Long-term prognostic factors for PRRT in neuroendocrine tumors

One-day dual-tracer examination in neuroendocrine neoplasms: a real advantage of low activity LAFOV PET imaging

PURPOSE

Somatostatin receptor (SSTR)-PET is crucial for effective treatment stratification of neuroendocrine neoplasms (NENs). In highly proliferating or poorly differentiated NENs, dual-tracer approaches using additional [18F]FDG PET can effectively identify SSTR-negative disease, usually requiring separate imaging sessions. We evaluated the feasibility of a one-day dual-tracer imaging protocol with a low activity [18F]FDG PET followed by an SSTR-PET using the recently introduced [18F]SiFAlin-TATE tracer in a long axial field-of-view (LAFOV) PET/CT scanner and its implications in patient management.

METHODS

Twenty NEN patients were included in this study. Initially, a low activity [18F]FDG PET was performed (0.5 ± 0.01 MBq/kg; PET scan 60 min p.i.). After 4.2 ± 0.09 h after completion of the [18F]FDG PET, a standard activity of [18F]SiFAlin-TATE was administered (3.0 MBq/kg; PET scan 90 min p.i.). To ensure the quantification accuracy of the second scan, we evaluated the potential impact of residual [18F]FDG activity by segmenting organs with minimal physiological SSTR-tracer uptake, such as the brain and myocardium, and assessing the activity concentrations (ACTs) of tumor lesions. Residual tumor lesion ACTs of [18F]FDG were calculated by factoring fluorine-18 decay, identifying a maximum residual ACT of 15% (R15%). To account for increased [18F]FDG trapping over time, higher residual ACTs of 20% (R20%) were considered. These simulated [18F]FDG ACTs were compared with those measured in the second PET scan with [18F]SiFAlin-TATE. The influence of the dual-tracer PET/CT results on therapeutic strategies was evaluated.

RESULTS

[18F]FDG cerebral uptake significantly decreased in the subsequent SSTR-PET (mean uptake [18F]FDG: SUVmean 6.0 ± 0.4; mean uptake in [18F]SiFAlin-TATE PET: SUVmean 0.2 ± 0.01; p < 0.0001); with similar results recorded for the myocardium. Simulated residual [18F]FDG ACTs represented only a minimal percentage of ACTs measured in the tumor lesions from the second PET scan (R15%: mean 5.2 ± 0.9% and R20%: mean 6.8 ± 1.2%), indicating only minimal residual activity of [18F]FDG that might interfere with the second PET scan using [18F]SiFAlin-TATE and preserved semi-quantification of the latter. Dual-tracer PET/CT findings directly influenced changes in therapy plans in eleven (55%) of the examined patients.

CONCLUSION

LAFOV PET scanners enable a one-day dual-tracer protocol, providing diagnostic image quality while preserving the semi-quantification of two 18F-labeled radiotracers, potentially simplifying the assessment of tumor biology and improving the clinical patient management while reducing logistical challenges. Additionally, low-activity PET imaging facilitates one-day dual-tracer PET examinations.

Histologic Ex Vivo Validation of the [18F]SITATE Somatostatin Receptor PET Tracer

Radiolabeled somatostatin analogs (SSAs), such as [68Ga]Ga-DOTA SSAs, have transformed imaging and therapeutic strategies. However, their use is constrained by the high cost of generators and their short half-life. In contrast, [18F]SITATE presents a promising alternative, offering the advantage of a longer half-life than 68Ga, along with the cost-effectiveness of cyclotron-based production. This study evaluated the first histologic ex vivo validation of [18F]SITATE. Methods: This study retrospectively included 47 patients (57% male; mean age, 66.9 ± 14.9 y) with histologically confirmed well-differentiated neuroendocrine neoplasms who underwent [18F]SITATE PET followed by surgery within 4 mo. Lesion uptake was quantified using SUVmean, SUVpeak, SUVmax, and tumor-to-liver ratio (TLR). Histologic somatostatin receptor (SSTR) type 2 expression was determined using histological scores (H-scores), with thresholds defining SSTR scores 1-3. The accuracy of PET imaging for preoperative metastatic detection was evaluated against surgical histology. Results: PET imaging demonstrated a significant correlation between [18F]SITATE uptake (SUVmean and TLR) and SSTR type 2 H-scores (r = 0.618 and 0.622, respectively; P < 0.0001). SSTR score 3 correlated with increased SUVmean and TLR (P < 0.0001). Among 35 patients with primary resection and lymphadenectomy, PET achieved a sensitivity of 73.9% and specificity of 100%. Conclusion: [18F]SITATE PET imaging strongly correlates with histologic SSTR expression, demonstrating utility in staging and guiding therapeutic decisions in neuroendocrine neoplasms. This 18F-labeled tracer shows specificity comparable to historical [68Ga]Ga-DOTA SSA data, whereas an increase in sensitivity for the detection of locoregional metastases appears possible. Further head-to-head comparisons of [18F]SITATE with traditional [68Ga]Ga-DOTA SSA and histologic validation are warranted to optimize its diagnostic accuracy and clinical impact.

Prognostic value of interim [68Ga]Ga-DOTA-TOC PET/CT in patients with neuroendocrine tumour who underwent peptide receptor radionuclide therapy

OBJECTIVES

This study evaluated the prognostic value of basal and interim [68Ga]Ga-DOTA-TOC PET/CT in patients with locally advanced or metastatic neuroendocrine tumour (NET) who received peptide receptor radionuclide therapy (PRRT).

METHODS

Patients with NET who received PRRT with [177Lu]Lu-DOTA-TATE at our institution were retrospectively reviewed. Among them, patients who underwent both basal and interim (after two cycles of PRRT) [68Ga]Ga-DOTA-TOC PET/CT were included. Alongside clinicopathologic parameters, PET parameters of maximum standardised uptake value (SUVmax), tumour-to-liver ratio (TLR), whole tumour volume (WTV) and total receptor expression (TRE: WTV multiplied by mean standardised uptake value) were obtained from basal and interim [68Ga]Ga-DOTA-TOC PET/CT, and their proportional changes (∆) were assessed for associations with progression-free survival (PFS) using Kaplan-Meier analysis, log-rank tests, and a Cox proportional-hazards regression model.

RESULTS

Twenty-four patients were finally included (10 men and 14 women, median age of 56.5 years, age range 32-74 years). Among them, 16 patients (66.7%) experienced disease progression. In univariate analysis, high ∆WTV (≥ -10%, hazard ratio [HR] = 3.053 [1.003-9.289], p = 0.049) and high ∆TRE (≥ -21%, HR = 3.567 [1.144-11.122], p = 0.028) were significantly associated with shorter PFS. In multivariate analyses adjusted for WHO grade, high ∆WTV (HR = 3.345 [1.055-10.601], p = 0.043) and high ∆TRE (HR = 3.894 [1.194-12.695], p = 0.024) were significant predictors of shorter PFS.

CONCLUSION

The study demonstrates that basal and interim [68Ga]Ga-DOTA-TOC PET/CT scans, through proportional changes in WTV and TRE, effectively predict PFS in neuroendocrine tumour patients receiving PRRT.

KEY POINTS

Question Peptide receptor radionuclide therapy is utilised for patients with somatostatin receptor-positive well-differentiated neuroendocrine tumours; however, prognostic predictors are not well established. Findings Progression-free survival was significantly associated with the proportional change in whole tumour volume and total receptor expression between basal and interim [68Ga]Ga-DOTA-TOC PET/CT. Clinical relevance Interim [68Ga]Ga-DOTA-TOC PET/CT can serve as a valuable imaging method to predict prognosis of peptide receptor radionuclide therapy.

Beyond similarities: overall survival and prognostic insights from [¹⁷⁷Lu]Lu-DOTATOC therapy in neuroendocrine tumors

PURPOSE

Therapy with [177Lu]Lu-DOTATATE is well established for neuroendocrine tumors (NET), but its production generates [177mLu], raising concerns about waste disposal due to its longer half-life. In contrast, [177mLu] is not formed during [177Lu]Lu-DOTATOC production. However, data on overall survival (OS) and prognostic factors for [177Lu]Lu-DOTATOC remain limited, and its efficacy compared to [177Lu]Lu-DOTATATE is uncertain. This study aimed to analyze OS and radiological response in NET patients treated with [177Lu]Lu-DOTATOC.

METHODS

Monocentric, retrospective analysis of 141 patients with NET (grading: 21% G1, 71% G2, 4% G3, 4% grading unknown; primary: 48% small intestine (SI-NET); 27% pancreas (P-NET); 9% colon/rectum; 1% stomach, 7% lung; 9% CUP-NET) receiving PRRT with [177Lu]Lu-DOTATOC. Cox and logistic regression were used to identify prognostic factors for OS or risk of primary progression.

RESULTS

Death from any cause was observed in 85 of 141 patients (60.3%). Median OS was 55.2 months (SI NET G1-G2: 62.7 months; P-NET G1-G2: 41.2 months; NET G3: 26.3 months). Multivariable Cox regression identified baseline De Ritis Ratio (p < 0.001), ALP (p < 0.001), CgA (p < 0.001) and prior therapy with mTOR-inhibitors (p = 0.005) as significant prognostic factors of OS. Overall response rate was 12% and disease control rate was 72%. In multivariable logistic regression, primary tumor location (p = 0.04) and CgA (p = 0.01) were significant prognostic factors for higher risk of primary progression.

CONCLUSION

The analysis of OS from routine clinical practice shows that PRRT with [177Lu]Lu-DOTATOC is an effective treatment option for NET patients, while generating minimal [177mLu]. The evaluated prognostic factors could help to identify patients who particularly benefit from shorter follow-up intervals.

Low-activity [18F]-somatostatin receptor (SSTR) imaging using [18F]SiTATE on a long axial field-of-view PET/CT scanner

PURPOSE

18F-labelled somatostatin receptor tracers have recently gained popularity due to their better spatial resolution, longer half-life and lower costs compared to 68Ga-labeled tracers. The aim of this study was to evaluate the impact and limitations of reduced administered activities of [18F]SiTATE on image quality, lesion detectability and quantitative PET parameters in a long axial field-of-view (LAFOV) PET/CT scanner.

METHODS

Twenty-four patients with histologically confirmed neuroendocrine tumor, who underwent clinically indicated [18F]SiTATE PET/CT examination (3.0 MBq/kg, 5 min PET scan time) on a Siemens Biograph Vision Quadra LAFOV PET/CT, were included retrospectively in this study. PET list-mode data were rebinned for shorter frame durations to simulate 5 min scans with lower activities of injected radiotracer. A comparison of image reconstruction in high sensitivity (HS) and ultra-high sensitivity mode (UHS) mode was performed. Subjective image quality, noise and lesion detectability of n = 122 lesions were rated using a 5-point Likert scale. The molecular tumor volume (MTV), signal-to-noise ratio (SNR), tumor-to-liver activity concentration ratio (TLR) and standardized uptake values (SUV) were analyzed.

RESULTS

Subjective image quality decreased with simulated reduction of injected activity with generally superior ratings in the UHS mode compared to the HS mode. Despite a reduction to 1 MBq/kg of [18F]SiTATE all lesions were still detected while at 0.25 MBq/kg lesion detectability decreased to 70% (HS) and 93% (UHS). Only minor changes in SUVmean and TLR were detected with reduced activity. However, reduced activities led to an increase in SUVSD, which in turn caused a decrease in SNR (at 1 MBq/kg: 7.3 in HS and 9.0 in UHS mode and an increase in deviation of the MTV.

CONCLUSION

Reducing the administered activity of injected [18F]SiTATE by 66% to 1 MBq/kg (HS & UHS) is feasible in a LAFOV PET/CT scanner, maintaining clinically diagnostic image quality without statistically significant deviations in PET uptake parameters and MTV. Furthermore, in low activity [18F]SiTATE PET/CT, the UHS mode improves image quality and noise as well as lesion detectability compared to HS mode, further reinforcing the clinical benefits of this recently introduced reconstruction mode.

Challenges in developing response evaluation criteria for peptide receptor radionuclide therapy: A consensus report from the European Neuroendocrine Tumor Society Advisory Board Meeting 2022 and the ENETS Theranostics Task Force

Assessing the response to systemic therapy in neuroendocrine tumors (NET) is challenging since morphological imaging response is often delayed and not necessarily reflective of clinical benefit. Peptide receptor radionuclide therapy (PRRT) has a complex mechanism of action, further complicating response assessment. In response to these challenges, the European Neuroendocrine Tumor Society (ENETS) Theranostics Task Force conducted a statement-based survey among experts to identify the current landscape and unmet needs in PRRT response assessment. The survey, presented at the 2022 ENETS Advisory Board (AB) meeting in Vienna, was completed by 70% of AB members, most of whom (81%) were from ENETS Centers of Excellence (CoE). It comprised a set of 13 questions with two substatements in three questions. Six (46%) of the statements achieved more than 75% agreement, while five (39%) additional statements reached over 60% consensus. Key points from the survey include: AB members agreed that lesions deemed equivocal on computed tomography (CT) or magnetic resonance imaging (MRI) should be characterized by somatostatin receptor (SST) positron emission tomography (PET)/CT before being designated as target lesions. It was agreed that interim response assessments should occur after the second or third PRRT cycle. Over half (54%) preferred using both conventional cross-sectional imaging (CT and/or MRI) and hybrid imaging (SST PET/CT) for this purpose. Almost all AB members supported further response assessment 3 months after the final PRRT cycle. A majority (62%) preferred using a combination of conventional cross-sectional imaging and SST PET/CT. For cases showing equivocal progression (ambiguous lesions or nontarget lesions) on CT and/or MRI, further confirmation using SST PET/CT was recommended. A significant majority (74%) preferred assessing pseudo-progression and delayed response by combining SST PET with diagnostic CT and/ or MRI. Though just below the 75% consensus threshold, there was substantial agreement on selecting target lesions based on SST PET/CT uptake intensity and homogeneity. Sixty-nine percent noted the importance of documenting and closely following heterogeneity in lesions in liver, lymph nodes, primary tumors, or other organs. As to the statement on parameters for new response criteria, AB members recommended exploring maximum standard unit value, tumor-to-background ratio, Hounsfield Unit (Choi Criteria), total tumor burden, and novel serum or molecular markers for future response evaluation criteria. Sixty-five percent supported the use of a single SST PET/CT for response assessment of NET lesions treated with PRRT. These findings highlight the importance of integrating advanced imaging techniques and recognizing the need for more nuanced criteria in assessing the efficacy of PRRT in NET patients. This approach aims to enhance the accuracy of treatment monitoring and improve patient outcomes.

Surgery enhances the effectiveness of peptide receptor radionuclide therapy in metastatic gastroenteropancreatic neuroendocrine tumors

BACKGROUND

With the advent of peptide receptor radionuclide therapy, the timing and sequence of surgery in the treatment of metastatic gastroenteropancreatic neuroendocrine tumors merits further study. We hypothesized that surgery before peptide receptor radionuclide therapy might enhance its effectiveness in patients with metastatic gastroenteropancreatic neuroendocrine tumors.

METHODS

Eighty-nine patients with metastatic well-differentiated gastroenteropancreatic neuroendocrine tumors treated with 177Lutetium-dotatate peptide receptor radionuclide therapy between 2018 and 2023 were included. Fifty-six patients underwent surgery (primary tumor resection and/or liver debulking) before peptide receptor radionuclide therapy and 33 patients did not. Primary outcome was progression-free survival according to Response Evaluation Criteria in Solid Tumors. Pretreatment dotatate positron emission tomography/computed tomography was used to calculate tumor volumes.

RESULTS

The surgery and no-surgery groups were well-matched. Median progression-free survival after peptide receptor radionuclide therapy was 15.6 months (interquartile range, 9.1-22.7 months) in the no-surgery group compared with 26.1 months (interquartile range, 12.7-38.1 months) in the surgery group (P = .04). On subgroup analysis, median progression-free survival was 18.1 months (interquartile range, 11.9-38.4 months) in patients who underwent primary tumor resection only compared with 26.2 months (interquartile range, 14.0-38.1 months) in patients who underwent liver debulking (P = .04). Tumor volume was lowest in patients who underwent liver debulking (median 146.07 mL3) compared with no surgery (median 626.42 mL3) (P = .001). On univariable analysis, a tumor volume <138.8 mL3 was associated with longer progression-free survival (hazard ratio, 2.03; 95% confidence interval, 0.95-4.34, P = .05), with a median progression-free survival of 38.1 months (interquartile range, 16.9-41.3 months) compared with 17.8 months (interquartile range, 10.8-28.7 months).

CONCLUSION

Surgery may enhance the effectiveness of 177Lutetium-dotatate in the treatment of metastatic well-differentiated gastroenteropancreatic neuroendocrine tumors. This positive effect may be the result of a lower tumor volume in patients after surgery. Our findings fortify the concept of using surgical debulking to improve systemic therapies such as peptide receptor radionuclide therapy.

Adverse Events of Radioligand Therapy in Patients with Progressive Neuroendocrine Neoplasms: The Biggest Eastern European Prospective Study

BACKGROUND

Neuroendocrine neoplasms (NENs) are neoplastic tumors developing in every part of the body, mainly in the gastrointestinal tract and pancreas. Their treatment involves the surgical removal of the tumor and its metastasis, long-acting somatostatin analogs, chemotherapy, targeted therapy, and radioligand therapy (RLT).

MATERIALS AND METHODS

A total of 127 patients with progressive neuroendocrine neoplasms underwent RLT-4 courses, administered every 10 weeks-with the use of 7.4 GBq [177Lu]Lu-DOTA-TATE or tandem therapy with 1.85 GBq [177Lu]Lu-DOTA-TATE and 1.85 GBq [90Y]Y-DOTA-TATE. Assessment of short- and long-term complications, as well as the calculation of progression-free survival (PFS) and overall survival (OS) were performed.

RESULTS

RLT caused a statistically but not clinically significant decrease in blood morphology parameters during both short- and long-term observations. Glomerular filtration rate (GFR) significantly decreased only in a long-term observation after RLT; however, it was clinically acceptable. Computed predictions of progression-free survival (PFS) and overall survival (OS) indicated that five years post-RLT, there is a 74% chance of patients surviving, with only a 58.5% likelihood of disease progression.

CONCLUSIONS

Computed predictions of PFS and OS confirmed treatment efficiency and good patient survival. RLT should be considered a safe and reliable line of treatment for patients with progressive NENs as it causes only a low number of low-grade adverse events.

Radionuclide Theranostics in Neuroendocrine Neoplasms: An Update

PURPOSE OF REVIEW

This paper aims to address the latest findings in neuroendocrine tumor (NET) theranostics, focusing on new evidence and future directions of combined diagnosis with positron emission tomography (PET) and treatment with peptide receptor radionuclide therapy (PRRT).

RECENT FINDINGS

Following NETTER-1 trial, PRRT with [177Lu]Lu-DOTATATE was approved by FDA and EMA and is routinely employed in advanced G1 and G2 SST (somatostatin receptor)-expressing NET. Different approaches have been proposed so far to improve the PRRT therapeutic index, encompassing re-treatment protocols, combinations with other therapies and novel indications. Molecular imaging holds a potential added value in characterizing disease biology and heterogeneity using different radiopharmaceuticals (e.g., SST and FDG) and may provide predictive and prognostic parameters. Response assessment criteria are still an unmet need and new theranostic pairs showed preliminary encouraging results. PRRT for NET has become a paradigm of modern theranostics. PRRT holds a favorable toxicity profile, and it is associated with a prolonged time to progression, reduction of symptoms, and improved patients' quality of life. In light of further optimization, different new strategies have been investigated, along with the development of new radiopharmaceuticals.

Theranostics and artificial intelligence: new frontiers in personalized medicine

The field of theranostics is rapidly advancing, driven by the goals of enhancing patient care. Recent breakthroughs in artificial intelligence (AI) and its innovative theranostic applications have marked a critical step forward in nuclear medicine, leading to a significant paradigm shift in precision oncology. For instance, AI-assisted tumor characterization, including automated image interpretation, tumor segmentation, feature identification, and prediction of high-risk lesions, improves diagnostic processes, offering a precise and detailed evaluation. With a comprehensive assessment tailored to an individual's unique clinical profile, AI algorithms promise to enhance patient risk classification, thereby benefiting the alignment of patient needs with the most appropriate treatment plans. By uncovering potential factors unseeable to the human eye, such as intrinsic variations in tumor radiosensitivity or molecular profile, AI software has the potential to revolutionize the prediction of response heterogeneity. For accurate and efficient dosimetry calculations, AI technology offers significant advantages by providing customized phantoms and streamlining complex mathematical algorithms, making personalized dosimetry feasible and accessible in busy clinical settings. AI tools have the potential to be leveraged to predict and mitigate treatment-related adverse events, allowing early interventions. Additionally, generative AI can be utilized to find new targets for developing novel radiopharmaceuticals and facilitate drug discovery. However, while there is immense potential and notable interest in the role of AI in theranostics, these technologies do not lack limitations and challenges. There remains still much to be explored and understood. In this study, we investigate the current applications of AI in theranostics and seek to broaden the horizons for future research and innovation.