical, biochemical, and objective tumor response to peptide receptor radionuclide therapy.

Transarterial chemoembolization of liver metastases from well differentiated gastroenteropancreatic endocrine tumors with doxorubicin-eluting beads: preliminary results

PURPOSE

To evaluate the feasibility, safety, and efficacy of transarterial chemoembolization (TACE) of progressive liver metastases from well differentiated gastroenteropancreatic endocrine (GEP) tumors with drug-eluting beads (DEBs).

MATERIALS AND METHODS

From June 2004 to July 2005, eight men and 12 women aged 34 to 75 years (mean +/- SD, 59 y +/- 12), including 13 patients with bilobar disease and seven with unilobar disease, underwent 34 sessions of TACE with DEBs (500-700 mum) loaded with doxorubicin. Morphologic response was evaluated with computed tomography (CT) at 1 and 3 months according to Response Evaluation Criteria In Solid Tumors. Clinical and laboratory data were also assessed.

RESULTS

The complete dose of 4 mL of DEBs loaded with 100 mg doxorubicin was injected during 22 TACE sessions and 1-3.5 mL of DEBs was injected during 12 TACE sessions. Three months after TACE, 16 of 20 patients (80%) exhibited a partial response, three (15%) had stable disease, and one (5%) had progressive disease. The mean size of the largest metastasis in each patient decreased from 42 mm +/- 24 before treatment (median, 39.5 mm) to 33 mm +/- 23 (median, 29 mm) 1 month after treatment and 30 mm +/- 21 (median, 26.5 mm) 3 months after treatment. After a median follow-up of 15 months (range, 6-24 months), nine patients' disease remained controlled without tumor progression and 10 patients had progressive disease. The median time to progression was 15 months. Postembolization syndrome lasted less than 7 days in 23 sessions (67%) and more than 7 days in seven sessions (22%), and no symptoms at all were observed in four sessions (11%). Peak aspartate aminotransferase, alanine aminotransferase, and bilirubin levels after TACE were 35-490 IU (mean, 125 IU +/- 77; normal, <35 IU), 20-440 IU (mean, 149 IU +/- 155; normal, <45 IU), and 8-90 mol/L (mean, 26 IU +/- 25; normal, <17 IU), respectively, at 2-3 days. In five patients, follow-up CT at 1 month revealed TACE-induced peripheral liver necrosis.

CONCLUSIONS

TACE with DEBs is well tolerated and appears effective. A comparative study with a standard TACE or transarterial embolization regimen is warranted to define the best protocol for transarterial treatment of GEP liver metastases.

Sporadically occurring functional pancreatic endocrine tumors: review of recent literature

PURPOSE OF REVIEW

Pancreatic neuroendocrine tumors are rare neoplasms often associated with a clinical syndrome. Their rarity makes a comprehensive study difficult at any single institution, while their uniqueness makes them desirable for investigation. This review summarizes recent information and advancements concerning pancreatic neuroendocrine tumor diagnosis, imaging characteristics, treatment algorithms, and staging.

RECENT FINDINGS

Insulinomas and gastrinomas comprise the majority of functional pancreatic neuroendocrine tumors. Advances in their identification and diagnostic evaluation, imaging techniques, and treatment algorithms are presented. Furthermore, a new staging classification system has been proposed which may significantly improve the ability to conduct future multi-institutional investigations on pancreatic neuroendocrine tumors.

SUMMARY

Although rare, a thorough understanding of pancreatic neuroendocrine tumors is essential for all physicians due to the wide variety of symptoms with which patients present. Currently, patients are often misdiagnosed for extended periods of time. This review summarizes the recently published literature about diagnosis, imaging, treatment, and staging of pancreatic neuroendocrine tumors.

Dimeric DOTA-alpha-melanocyte-stimulating hormone analogs: synthesis and in vivo characteristics of radiopeptides with high in vitro activity

Dimeric analogs of alpha-melanocyte-stimulating hormone (alpha-MSH) labeled with radiometals are potential candidates for diagnosis and therapy of melanoma by receptor-mediated tumor targeting. Both melanotic and amelanotic melanomas (over-)express the melanocortin-1 receptor (MC1-R), the target for alpha-MSH. In the past, dimerized MSH analogs have been shown to display increased receptor affinity compared to monomeric MSH, offering the possibility of improving the ratio between specific uptake of radiolabeled alpha-MSH by melanoma and nonspecific uptake by the kidneys. We have designed three linear dimeric analogs containing a slightly modified MSH hexapeptide core sequence (Nle-Asp-His-d-Phe-Arg-Trp) in parallel or antiparallel orientation, a short spacer, and the DOTA chelator for incorporation of the radiometal. In vitro, all three peptides were more potent ligands of the mouse B16-F1 melanoma cell melanocortin-1 receptor (MC1-R) than DOTA-NAPamide, which served as standard. The binding activity of DOTA-diHexa(NC-NC)-amide was 1.75-fold higher, that of diHexa(NC-NC)-Gly-Lys(DOTA)-amide was 3.37-fold higher, and that of DOTA-diHexa(CN-NC)-amide was 2.34-fold higher. Using human HBL melanoma cells, the binding activity of diHexa(NC-NC)-Gly-Lys(DOTA)-amide was sixfold higher than that of DOTA-NAPamide. Uptake by cultured B16-F1 cells was rapid and almost quantitative. In vivo, however, the data were less promising: tumor-to-kidney ratios 4 hr postinjection were 0.11 for [(111)In]DOTA-diHexa(NC-NC)-amide, 0.26 for diHexa(NC-NC)-Gly-Lys([(111)In]DOTA)-amide, and 0.36 for [(111)In]DOTA-diHexa(CN-NC)-amide, compared to 1.67 for [(111)In]DOTA-NAPamide. It appears that despite the higher affinity to the MC1-R of the peptide dimers and their excellent internalization in vitro, the uptake by melanoma tumors in vivo was lower, possibly because of reduced tissue penetration. More striking, however, was the marked increase of kidney uptake of the dimers, explaining the unfavorable ratios. In conclusion, although radiolabeled alpha-MSH dimer peptides display excellent receptor affinity and internalization, they are no alternative to the monomeric DOTA-NAPamide for in vivo application.

Results of individual patient dosimetry in peptide receptor radionuclide therapy with 177Lu DOTA-TATE and 177Lu DOTA-NOC

One of the few treatment options for inoperable neuroendocrine tumors (NET) is peptide receptor radiotherapy with somatostatin analogs. In this study, we compared the dosimetric parameter uptake, half-life (kinetics), and mean absorbed organ and tumor doses of (177)Lu DOTA-NOC and (177)Lu DOTA-TATE.

METHODS

Ninety-five (95) post-therapeutic dosimetric assessments using (177)Lu DOTA-TATE and 8 using (177)Lu DOTA-NOC in 69 patients with neuroendocrine tumors with high somatostatin receptor expression (verified by Ga-68 DOTA-NOC positron emission tomography/computed tomography) were analyzed. Dosimetric calculations were performed according to the Medical Internal Radiation Dose scheme.

RESULTS

(177)Lu DOTA-NOC showed a significantly (p < or = 0.05; sign test) higher uptake for whole-body and normal tissue, as compared to (177)Lu DOTA-TATE, leading to a significant higher whole-body dose of 0.07 mGy/ MBq for DOTA-NOC, as compared to 0.05 mGy/MBq for DOTA-TATE. Renal and spleen uptake and radiation doses were not significantly higher for DOTA-NOC. The uptake in tumor lesions and the mean absorbed tumor dose were higher for DOTA-TATE. The red marrow dose was approximately 0.2 Gy.

CONCLUSIONS

Our first results demonstrated that the higher in vitro affinity of DOTA-NOC leads to a higher uptake in normal tissues and, therefore, to an increase in the whole-body dose. The high interpatient variability of these results makes an individual patient dosimetry obligatory.

Peptide Receptor Radionuclide Therapy with radiolabelled somatostatin analogues in patients with somatostatin receptor positive tumours

Peptide Receptor Radionuclide Therapy (PRRT) with radiolabelled somatostatin analogues is a promising treatment option for patients with inoperable or metastasised neuroendocrine tumours. Symptomatic improvement may occur with all of the various (111)In, (90)Y, or (177)Lu-labelled somatostatin analogues that have been used. Since tumour size reduction was seldom achieved with (111)Indium labelled somatostatin analogues, radiolabelled somatostatin analogues with beta-emitting isotopes like (90)Y and (177)Lu were developed. Reported anti-tumour effects of [(90)Y-DOTA(0),Tyr(3)]octreotide vary considerably between various studies: Tumour regression of 50% or more was achieved in 9 to 33% (mean 22%). With [(177)Lu-DOTA(0),Tyr(3)]octreotate treatments, tumour regression of 50% or more was achieved in 28% of patients and tumour regression of 25 to 50% in 19% of patients, stable disease was demonstrated in 35% and progressive disease in 18%. Predictive factors for tumour remission were high tumour uptake on somatostatin receptor scintigraphy and limited amount of liver metastases. The side-effects of PRRT are few and mostly mild, certainly when using renal protective agents: Serious side-effects like myelodysplastic syndrome or renal failure are rare. The median duration of the therapy response for [(90)Y-DOTA(0),Tyr(3)]octreotide and [(177)Lu-DOTA(0),Tyr(3)]octreotate is 30 months and more than 36 months respectively. Lastly, quality of life improves significantly after treatment with [(177)Lu-DOTA(0),Tyr(3)]octreotate. These data compare favourably with the limited number of alternative treatment approaches, like chemotherapy. If more widespread use of PRRT is possible, such therapy might become the therapy of first choice in patients with metastasised or inoperable gastroenteropancreatic neuroendocrine tumours. Also the role in somatostatin receptor expressing non-GEP tumours, like metastasised paraganglioma/pheochromocytoma and non-radioiodine-avid differentiated thyroid carcinoma might become more important.

Nuclear imaging of neuroendocrine tumours

The diagnosis of neuroendocrine tumours (NETs) and monitoring of therapy in many patients relies mainly on morphological imaging techniques such as computed tomography (CT), ultrasound (US) and magnetic resonance imaging (MRI). However, functional imaging modalities--such as somatostatin receptor scintigraphy (SRS)--have great impact on patient management by providing tools for better staging of the disease, visualization of occult tumour, and evaluation of eligibility for somatostatin analogue treatment. Positron emission tomography (PET) using (18)F-fluoro-deoxy-glucose (FDG) is a powerful functional modality for oncological imaging. Unfortunately, FDG is not accumulated in NETs except in the case of dedifferentiated tumours and tumours with high proliferative activity. Based on the concept of amine precursor uptake and decarboxylation (APUD), the (18)F- and (11)C-labelled amine precursors L-dihydroxyphenylalanine and 5-hydroxy-L-tryptophan (5-HTP) have been utilized for PET imaging of NETs. In comparative studies of patients with a variety of NETs, (11)C5-HTP-PET proved better than CT and SRS by visualizing additional small lesions. With carbidopa premedication orally before (11)C5-HTP-PET examination the tumour uptake could be increased and the urinary radioactivity concentration considerably reduced. This concept may also be applied to (18)F-L-DOPA-PET, a method which in a limited number of studies has gained additional diagnostic information in NET patients compared to SRS and morphological imaging. (68)Ga is available from an in-house generator and has been utilized for labelling of somatostatin analogues for PET imaging of NETs with promising results in a small number of patients. However, SRS is an established functional imaging method for patients with NETs, whereas the role for PET in the clinical routine needs further evaluation in comparative studies in larger groups of patients.