Towards Single Time Point Image-Based Dosimetry of 177Lu-PSMA-617 Therapy

Radiopharmaceutical therapies (RPTs) with Lutetium-177 prostate-specific membrane antigen (PSMA) ligands have demonstrated promising results for the treatment of metastatic castration-resistant prostate cancer (mCRPC). The lack of absorbed dose and effect relationships currently prevents from patient-specific activity personalization. To ease the implementation of dosimetry in routine clinic workflow of RPT, simplified methods such as single time point (STP) instead of multiple time point (MTP) imaging protocols are required. This work aims at assessing differences in time-integrated activity (TIA) of STP versus MTP image-based dosimetry for ¹⁷⁷Lu-PSMA-617 therapy. Methods: 20 mCRPC patients with MTP quantitative ¹⁷⁷Lu-SPECT imaging data (~24h, 48h, 72h post administration) available on first and second ¹⁷⁷Lu-PSMA-617 therapy cycles were included in this study. Time-activity-curves were fitted for kidneys and lesions to derive effective half-lives and yield reference TIA. STP approaches involved the formula by Hänscheid (STPH) and a prior information method (STPprior) that uses the effective half-lives from the first therapy cycle. All time points were considered for the STP approaches. Percentage differences (PD) in TIA between STP and MTP was compared for the second therapy cycle. Results: Using STPH at 48h p.i. for the kidneys had -1.3±5.6% difference against MTP, while STPprior showed a PD of 4.6±6.2%. Smallest average differences for the 56 investigated individual lesions were found using the STPprior approach at 48h p.i. with only 0.4±14.9%, while STPH at 72h p.i. had smallest PD of -1.9±14.8%. Conclusion: STP dosimetry for ¹⁷⁷Lu-PSMA-617 therapy using a single SPECT/CT at 48h or 72h is feasible with a difference of <±20% compared against MTP. Both, STPH and STPprior have demonstrated their validity. We believe this finding can increase the adoption of dosimetry and facilitate implementation in routine clinical RPT workflows. Doing so will ultimately enable the finding of dose-effective relationships based on fixed therapy activities that could in future allow for absorbed dose based RPT activity personalization.

Dosimetry and optimal scan time of [18F]SiTATE-PET/CT in patients with neuroendocrine tumours

PURPOSE

Radiolabelled somatostatin analogues targeting somatostatin receptors (SSR) are well established for combined positron emission tomography/computer tomography (PET/CT) imaging of neuroendocrine tumours (NET). [18F]SiTATE has recently been introduced showing high image quality, promising clinical performance and improved logistics compared to the clinical reference standard 68Ga-DOTA-TOC. Here we present the first dosimetry and optimal scan time analysis.

METHODS

Eight NET patients received a [18F]SiTATE-PET/CT (250 ± 66 MBq) with repeated emission scans (10, 30, 60, 120, 180 min after injection). Biodistribution in normal organs and SSR-positive tumour uptake were assessed. Dosimetry estimates for risk organs were determined using a combined linear-monoexponential model, and by applying 18F S-values and reference target masses for the ICRP89 adult male or female (OLINDA 2.0). Tumour-to-background ratios were compared quantitatively and visually between different scan times.

RESULTS

After 1 h, normal organs showed similar tracer uptake with only negligible changes until 3 h post-injection. In contrast, tracer uptake by tumours increased progressively for almost all types of metastases, thus increasing tumour-to-background ratios over time. Dosimetry resulted in a total effective dose of 0.015 ± 0.004 mSv/MBq. Visual evaluation revealed no clinically relevant discrepancies between later scan times, but image quality was rated highest in 60 and 120 min images.

CONCLUSION

[18F]SiTATE-PET/CT in NET shows overall high tumour-to-background ratios from 60 to 180 min after injection and an effective dose comparable to 68Ga-labelled alternatives. For clinical use of [18F]SiTATE, the best compromise between image quality and tumour-to-background contrast is reached at 120 min, followed by 60 min after injection.

Correlation of an Index-Lesion-Based SPECT Dosimetry Method with Mean Tumor Dose and Clinical Outcome after 177Lu-PSMA-617 Radioligand Therapy

Background: Dosimetry can tailor prostate-specific membrane-antigen-targeted radioligand therapy (PSMA-RLT) for metastatic castration-resistant prostate cancer (mCRPC). However, whole-body tumor dosimetry is challenging in patients with a high tumor burden. We evaluate a simplified index-lesion-based single-photon emission computed tomography (SPECT) dosimetry method in correlation with clinical outcome. Methods: 30 mCRPC patients were included (median 71 years). The dosimetry was performed for the first cycle using quantitative ¹⁷⁷Lu-SPECT. The response was evaluated using RECIST 1.1 and PERCIST criteria, as well as changes in PSMA-positive tumor volume (PSMA-TV) in post-therapy PSMA-PET and biochemical response according to PSA changes after two RLT cycles. Results: Mean tumor doses as well as index-lesion doses were significantly higher in PERCIST responders compared to non-responders (10.2 ± 12.0 Gy/GBq vs. 4.0 ± 2.9 Gy/GBq, p = 0.03 and 13.7 ± 14.2 Gy/GBq vs. 5.9 ± 4.4 Gy/GBq, p = 0.04, respectively). No significant differences in mean tumor and index lesion doses were observed between responders and non-responders according to RECIST 1.1, PSMA-TV, and biochemical response criteria. Conclusion: Compared to mean tumor doses on a patient level, single index-lesion-based SPECT dosimetry correlates equally well with the response to PSMA-RLT according to PERCIST criteria and may represent a fast and feasible dosimetry approach for clinical routine.

Detection of Splenic Tissue Using 99mTc-Labelled Denatured Red Blood Cells Scintigraphy—A Quantitative Single Center Analysis

Background: Red blood cells (RBC) scintigraphy can be used not only for detection of bleeding sites, but also of spleen tissue. However, there is no established quantitative readout. Therefore, we investigated uptake in suspected splenic lesions in direct quantitative correlation to sites of physiologic uptake in order to objectify the readout. Methods: 20 patients with Tc-99m-labelled RBC scintigraphy and SPECT/low-dose CT for assessment of suspected splenic tissue were included. Lesions were rated as vital splenic or non-splenic tissue, and uptake and physiologic uptake of bone marrow, pancreas, and spleen were then quantified using a volume-of-interest based approach. Hepatic uptake served as a reference. Results: The median uptake ratio was significantly higher in splenic (2.82 (range, 0.58–24.10), n = 47) compared to other lesions (0.49 (0.01–0.83), n = 7), p < 0.001, and 5 lesions were newly discovered. The median pancreatic uptake was 0.09 (range 0.03–0.67), bone marrow 0.17 (0.03–0.45), and orthotopic spleen 14.45 (3.04–29.82). Compared to orthotopic spleens, the pancreas showed lowest uptake (0.09 vs. 14.45, p = 0.004). Based on pancreatic uptake we defined a cutoff (0.75) to distinguish splenic from other tissues. Conclusion: As the uptake in extra-splenic regions is invariably low compared to splenules, it can be used as comparator for evaluating suspected splenic tissues.

Evaluation of MRI in the diagnostic accuracy of extrahepatic metastases in neuroendocrine tumors in comparison with the reference standard somatostatin-receptor-PET/CT

Purpose

The aim of this study was to compare the diagnostic performance of different sets of MR sequences in detecting extrahepatic disease of NETs on routine liver magnetic resonance imaging (MRI).

Method

One hundred twenty-seven patients with NETs with and without hepatic and extrahepatic metastases who underwent liver MRI and SSTR-PET/CT were retrospectively analyzed. Two radiologists evaluated in consensus in four sessions: (1) non-contrast T1w+T2w (NC), (2) NC+DWI, (3) NC+ contrast-enhanced T1w (CE), and (4) NC+DWI+CE the presence and number of metastases (lymph nodes, bone, peritoneal surface, lung base, and abdominal organ). Sensitivity, specificity, positive, and negative predictive value for detection of metastases were calculated for each session in a patient-based manner; detection and error rates were calculated for lesion-based analysis. Comparison between the MR-sessions and positron emission tomography-computed tomography (PET/CT) was performed with the McNemar test.

Results

Regarding all 1,094 lesions detected in PET/CT, NC+DWI, and NC, CE+DWI identified most true-positive lesions 779 (71%) and 775 (71%), respectively. Patient-based analysis revealed significantly higher sensitivity by NC+DWI (85%) than NC and NC+CE (p = 0.011 and 0.004, respectively); the highest specificity was reached by NC+CE+DWI (100%). Site-based analysis revealed highest detection rates for lymph node metastases for NC+DWI and NC, CE+DWI (73 and 76%, respectively); error rates were lower for NC, CE+DWI with 5% compared with 17% (NC+DWI). Detection rates for bone metastases were similarly high in NC+DWI and NC, CE+DWI (75 and 74%, respectively), while CE showed no benefit. For peritoneal metastases highest sensitivity was reached by NC+DWI (67%).

Conclusion

The combination of NC+DWI showed better sensitivities than the combination of NC+CE. NC+DWI showed similar, sometimes even better sensitivities than NC+CE+DWI, but with lower specificities.

Validation of the standardization framework SSTR-RADS 1.0 for neuroendocrine tumors using the novel SSTR‑targeting peptide [18F]SiTATE

OBJECTIVES

Somatostatin receptor positron emission tomography/computed tomography (SSTR-PET/CT) using [68Ga]-labeled tracers is a widely used imaging modality for neuroendocrine tumors (NET). Recently, [18F]SiTATE, a SiFAlin tagged [Tyr3]-octreotate (TATE) PET tracer, has shown great potential due to favorable clinical characteristics. We aimed to evaluate the reproducibility of Somatostatin Receptor-Reporting and Data System 1.0 (SSTR-RADS 1.0) for structured interpretation and treatment planning of NET using [18F]SiTATE.

METHODS

Four readers assessed [18F]SiTATE-PET/CT of 95 patients according to the SSTR-RADS 1.0 criteria at two different time points. Each reader evaluated up to five target lesions per scan. The overall scan score and the decision on peptide receptor radionuclide therapy (PRRT) were considered. Inter- and intra-reader agreement was determined using the intraclass correlation coefficient (ICC).

RESULTS

The ICC analysis on the inter-reader agreement using SSTR-RADS 1.0 for identical target lesions (ICC ≥ 85%), overall scan score (ICC ≥ 90%), and the decision to recommend PRRT (ICC ≥ 85%) showed excellent agreement. However, significant differences were observed in recommending PRRT among experienced readers (ER) (p = 0.020) and inexperienced readers (IR) (p = 0.004). Compartment-based analysis demonstrated good to excellent inter-reader agreement for most organs (ICC ≥ 74%), except for lymph nodes (ICC ≥ 53%).

CONCLUSION

SSTR-RADS 1.0 represents a highly reproducible and consistent framework system for stratifying SSTR-targeted PET/CT scans, even using the novel SSTR-ligand [18F]SiTATE. Some inter-reader variability was observed regarding the evaluation of uptake intensity prior to PRRT as well as compartment scoring of lymph nodes, indicating that those categories require special attention during further clinical validation and might be refined in a future SSTR-RADS version 1.1.

CLINICAL RELEVANCE STATEMENT

SSTR-RADS 1.0 is a consistent framework for categorizing somatostatin receptor-targeted PET/CT scans when using [18F]SiTATE. The framework serves as a valuable tool for facilitating and improving the management of patients with NET.

KEY POINTS

SSTR-RADS 1.0 is a valuable tool for managing patients with NET. SSTR-RADS 1.0 categorizes patients with showing strong agreement across diverse reader expertise. As an alternative to [68Ga]-labeled PET/CT in neuroendocrine tumor imaging, SSTR-RADS 1.0 reliably classifies [18F]SiTATE-PET/CT.

The Association between the Body Mass Index, Chronic Obstructive Pulmonary Disease and SUV of the Non-Tumorous Lung in the Pretreatment [18F]FDG-PET/CT of Patients with Lung Cancer

Background: A debate persists on the prognostic value of the pre-therapeutic standardized uptake value (SUV) of non-tumorous lung tissue for the risk assessment of therapy-related pneumonitis, with most studies lacking significant correlation. However, the influence of patient comorbidities on the pre-therapeutic lung SUV has not yet been systematically evaluated. Thus, we aimed to elucidate the association between comorbidities, biological variables and lung SUVs in pre-therapeutic [18F]FDG-PET/CT. Methods: In this retrospective study, the pre-therapeutic SUV in [18F]FDG-PET/CT was measured in non-tumorous areas of both lobes of the lung. SUVMEAN, SUVMAX and SUV95 were compared to a multitude of patient characteristics and comorbidities with Spearman's correlation analysis, followed by a Bonferroni correction and multilinear regression. Results: In total, 240 patients with lung cancer were analyzed. An elevated BMI was significantly associated with increased SUVMAX (β = 0.037, p < 0.001), SUVMEAN (β = 0.017, p < 0.001) and SUV95 (β = 0.028, p < 0.001). Patients with chronic obstructive pulmonary disease (COPD) showed a significantly decreased SUVMAX (β = -0.156, p = 0.001), SUVMEAN (β = -0.107, p < 0.001) and SUV95 (β = -0.134, p < 0.001). Multiple other comorbidities did not show a significant correlation with the SUV of the non-tumorous lung. Conclusions: Failure to consider the influence of BMI and COPD on the pre-therapeutic SUV measurements may lead to an erroneous interpretation of the pre-therapeutic SUV and subsequent treatment decisions in patients with lung cancer.

The impact of endocrine disrupting chemicals on adrenal corticosteroids - A systematic review of epidemiological studies

BACKGROUND

The role of endocrine disrupting chemicals (EDCs) in the development of metabolic syndrome has gained increasing recognition in recent years. The underlying mechanisms are largely unresolved. Disruption of corticosteroid action and hypothalamic-pituitary-adrenal (HPA) axis are considered possible mechanisms.

OBJECTIVE

To summarise epidemiological studies investigating an association between EDC concentration and altered levels of corticosteroids and the adrenocorticotropic hormone (ACTH).

METHODS

Following the PRISMA guidelines, we searched PubMed and the Cochrane Library for epidemiological studies published from database inception until April 1st, 2024. Various groups of EDCs were evaluated with the prerequisite of direct measurement of the chemical, a metabolite, or biomarker.

RESULTS

We identified 2094 articles. After removing duplicates and screening, 27 studies were included. Studies focused predominantly on glucocorticoids (n = 26) compared to mineralocorticoids (n = 5) and ACTH (n = 2). The most studied EDCs were pesticides (n = 9) and phthalates (n = 8). Significant associations between the concentrations of specific EDCs and hormone levels were found in all but three studies. Only one study described an association between EDCs, and hormone concentration and metabolic features.

CONCLUSION

There is clear evidence for the impact of specific EDCs on plasma corticosteroid concentrations in different age groups worldwide, however, results varied according to EDC class, study population and study methodology. Further research combining EDC and hormone concentrations, and clinical features, complemented by experimental investigations to study cell mechanisms, is needed to gain holistic knowledge of EDCs' influence on glucocorticoid- and mineralocorticoid-related disorders.

Correlation of early-phase β-amyloid positron-emission-tomography and neuropsychological testing in patients with Alzheimer's disease

PURPOSE

Clinical staging in individuals with Alzheimer's disease (AD) typically relies on neuropsychological testing. Recognizing the imperative for an objective measure of clinical AD staging, regional perfusion in early-phase β-amyloid-PET may aid as a cost-efficient index for the assessment of neurodegeneration severity in patients with Alzheimer's disease.

METHODS

Regional perfusion deficits in early-phase β-amyloid-PET as well as neuropsychological testing (max. 90 days delay) were evaluated in 82 patients with biologically defined AD according to the ATN classification. In reference to the Braak staging system patients were classified into the groups stage0, stageI-II+, stageI-IV+, stageI-VI+, and stageatypical+ according to regional perfusion deficits in regions of interest (ROIs) published by the Alzheimer's Disease Neuroimaging Initiative. Multiple regression analysis controlling for age, gender, and education was used to evaluate the association of regional z-scores on perfusion-phase PET with clinical scores for all patients and with annual decline of cognitive performance in 23 patients with follow-up data.

RESULTS

Patients classified as stage0 and stageI-II+ demonstrated significantly superior neuropsychological performance compared to those classified as stageI-IV+ and stageI-VI+. Lower cognitive performance was associated with decreased perfusion in early-phase β-amyloid-PET globally and regionally, with the most pronounced association identified in the left temporal lobe. Mean z-scores on early-phase PET in temporal and parietal regions offered a robust prediction of future annual decline in MMSE and sum scores of the CERAD-Plus (Consortium to Establish a Registry for Alzheimer's Disease) test battery.

CONCLUSION

Regional and global perfusion deficits in early-phase β-amyloid-PET can serve as an objective index of neurodegeneration severity and may act as prognostic markers of future cognitive decline in AD.

Assessment of perfusion deficit with early phases of [18F]PI-2620 tau-PET versus [18F]flutemetamol-amyloid-PET recordings

PURPOSE

Characteristic features of amyloid-PET (A), tau-PET (T), and FDG-PET (N) can serve for the A/T/N classification of neurodegenerative diseases. Recent studies showed that the early, perfusion-weighted phases of amyloid- or tau-PET recordings serve to detect cerebrometabolic deficits equally to FDG-PET, therefore providing a surrogate of neuronal injury. As such, two channels of diagnostic information can be obtained in the setting of a single PET scan. However, there has hitherto been no comparison of early-phase amyloid- and tau-PET as surrogates for deficits in perfusion/metabolism. Therefore, we undertook to compare [¹⁸F]flutemetamol-amyloid-PET and [¹⁸F]PI-2620 tau-PET as "one-stop shop" dual purpose tracers for the detection of neurodegenerative disease.

METHODS

We obtained early-phase PET recordings with [¹⁸F]PI-2620 (0.5-2.5 min p.i.) and [¹⁸F]flutemetamol (0-10 min p.i.) in 64 patients with suspected neurodegenerative disease. We contrasted global mean normalized images (SUVr) in the patients with a normal cohort of 15 volunteers without evidence of increased pathology to β-amyloid- and tau-PET examinations. Regional group differences of tracer uptake (z-scores) of 246 Brainnetome volumes of interest were calculated for both tracers, and the correlations of the z-scores were evaluated using Pearson's correlation coefficient. Lobar compartments, regions with significant neuronal injury (z-scores <  - 3), and patients with different neurodegenerative disease entities (e.g., Alzheimer's disease or 4R-tauopathies) served for subgroup analysis. Additionally, we used partial regression to correlate regional perfusion alterations with clinical scores in cognition tests.

RESULTS

The z-scores of perfusion-weighted images of both tracers showed high correlations across the brain, especially in the frontal and parietal lobes, which were the brain regions with pronounced perfusion deficit in the patient group (R = 0.83 ± 0.08; range, 0.61-0.95). Z-scores of individual patients correlated well by region (R = 0.57 ± 0.15; range, 0.16-0.90), notably when significant perfusion deficits were present (R = 0.66 ± 0.15; range, 0.28-0.90).

CONCLUSION

The early perfusion phases of [¹⁸F]PI-2620 tau- and [¹⁸F]flutemetamol-amyloid-PET are roughly equivalent indices of perfusion defect indicative of regional and lobar neuronal injury in patients with various neurodegenerative diseases. As such, either tracer may serve for two diagnostic channels by assessment of amyloid/tau status and neuronal activity.

Quantitative SSTR-PET/CT: a potential tool for predicting everolimus response in neuroendoctine tumour patients

BACKGROUND

This study aimed to assess 68Ga-DOTA-TATE (-TOC) PET/CT quantitative parameters in monitoring and predicting everolimus response in neuroendocrine tumor (NET) patients with hepatic metastases (NELM).

PATIENTS AND METHODS

This retrospective analysis included 29 patients with 62 target lesions undergoing everolimus treatment and pre-therapy, and follow-up 68Ga-DOTA-TATE (-TOC) PET/CT scans. Response evaluation utilized progression-free survival (PFS) categorized as responders (R; PFS > 6 months) and non-responders (NR; PFS ≤ 6 months). Lesion size and density, along with maximum and median standardize uptake value (SUV) in target lesions, liver, and spleen were assessed. Tumor-to-spleen (T/S) and tumor-to-liver (T/L) ratios were calculated, including the tumor-to-spleen (T/S) ratio and tumor-to-liver (T/L) ratio (using SUVmax/SUVmax, SUVmax/SUVmean, and SUVmean/SUVmean).

RESULTS

PET/CT scans were acquired 19 days (interquartile range [IQR] 69 days) pre-treatment and 127 days (IQR 74 days) post-starting everolimus. The overall median PFS was 264 days (95% CI: 134-394 days). R exhibited significant decreases in Tmax/Lmax and Tmean/Lmax ratios compared to NR (p = 0.01). In univariate Cox regression, Tmean/Lmax ratio was the sole prognostic parameter associated with PFS (HR 0.5, 95% CI 0.28-0.92, p = 0.03). Percentage changes in T/L and T/S ratios were significant predictors of PFS, with the highest area under curve (AUC) for the percentage change of Tmean/Lmax (AUC = 0.73). An optimal threshold of < 2.5% identified patients with longer PFS (p = 0.003). No other imaging or clinical parameters were predictive of PFS.

CONCLUSIONS

This study highlights the potential of quantitative SSTR-PET/CT in predicting and monitoring everolimus response in NET patients. Liver metastasis-to-liver parenchyma ratios outperformed size-based criteria, and Tmean/Lmax ratio may serve as a prognostic marker for PFS, warranting larger cohort investigation.

Mild autonomous cortisol secretion leads to reduced volumetric BMD at lumbar spine in patients with primary aldosteronism

Objectives

Glucocorticoid cosecretion is more common in primary aldosteronism (PA) than previously thought. Chronic subtle cortisol excess in patients with mild autonomous cortisol secretion (MACS) negatively affects bone health. This study aimed to evaluate the impact of MACS on bone density and turnover markers in PA patients.

Methods

Patients with PA and MACS (n = 50), confirmed by a 1-mg dexamethasone suppression test (DST) with a cortisol cutoff of ≥1.8 µg/dL without symptoms of overt Cushing, were compared to age- and sex-matched patients with PA without MACS (non-MACS, n = 50). Lumbar volumetric bone mineral density (vBMD) was extracted by a novel convolutional neural network (CNN)-based framework (SpineQ software v1.0) applied to routine CT data, incorporated into the diagnostic protocol for PA. Additionally, bone turnover markers-including osteocalcin, bone-specific alkaline phosphatase, N-terminal propeptide of type I collagen, and carboxy-terminal crosslinked telopeptide of type I collagen were evaluated between the groups.

Results

Median cortisol after DST was 1.1 µg/dL (30.3 nmol/L) [IQR: 0.5 µg/dL (13.8 nmol/L)] in the non-MACS group and 2.5 µg/dL (69.0 nmol/L) [IQR: 1.4 µg/dL (38.5 nmol/L)] in the MACS group (p < 0.001). Patients with MACS had significantly lower vBMD values compared to the non-MACS group (106.4 mg/cm³ vs. 116.6 mg/cm³, p = 0.038). Cortisol after DST negatively correlated with vBMD (Spearman's r=-0.33, p=0.00042). No significant differences in bone turnover markers were found, and classifications based on visible lesions on CT or PA-lateralization via adrenal venous sampling did not reveal any significant differences in these markers (p > 0.05 for all comparisons).

Conclusion

Despite non-significant differences in bone turnover markers between patients with PA with or without MACS, CT scans revealed significantly reduced vBMD in PA and MACS patients, indicating compromised bone health and vBMD significantly negatively correlated with cortisol post DST. Thus, opportunistic evaluation of vBMD in routine CT screenings could aid in the early detection of bone alterations in MACS and help mitigate potential long-term adverse effects on bone health.