Lessons on Tumour Response: Imaging during Therapy with (177)Lu-DOTA-octreotate. A Case Report on a Patient with a Large Volume of Poorly Differentiated Neuroendocrine Carcinoma

Neuroendocrine Carcinomas with Atypical Proliferation Index and Clinical Behavior: A Systematic Review

BACKGROUND

Highly proliferative (G3) neuroendocrine neoplasms are divided into well differentiated tumors (NETs) and poorly differentiated carcinomas (NECs), based on the morphological appearance. This systematic review aims to evaluate the clinicopathological features and the treatment response of the NEC subgroup with a Ki67 labeling index (LI) < 55%.

METHODS

A literature search was performed using MEDLINE, Cochrane Library, and Scopus between December 2019 and April 2020, last update in October 2020. We included studies reporting data on the clinicopathological characteristics, survival, and/or therapy efficacy of patients with NECs, in which the Ki67 LI was specified.

RESULTS

8 papers were included, on a total of 268 NEC affected patients. NECs with a Ki67 LI < 55% have been reported in patients of both sexes, mainly of sixth decade, pancreatic origin, and large-cell morphology. The prevalent treatment choice was chemotherapy, followed by surgery and, in only one study, peptide receptor radionuclide therapy. The subgroup of patients with NEC with a Ki67 LI < 55% showed longer overall survival and progression free survival and higher response rates than the subgroup of patients with a tumor with higher Ki67 LI (≥55%).

CONCLUSIONS

NECs are heterogeneous tumors. The subgroup with a Ki67 LI < 55% has a better prognosis and should be treated and monitored differently from NECs with a Ki67 LI ≥ 55%.

A Peptide Meets a Radionuclide to Combat a Rare Tumor

Background: Neuroendocrine carcinomas (NECs) are rare malignancies with limited treatment options beyond surgery. Peptide receptor radionuclide therapy (PRRT) is a process by which a somatostatin analog (octreotate) is combined with a chelator (DOTA) and a radionuclide (lutetium-177 [177Lu-dotatate]). This therapy targets receptors on neuroendocrine cells, causing internalization of the radionuclide by the tumor cell, which results in cellular damage and apoptosis. Case Report: We describe the clinical and therapeutic course of a 69-year-old male with a metastatic rectal NEC in whom progressive disease was noted after multiple therapies were attempted. After PRRT with 177Lu-dotatate, the patient was asymptomatic and demonstrated a near-complete radiologic response. Conclusion: This case illustrates that treatment with PRRT may improve the outcome of patients with metastatic rectal NEC. Our case highlights the importance of further research into the use of PRRT in patients with a Ki-67 <55% and uptake on somatostatin receptor imaging.

(Radio)Theranostic Patient Management in Oncology Exemplified by Neuroendocrine Neoplasms, Prostate Cancer, and Breast Cancer

The role of nuclear medicine in the management of oncological patients has expanded during last two decades. The number of radiopharmaceuticals contributing to the realization of theranostics/radiotheranostics in the context of personalized medicine is increasing. This review is focused on the examples of targeted (radio)pharmaceuticals for the imaging and therapy of neuroendocrine neoplasms (NENs), prostate cancer, and breast cancer. These examples strongly demonstrate the tendency of nuclear medicine development towards personalized medicine.

Current Treatment Options in Gastroenteropancreatic Neuroendocrine Carcinoma

Poorly differentiated gastroenteropancreatic neuroendocrine carcinomas (GEPNECs) are a rare neoplasm with a bleak prognosis. Currently there are little prospective data available for optimal treatment. This review discusses the current available regimens and the future direction for the treatment of GEPNECs. Treatment plans for GEPNECs are often adapted from those devised for small cell lung cancer; however, differences in these malignancies exist, and GEPNECs require their own treatment paradigms. As such, current first-line treatment for GEPNECs is platinum-based chemotherapy with etoposide. Studies show that response rate and overall survival remain comparable between cisplatin and carboplatin versus etoposide and irinotecan; however, prognosis remains poor, and more efficacious therapy is needed to treat this malignancy. Additional first-line and second-line treatment options beyond platinum-based chemotherapy have also been investigated and may offer further treatment options, but again with suboptimal outcomes. Recent U.S. Food and Drug Administration approval of peptide receptor radionuclide therapy in low- and intermediate-grade neuroendocrine tumors may open the door for further research in its usefulness in GEPNECs. Additionally, the availability of checkpoint inhibitors lends promise to the treatment of GEPNECs. This review highlights the lack of large, prospective studies that focus on the treatment of GEPNECs. There is a need for randomized control trials to elucidate optimal treatment regimens specific to this malignancy. IMPLICATIONS FOR PRACTICE: There are limited data available for the treatment of poorly differentiated gastroenteropancreatic neuroendocrine carcinomas (GEPNECs) because of the rarity of this malignancy. Much of the treatment regimens used in practice today come from research in small cell lung cancer. Given the poor prognosis of GEPNECs, it is necessary to have treatment paradigms specific to this malignancy. The aim of this literature review is to summarize the available first- and second-line GEPNEC therapy, outline future treatments, and highlight the vast gap in the literature.

Prospective observational study of 177Lu-DOTA-octreotate therapy in 200 patients with advanced metastasized neuroendocrine tumours (NETs): feasibility and impact of a dosimetry-guided study protocol on outcome and toxicity

PURPOSE

Peptide receptor radionuclide therapy in patients with neuroendocrine tumours has yielded promising results. This prospective study investigated the feasibility of dosimetry of the kidneys and bone marrow during therapy and its impact on efficacy and outcome.

METHODS

The study group comprised 200 consecutive patients with metastasized somatostatin receptor-positive neuroendocrine tumours progressing on standard therapy or not suitable for other therapeutic options. A treatment cycle consisted of 7.4 GBq ¹⁷⁷Lu-DOTA-octreotate with co-infusion of a mixed amino acid solution, and cycles were repeated until the absorbed dose to the kidneys reached 23 Gy or there were other reasons for stopping therapy. The Ki-67 index was ≤2% in 47 patients (23.5%), 3-20% in 121 (60.5%) and >20% in 16 (8%).

RESULTS

In 123 patients (61.5%) the absorbed dose to the kidneys reached 23 Gy with three to nine cycles during first-line therapy; in no patient was a dose to the bone marrow of 2 Gy reached. The best responses (according to RECIST 1.1) were a complete response (CR) in 1 patient (0.5%), a partial response (PR) in 47 (23.5%), stable disease (SD) in 135 (67.5%) and progressive disease (PD) in 7 (3.5%). Median progression-free survival was 27 months (95% CI 22-30 months) in all patients, 33 months in those in whom the absorbed dose to the kidneys reached 23 Gy and 15 months in those in whom it did not. Median overall survival (OS) was 43 months (95% CI 39-53 months) in all patients, 54 months in those in whom the absorbed dose to the kidneys reached 23 Gy and 25 months in those in whom it did not. Median OS was 60 months in patients with a best response of PR or CR, 42 months in those with SD and 16 months in those with PD. Three patients (1.5%) developed acute leukaemia, 1 patient (0.5%) chronic leukaemia (unconfirmed) and 30 patients (15%) grade 3 or 4 bone marrow toxicity. Eight patients (4%) developed grade 2 kidney toxicity and one patient (0.5%) grade 4 kidney toxicity.

CONCLUSIONS

Dosimetry-based therapy with ¹⁷⁷Lu-DOTA-octreotate is feasible. Patients in whom the absorbed dose to the kidneys reached 23 Gy had a longer OS than those in whom it did not. Patients with CR/PR had a longer OS than those with SD. Bone marrow dosimetry did not predict toxicity.

The Effect of Total Tumor Volume on the Biologically Effective Dose to Tumor and Kidneys for 177Lu-Labeled PSMA Peptides

The aim of this work was to simulate the effect of prostate-specific membrane antigen (PSMA)-positive total tumor volume (TTV) on the biologically effective doses (BEDs) to tumors and organs at risk in patients with metastatic castration-resistant prostate cancer who are undergoing ¹⁷⁷Lu-PSMA radioligand therapy. Methods: A physiologically based pharmacokinetic model was fitted to the data of 13 patients treated with ¹⁷⁷Lu-PSMA I&T (a PSMA inhibitor for imaging and therapy). The tumor, kidney, and salivary gland BEDs were simulated for TTVs of 0.1-10 L. The activity and peptide amounts leading to an optimal tumor-to-kidneys BED ratio were also investigated. Results: When the TTV was increased from 0.3 to 3 L, the simulated BEDs to tumors, kidneys, parotid glands, and submandibular glands decreased from 22 ± 15 to 11.0 ± 6.0 Gy_1.49, 6.5 ± 2.3 to 3.7 ± 1.4 Gy_2.5, 11.0 ± 2.7 to 6.4 ± 1.9 Gy_4.5, and 10.9 ± 2.7 to 6.3 ± 1.9 Gy_4.5, respectively (where the subscripts denote that an α/β of 1.49, 2.5, or 4.5 Gy was used to calculate the BED). The BED to the red marrow increased from 0.17 ± 0.05 to 0.32 ± 0.11 Gy₁₅ For patients with a TTV of more than 0.3 L, the optimal amount of peptide was 273 ± 136 nmol and the optimal activity was 10.4 ± 4.4 GBq. Conclusion: This simulation study suggests that in patients with large PSMA-positive tumor volumes, higher activities and peptide amounts can be safely administered to maximize tumor BEDs without exceeding the tolerable BED to the organs at risk.

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.

Renal Function Assessment During Peptide Receptor Radionuclide Therapy

Theranostics labeled with Y-90 or Lu-177 are highly efficient therapeutic approaches for the systemic treatment of various cancers including neuroendocrine tumors and prostate cancer. Peptide receptor radionuclide therapy (PRRT) has been used for many years for metastatic or inoperable neuroendocrine tumors. However, renal and hematopoietic toxicities are the major limitations for this therapeutic approach. Kidneys have been considered as the "critical organ" because of the predominant glomerular filtration, tubular reabsorption by the proximal tubules, and interstitial retention of the tracers. Severe nephrotoxity, which has been classified as grade 4-5 based on the "Common Terminology Criteria on Adverse Events," was reported in the range from 0%-14%. There are several risk factors for renal toxicity; patient-related risk factors include older age, preexisting renal disease, hypertension, diabetes mellitus, previous nephrotoxic chemotherapy, metastatic lesions close to renal parenchyma, and single kidney. There are also treatment-related issues, such as choice of radionuclide, cumulative radiation dose to kidneys, renal radiation dose per cycle, activity administered, number of cycles, and time interval between cycles. In the literature, nephrotoxicity caused by PRRT was documented using different criteria and renal function tests, from serum creatinine level to more accurate and sophisticated methods. Generally, serum creatinine level was used as a measure of kidney function. Glomerular filtration rate (GFR) estimation based on serum creatinine was preferred by several authors. Most commonly used formulas for estimation of GFR are "Modifications of Diet in Renal Disease" (MDRD) equation and "Cockcroft-Gault" formulas. However, more precise methods than creatinine or creatinine clearance are recommended to assess renal function, such as GFR measurements using Tc-99m-diethylenetriaminepentaacetic acid (DTPA), Cr-51-ethylenediaminetetraacetic acid (EDTA), or measurement of Tc-99m-MAG3 clearance, particularly in patients with preexisting risk factors for long-term nephrotoxicity. Proximal tubular reabsorption and interstitial retention of tracers result in excessive renal irradiation. Coinfusion of positively charged amino acids, such as l-lysine and l-arginine, is recommended to decrease the renal retention of the tracers by inhibiting the proximal tubular reabsorption. Furthermore, nephrotoxicity may be reduced by dose fractionation. Patient-specific dosimetric studies showed that renal biological effective dose of <0Gy was safe for patients without any risk factors. A renal threshold value <28Gy was recommended for patients with risk factors. Despite kidney protection, renal function impairment can occur after PRRT, especially in patients with risk factors and high single or cumulative renal absorbed dose. Therefore, patient-specific dosimetry may be helpful in minimizing the renal absorbed dose while maximizing the tumor dose. In addition, close and accurate renal function monitoring using more precise methods, rather than plasma creatinine levels, is essential to diagnose the early renal functional changes and to follow-up the renal function during the treatment.

The prognostic influence of the proliferative discordance in metastatic pancreatic neuroendocrine carcinoma revealed by peptide receptor radionuclide therapy: Case report and review of literature

RATIONALE

Pancreatic neuroendocrine tumors (pNET) are rare slowly growing tumors with a high metastatic potential. Peptide receptor radionuclide therapy (PRRT) with radiolabeled analogues has been developed as a new tool for the management of metastatic well-differentiated (grade 1 and 2) neuroendocrine tumors expressing somatostatin receptor (SSTR2). Chemotherapy is the mainstay in the management of grade 3 (G3) unresectable pancreatic neuroendocrine carcinoma (pNEC). To date, no study has evaluated the efficacy of PRRT in such tumors.

DIAGNOSES AND INTERVENTIONS

We describe a case of a progressive G3 pNEC with huge liver metastases successfully treated with PRRT (Lu DOTATATE).

OUTCOMES

Complete remission was obtained for 3 years. Indeed, the mitotic index was low (as G2 tumors) but with a very high Ki-67 index (45%-70%). Such discordance between the proliferative markers should consider the use of PRRT before chemotherapy in unresectable metastatic G3 tumors expressing SSTR2.

LESSONS

This case supports the hypotheses highlighting the heterogeneity of G3 pNEC. The latter should be subdivided into 2 distinct categories: proliferation-discordant (well differentiated) and concordant (poorly differentiated) NEC. PRRT could be suggested for the former group before the conventional chemotherapy.

Parametric Net Influx Rate Images of 68Ga-DOTATOC and 68Ga-DOTATATE: Quantitative Accuracy and Improved Image Contrast

⁶⁸Ga-DOTATOC and ⁶⁸Ga-DOTATATE are radiolabeled somatostatin analogs used for the diagnosis of somatostatin receptor-expressing neuroendocrine tumors (NETs), and SUV measurements are suggested for treatment monitoring. However, changes in net influx rate (K_i) may better reflect treatment effects than those of the SUV, and accordingly there is a need to compute parametric images showing K_i at the voxel level. The aim of this study was to evaluate parametric methods for computation of parametric K_i images by comparison to volume of interest (VOI)-based methods and to assess image contrast in terms of tumor-to-liver ratio. Methods: Ten patients with metastatic NETs underwent a 45-min dynamic PET examination followed by whole-body PET/CT at 1 h after injection of ⁶⁸Ga-DOTATOC and ⁶⁸Ga-DOTATATE on consecutive days. Parametric K_i images were computed using a basis function method (BFM) implementation of the 2-tissue-irreversible-compartment model and the Patlak method using a descending aorta image-derived input function, and mean tumor K_i values were determined for 50% isocontour VOIs and compared with K_i values based on nonlinear regression (NLR) of the whole-VOI time-activity curve. A subsample of healthy liver was delineated in the whole-body and K_i images, and tumor-to-liver ratios were calculated to evaluate image contrast. Correlation (R²) and agreement between VOI-based and parametric K_i values were assessed using regression and Bland-Altman analysis. Results: The R² between NLR-based and parametric image-based (BFM) tumor K_i values was 0.98 (slope, 0.81) and 0.97 (slope, 0.88) for ⁶⁸Ga-DOTATOC and ⁶⁸Ga-DOTATATE, respectively. For Patlak analysis, the R² between NLR-based and parametric-based (Patlak) tumor K_i was 0.95 (slope, 0.71) and 0.92 (slope, 0.74) for ⁶⁸Ga-DOTATOC and ⁶⁸Ga-DOTATATE, respectively. There was no bias between NLR and parametric-based K_i values. Tumor-to-liver contrast was 1.6 and 2.0 times higher in the parametric BFM K_i images and 2.3 and 3.0 times in the Patlak images than in the whole-body images for ⁶⁸Ga-DOTATOC and ⁶⁸Ga-DOTATATE, respectively. Conclusion: A high R² and agreement between NLR- and parametric-based K_i values was found, showing that K_i images are quantitatively accurate. In addition, tumor-to-liver contrast was superior in the parametric K_i images compared with whole-body images for both ⁶⁸Ga-DOTATOC and ⁶⁸Ga DOTATATE.

Effect of calculation method on kidney dosimetry in 177Lu-octreotate treatment

BACKGROUND

¹⁷⁷Lu-octreotate is an effective treatment modality for patients with metastatic neuroendocrine tumors. The kidney is a critical dose-limiting organ in that modality. We investigated the absorbed doses in the kidney and compared whole kidney volume (WKV) and small (4 cm³) volume of the kidney (SV) methods. We also evaluated a new calculation method that was based on two single photon emission computed tomography/computed tomography (SPECT/CT) scans.

METHODS

Absorbed radiation doses in the kidneys were calculated for 24 patients with neuroendocrine tumors. All patients received four cycles of ¹⁷⁷Lu-octreotate given at eight-week intervals with a mean activity of 7.1 GBq (range 3.28-8.79 GBq). Absorbed doses and half-lives were calculated by the WKV and SV methods. Dosimetry was determined for the cortex and medulla in the first treatment cycle.

RESULTS

The mean absorbed radiation dose was 0.44 ± 0.15 Gy/GBq for the WKV method and, 0.74 ± 0.28 Gy/GBq for the SV method. Three patients had a 20% increase of the absorbed dose over the four treatment cycles for the WKV method compared to eight patients for the SV method. The mean absorbed dose in the medulla was 0.62 ± 0.27 Gy/GBq, whereas the mean absorbed dose in the cortex was 0.41 ± 0.22 Gy/GBq. Both regions had similar half-lives. Patients who received lower activities for medical reasons still had similar absorbed doses to kidneys compared to those who received the full activities. Our study indicates that absorbed doses can be calculated reliably using two SPECT/CT scans, at 24 and 168 hours after each treatment.

CONCLUSIONS

Absorbed doses in the kidneys from systemic radionuclide therapy that are measured by the WKV method and SV method cannot be directly compared. There were regional differences within kidneys for the uptake of ¹⁷⁷Lu-octreotate. Two SPECT/CTs are sufficient for kidney dosimetry based on our new calculation method.

Current and Future Theranostic Applications of the Lipid-Calcium-Phosphate Nanoparticle Platform

Over the last four years, the Lipid-Calcium-Phosphate (LCP) nanoparticle platform has shown success in a wide range of treatment strategies, recently including theranostics. The high specific drug loading of radiometals into LCP, coupled with its ability to efficiently encapsulate many types of cytotoxic agents, allows a broad range of theranostic applications, many of which are yet unexplored. In addition to providing an overview of current medical imaging modalities, this review highlights the current theranostic applications for LCP using SPECT and PET, and discusses potential future uses of the platform by comparing it with both systemically and locally delivered clinical radiotherapy options as well as introducing its applications as an MRI contrast agent. Strengths and weaknesses of LCP and of nanoparticles in general are discussed, as well as caveats regarding the use of fluorescence to determine the accumulation or biodistribution of a probe.

Renal function affects absorbed dose to the kidneys and haematological toxicity during ¹⁷⁷Lu-DOTATATE treatment

Purpose

Peptide receptor radionuclide therapy (PRRT) has become an important treatment option in the management of advanced neuroendocrine tumours. Long-lasting responses are reported for a majority of treated patients, with good tolerability and a favourable impact on quality of life. The treatment is usually limited by the cumulative absorbed dose to the kidneys, where the radiopharmaceutical is reabsorbed and retained, or by evident haematological toxicity. The aim of this study was to evaluate how renal function affects (1) absorbed dose to the kidneys, and (2) the development of haematological toxicity during PRRT treatment.

Methods

The study included 51 patients with an advanced neuroendocrine tumour who received ¹⁷⁷Lu-DOTATATE treatment during 2006 – 2011 at Sahlgrenska University Hospital in Gothenburg. An average activity of 7.5 GBq (3.5 – 8.2 GBq) was given at intervals of 6 – 8 weeks on one to five occasions. Patient baseline characteristics according to renal and bone marrow function, tumour burden and medical history including prior treatment were recorded. Renal and bone marrow function were then monitored during treatment. Renal dosimetry was performed according to the conjugate view method, and the residence time for the radiopharmaceutical in the whole body was calculated.

Results

A significant correlation between inferior renal function before treatment and higher received renal absorbed dose per administered activity was found (p < 0.01). Patients with inferior renal function also experienced a higher grade of haematological toxicity during treatment (p = 0.01). The residence time of ¹⁷⁷Lu in the whole body (range 0.89 – 3.0 days) was correlated with grade of haematological toxicity (p = 0.04) but not with renal absorbed dose (p = 0.53).

Conclusion

Patients with inferior renal function were exposed to higher renal absorbed dose per administered activity and developed a higher grade of haematological toxicity during ¹⁷⁷Lu-DOTATATE treatment. The study confirms the tolerability of PRRT in patients with an advanced neuroendocrine tumour but indicates that patients with inferior renal function are at risk of being exposed to higher absorbed doses to normal tissue on treatment.

Dosimetry of [(177)Lu]-DO3A-VS-Cys(40)-Exendin-4 - impact on the feasibility of insulinoma internal radiotherapy

[(68)Ga]-DO3A-VS-Cys(40)-Exendin-4 has been shown to be a promising imaging candidate for targeting glucagon like peptide-1 receptor (GLP-1R). In the light of radiotheranostics and personalized medicine the (177)Lu-labelled analogue is of paramount interest. In this study we have investigated the organ distribution of [(177)Lu]-DO3A-VS-Cys(40)-Exendin-4 in rat and calculated human dosimetry parameters in order to estimate the maximal acceptable administered radioactivity, and thus potential applicability of [(177)Lu]-DO3A-VS-Cys(40)-Exendin-4 for internal radiotherapy of insulinomas. Nine male and nine female Lewis rats were injected with [(177)Lu]-DO3A-VS-Cys(40)-Exendin-4 for ex vivo organ distribution study at nine time points. The estimation of human organ/total body absorbed and total effective doses was performed using Organ Level Internal Dose Assessment Code software (OLINDA/EXM 1.1). Six more rats (male: n = 3; female: n = 3) were scanned by single photon emission tomography and computed tomography (SPECT-CT). The renal function and potential cell dysfunction were monitored by creatinine ISTAT and glucose levels. The fine uptake structure of kidney and pancreas was investigated by ex vivo autoradiography. Blood clearance and washout from most of the organs was fast. The kidney was the dose-limiting organ with absorbed dose of 5.88 and 6.04 mGy/MBq, respectively for female and male. Pancreatic beta cells demonstrated radioactivity accumulation. Renal function and beta cell function remained unaffected by radiation. The absorbed dose of [(177)Lu]-DO3A-VS-Cys(40)-Exendin-4 to kidneys may limit the clinical application of the agent. However, hypothetically, kidney protection and peptidase inhibition may allow reduction of kidney absorbed dose and amplification of tumour absorbed doses.

Gastroenteropancreatic high-grade neuroendocrine carcinoma

Gastroenteropancreatic (GEP) neuroendocrine neoplasms are classified as low-grade, intermediate-grade, and high-grade tumors based on morphologic criteria and the proliferation rate. Most studies have been conducted in patients with well differentiated (low-grade to intermediate-grade) neuroendocrine tumors. Data are substantially scarcer on poorly differentiated, high-grade neuroendocrine carcinoma (NEC), which includes the entities of small cell carcinoma and large cell NEC. A literature search of GEP-NEC was performed. Long-term survival was poor even among patients who presented with localized disease. Several studies highlighted heterogeneity within the high-grade NEC category and a need for the further identification of discreet prognostic and predictive groups. Tumors with a Ki-67 proliferation index <55% were less responsive to platinum-based chemotherapy, and patients with such tumors or with well differentiated morphology had better survival than patients who had tumors with poorly differentiated morphology or a higher Ki-67 index. Treatment options beyond platinum-based chemotherapy are emerging. A revision of the World Health Organization high-grade NEC classification seems to be necessary based on recent data. Platinum-based chemotherapy may not be the optimal treatment for patients who have GEP-NEC with a moderately high proliferation rate. Adequate diagnostic and prognostic stratifications constitute the basis for future progress.

Somatostatin receptor-based molecular imaging and therapy for neuroendocrine tumors

Neuroendocrine tumors (NETs) are tumors originated from neuroendocrine cells in the body. The localization and the detection of the extent of NETs are important for diagnosis and treatment, which should be individualized according to the tumor type, burden, and symptoms. Molecular imaging of NETs with high sensitivity and specificity is achieved by nuclear medicine method using single photon-emitting and positron-emitting radiopharmaceuticals. Somatostatin receptor imaging (SRI) using SPECT or PET as a whole-body imaging technique has become a crucial part of the management of NETs. The radiotherapy with somatostatin analogues labeled with therapeutic beta emitters, such as lutetium-177 or yttrium-90, has been proved to be an option of therapy for patients with unresectable and metastasized NETs. Molecular imaging can deliver an important message to improve the outcome for patients with NETs by earlier diagnosis, better choice of the therapeutic method, and evaluation of the therapeutic response.

PET imaging of inflammation biomarkers

Inflammation plays a significant role in many disease processes. Development in molecular imaging in recent years provides new insight into the diagnosis and treatment evaluation of various inflammatory diseases and diseases involving inflammatory process. Positron emission tomography using (18)F-FDG has been successfully applied in clinical oncology and neurology and in the inflammation realm. In addition to glucose metabolism, a variety of targets for inflammation imaging are being discovered and utilized, some of which are considered superior to FDG for imaging inflammation. This review summarizes the potential inflammation imaging targets and corresponding PET tracers, and the applications of PET in major inflammatory diseases and tumor associated inflammation. Also, the current attempt in differentiating inflammation from tumor using PET is also discussed.

Individualized dosimetry of kidney and bone marrow in patients undergoing 177Lu-DOTA-octreotate treatment

The organs at risk in radionuclide therapy with (177)Lu-octreotate are the bone marrow and the kidneys. The primary aim of this study was to develop an individualized dosimetry protocol for the bone marrow. The secondary aim was to identify those patients, undergoing fractionated therapy with 7.4 GBq/cycle, who first reached an accumulated dose of either 2 Gy to the bone marrow or 23 Gy to the kidneys.

METHODS

Two hundred patients with metastatic neuroendocrine tumors with high somatostatin receptor expression were included. After the administration of 7.4 GBq of (177)Lu-octreotate, blood samples were drawn 6 times within the first 24 h. In 50 patients, additional blood samples were obtained at 96 and 168 h. Moreover, urine was collected from 30 patients during the first 24 h. Planar whole-body and SPECT/CT images over the abdomen were acquired at 24, 96, and 168 h after the infusion. Calculation of the absorbed radiation dose to the bone marrow was based on blood and urinary activity curves combined with organ-based analysis of the whole-body images. The absorbed dose to the kidney was calculated from the pharmacokinetic data obtained from SPECT/CT.

RESULTS

For a single cycle of 7.4 GBq, the absorbed dose to the bone marrow and the kidney ranged from 0.05 to 0.4 Gy and from 2 to 10 Gy, respectively. In 197 of 200 patients, the kidneys accumulated an absorbed dose of 23 Gy before the bone marrow reached 2 Gy. Between 2 and 10 cycles of (177)Lu-octreotate could be administered before the upper dose limit for the individual patient was reached.

CONCLUSION

A method based on repeated whole-body imaging in combination with blood and urinary activity data over time was developed to determine the absorbed dose to the bone marrow. The dose-limiting organ was the kidney in 197 of 200 patients. In 50% of the patients, more than 4 cycles of 7.4 GBq of (177)Lu-octreotate could be administered, whereas 20% of the subjects were treated with fewer than 4 cycles. Individualized absorbed dose calculation is essential to optimize the therapy.

Molecular imaging and radiotherapy: theranostics for personalized patient management

This theme issue presents current achievements in the development of radioactive agents, pre-clinical and clinical molecular imaging, and radiotherapy in the context of theranostics in the field of oncology.