Altered myocardial substrate metabolism and decreased diastolic function in nonischemic human diabetic cardiomyopathy: studies with cardiac positron emission tomography and magnetic resonance imaging

OBJECTIVES

This study was designed to evaluate myocardial substrate and high-energy phosphate (HEP) metabolism in asymptomatic men with well-controlled, uncomplicated type 2 diabetes with verified absence of cardiac ischemia, and age-matched control subjects, and to assess the association with myocardial function.

BACKGROUND

Metabolic abnormalities, particularly an excessive exposure of the heart to circulating nonesterified fatty acids and myocardial insulin resistance are considered important contributors to diabetic cardiomyopathy in animal models of diabetes. The existence of myocardial metabolic derangements in uncomplicated human type 2 diabetes and their possible contribution to myocardial dysfunction still remain undetermined.

METHODS

In 78 insulin-naive type 2 diabetes men (age 56.5 +/- 5.6 years, body mass index 28.7 +/- 3.5 kg/m(2), glycosylated hemoglobin A(1c) 7.1 +/- 1.0%; expressed as mean +/- SD) without cardiac ischemia and 24 normoglycemic control subjects (age 54.5 +/- 7.1 years, body mass index 27.0 +/- 2.5 kg/m(2), glycosylated hemoglobin A(1c) 5.3 +/- 0.2%), we assessed myocardial left ventricular (LV) function by magnetic resonance imaging, and myocardial perfusion and substrate metabolism by positron emission tomography using H(2)(15)O, carbon (11)C-palmitate, and 18-fluorodeoxyglucose 2-fluoro-2-deoxy-D-glucose. Cardiac HEP metabolism was assessed by phosphorous P 31 magnetic resonance spectroscopy.

RESULTS

In patients, compared with control subjects, LV diastolic function (E/A ratio: 1.04 +/- 0.25 vs. 1.26 +/- 0.36, p = 0.003) and myocardial glucose uptake (260 +/- 128 nmol/ml/min vs. 348 +/- 154 nmol/ml/min, p = 0.015) were decreased, whereas myocardial nonesterified fatty acid uptake (88 +/- 31 nmol/ml/min vs. 68 +/- 18 nmol/ml/min, p = 0.021) and oxidation (85 +/- 30 nmol/ml/min vs. 63 +/- 19 nmol/ml/min, p = 0.007) were increased. There were no differences in myocardial HEP metabolism or perfusion. No association was found between LV diastolic function and cardiac substrate or HEP metabolism.

CONCLUSIONS

Patients versus control subjects showed impaired LV diastolic function and altered myocardial substrate metabolism, but unchanged HEP metabolism. We found no direct relation between cardiac diastolic function and parameters of myocardial metabolism.

Performance evaluation of the ECAT HRRT: an LSO-LYSO double layer high resolution, high sensitivity scanner

The ECAT high resolution research tomograph (HRRT) is a dedicated brain and small animal PET scanner, with design features that enable high image spatial resolution combined with high sensitivity. The HRRT is the first commercially available scanner that utilizes a double layer of LSO/LYSO crystals to achieve photon detection with depth-of-interaction information. In this study, the performance of the commercial LSO/LYSO HRRT was characterized, using the NEMA protocol as a guideline. Besides measurement of spatial resolution, energy resolution, sensitivity, scatter fraction, count rate performance, correction for attenuation and scatter, hot spot recovery and image quality, a clinical evaluation was performed by means of a HR+/HRRT human brain comparison study. Point source resolution varied across the field of view from approximately 2.3 to 3.2 mm (FWHM) in the transaxial direction and from 2.5 to 3.4 mm in the axial direction. Absolute line-source sensitivity ranged from 2.5 to 3.3% and the NEMA-2001 scatter fraction equalled 45%. Maximum NECR was 45 kcps and 148 kcps according to the NEMA-2001 and 1994 protocols, respectively. Attenuation and scatter correction led to a volume uniformity of 6.3% and a system uniformity of 3.1%. Reconstructed values deviated up to 15 and 8% in regions with high and low densities, respectively, which can possibly be assigned to inaccuracies in scatter estimation. Hot spot recovery ranged from 60 to 94% for spheres with diameters of 1 to 2.2 cm. A high quantitative agreement was met between HR+ and HRRT clinical data. In conclusion, the ECAT HRRT has excellent resolution and sensitivity properties, which is a crucial advantage in many research studies.

Pioglitazone improves cardiac function and alters myocardial substrate metabolism without affecting cardiac triglyceride accumulation and high-energy phosphate metabolism in patients with well-controlled type 2 diabetes mellitus

BACKGROUND

Cardiac disease is the leading cause of mortality in type 2 diabetes mellitus (T2DM). Pioglitazone has been associated with improved cardiac outcome but also with an elevated risk of heart failure. We determined the effects of pioglitazone on myocardial function in relation to cardiac high-energy phosphate, glucose, and fatty acid metabolism and triglyceride content in T2DM patients.

METHODS AND RESULTS

Seventy-eight T2DM men without structural heart disease or inducible ischemia as assessed by dobutamine stress echocardiography were assigned to pioglitazone (30 mg/d) or metformin (2000 mg/d) and matching placebo for 24 weeks. The primary end point was change in cardiac diastolic function from baseline relative to myocardial metabolic changes, measured by magnetic resonance imaging, proton and phosphorus magnetic resonance spectroscopy, and [(18)F]-2-fluoro-2-deoxy-D-glucose and [(11)C]palmitate positron emission tomography. No patient developed heart failure. Both therapies similarly improved glycemic control, whole-body insulin sensitivity, and blood pressure. Pioglitazone versus metformin improved the early peak flow rate (P=0.047) and left ventricular compliance. Pioglitazone versus metformin increased myocardial glucose uptake (P<0.001), but pioglitazone-related diastolic improvement was not associated with changes in myocardial substrate metabolism. Metformin did not affect myocardial function but decreased cardiac work relative to pioglitazone (P=0.006), a change that was paralleled by a reduced myocardial glucose uptake and fatty acid oxidation. Neither treatment affected cardiac high-energy phosphate metabolism or triglyceride content. Only pioglitazone reduced hepatic triglyceride content (P<0.001).

CONCLUSIONS

In T2DM patients, pioglitazone was associated with improvement in some measures of left ventricular diastolic function, myocardial glucose uptake, and whole-body insulin sensitivity. The functional changes, however, were not associated with myocardial substrate and high-energy phosphate metabolism.

99mTc-macroaggregated albumin poorly predicts the intrahepatic distribution of 90Y resin microspheres in hepatic radioembolization

In hepatic (90)Y radioembolization, pretreatment (99m)Tc-macroaggregated albumin ((99m)Tc-MAA) nuclear imaging is used for lung shunt analysis, evaluation of extrahepatic deposition, and sometimes for treatment planning, using a partition model. A high level of agreement between pretreatment (99m)Tc-MAA distribution and final (90)Y-microsphere distribution is assumed. The aim of this study was to investigate the value of pretreatment (99m)Tc-MAA SPECT to predict intrahepatic posttreatment (90)Y-microsphere distribution.

METHODS

Volumes of interest (VOIs) were delineated on pretreatment contrast-enhanced CT or MR images according to Couinaud liver segmentation. All VOIs were registered to the (99m)Tc-MAA SPECT and (90)Y SPECT images. The (99m)Tc-MAA SPECT and (90)Y SPECT activity counts were normalized to the total administered activity of (90)Y. For each VOI, this practice resulted in a predictive amount of (90)Y (MBq/cm(3)) based on (99m)Tc-MAA SPECT in comparison with an actual amount of (90)Y based on (90)Y SPECT. Bland-Altman analysis was used to investigate the agreement of the activity distribution between (99m)Tc-MAA SPECT and (90)Y SPECT.

RESULTS

A total of 39 procedures (225 VOIs) in 31 patients were included for analysis. The overall mean difference between pretreatment and posttreatment distribution of activity concentration for all segments was -0.022 MBq/cm(3) with 95% limits of agreement of -0.581 to 0.537 MBq/cm(3) (-28.9 to 26.7 Gy absorbed dose). A difference of >10%, >20%, and >30% of the mean activity per milliliter was found in, respectively, 153 (68%), 97 (43%), and 72 (32%) of the 225 segments. In every (99m)Tc-MAA procedure, at least 1 segment showed an under- or overestimation of >10%. The position of the catheter tip during administrations, as well as the tumor load of the liver segments, significantly influenced the disagreement.

CONCLUSION

In current clinical practice, (99m)Tc-MAA distribution does not accurately predict final (90)Y activity distribution. Awareness of the importance of catheter positioning and adherence to specific recommendations may lead to optimization of individualized treatment planning based on pretreatment imaging.

(⁹⁹m)Tc-MAA overestimates the absorbed dose to the lungs in radioembolization: a quantitative evaluation in patients treated with ¹⁶⁶Ho-microspheres

PURPOSE

Radiation pneumonitis is a rare but serious complication of radioembolic therapy of liver tumours. Estimation of the mean absorbed dose to the lungs based on pretreatment diagnostic (99m)Tc-macroaggregated albumin ((99m)Tc-MAA) imaging should prevent this, with administered activities adjusted accordingly. The accuracy of (99m)Tc-MAA-based lung absorbed dose estimates was evaluated and compared to absorbed dose estimates based on pretreatment diagnostic (166)Ho-microsphere imaging and to the actual lung absorbed doses after (166)Ho radioembolization.

METHODS

This prospective clinical study included 14 patients with chemorefractory, unresectable liver metastases treated with (166)Ho radioembolization. (99m)Tc-MAA-based and (166)Ho-microsphere-based estimation of lung absorbed doses was performed on pretreatment diagnostic planar scintigraphic and SPECT/CT images. The clinical analysis was preceded by an anthropomorphic torso phantom study with simulated lung shunt fractions of 0 to 30 % to determine the accuracy of the image-based lung absorbed dose estimates after (166)Ho radioembolization.

RESULTS

In the phantom study, (166)Ho SPECT/CT-based lung absorbed dose estimates were more accurate (absolute error range 0.1 to -4.4 Gy) than (166)Ho planar scintigraphy-based lung absorbed dose estimates (absolute error range 9.5 to 12.1 Gy). Clinically, the actual median lung absorbed dose was 0.02 Gy (range 0.0 to 0.7 Gy) based on posttreatment (166)Ho-microsphere SPECT/CT imaging. Lung absorbed doses estimated on the basis of pretreatment diagnostic (166)Ho-microsphere SPECT/CT imaging (median 0.02 Gy, range 0.0 to 0.4 Gy) were significantly better predictors of the actual lung absorbed doses than doses estimated on the basis of (166)Ho-microsphere planar scintigraphy (median 10.4 Gy, range 4.0 to 17.3 Gy; p < 0.001), (99m)Tc-MAA SPECT/CT imaging (median 2.5 Gy, range 1.2 to 12.3 Gy; p < 0.001), and (99m)Tc-MAA planar scintigraphy (median 5.5 Gy, range 2.3 to 18.2 Gy; p < 0.001).

CONCLUSION

In clinical practice, lung absorbed doses are significantly overestimated by pretreatment diagnostic (99m)Tc-MAA imaging. Pretreatment diagnostic (166)Ho-microsphere SPECT/CT imaging accurately predicts lung absorbed doses after (166)Ho radioembolization.

Efficient fully 3-D iterative SPECT reconstruction with Monte Carlo-based scatter compensation

Quantitative accuracy of single photon emission computed tomography (SPECT) images is highly dependent on the photon scatter model used for image reconstruction. Monte Carlo simulation (MCS) is the most general method for detailed modeling of scatter, but to date, fully three-dimensional (3-D) MCS-based statistical SPECT reconstruction approaches have not been realized, due to prohibitively long computation times and excessive computer memory requirements. MCS-based reconstruction has previously been restricted to two-dimensional approaches that are vastly inferior to fully 3-D reconstruction. Instead of MCS, scatter calculations based on simplified but less accurate models are sometimes incorporated in fully 3-D SPECT reconstruction algorithms. We developed a computationally efficient fully 3-D MCS-based reconstruction architecture by combining the following methods: 1) a dual matrix ordered subset (DM-OS) reconstruction algorithm to accelerate the reconstruction and avoid massive transition matrix precalculation and storage; 2) a stochastic photon transport calculation in MCS is combined with an analytic detector modeling step to reduce noise in the Monte Carlo (MC)-based reprojection after only a small number of photon histories have been tracked; and 3) the number of photon histories simulated is reduced by an order of magnitude in early iterations, or photon histories calculated in an early iteration are reused. For a 64 x 64 x 64 image array, the reconstruction time required for ten DM-OS iterations is approximately 30 min on a dual processor (AMD 1.4 GHz) PC, in which case the stochastic nature of MCS modeling is found to have a negligible effect on noise in reconstructions. Since MCS can calculate photon transport for any clinically used photon energy and patient attenuation distribution, the proposed methodology is expected to be useful for obtaining highly accurate quantitative SPECT images within clinically acceptable computation times.

Holmium-166 radioembolization for the treatment of patients with liver metastases: design of the phase I HEPAR trial

BACKGROUND

Intra-arterial radioembolization with yttrium-90 microspheres ( 90Y-RE) is an increasingly used therapy for patients with unresectable liver malignancies. Over the last decade, radioactive holmium-166 poly(L-lactic acid) microspheres ( 166Ho-PLLA-MS) have been developed as a possible alternative to 90Y-RE. Next to high-energy beta-radiation, 166Ho also emits gamma-radiation, which allows for imaging by gamma scintigraphy. In addition, Ho is a highly paramagnetic element and can therefore be visualized by MRI. These imaging modalities are useful for assessment of the biodistribution, and allow dosimetry through quantitative analysis of the scintigraphic and MR images. Previous studies have demonstrated the safety of 166Ho-PLLA-MS radioembolization ( 166Ho-RE) in animals. The aim of this phase I trial is to assess the safety and toxicity profile of 166Ho-RE in patients with liver metastases.

METHODS

The HEPAR study (Holmium Embolization Particles for Arterial Radiotherapy) is a non-randomized, open label, safety study. We aim to include 15 to 24 patients with liver metastases of any origin, who have chemotherapy-refractory disease and who are not amenable to surgical resection. Prior to treatment, in addition to the standard technetium-99m labelled macroaggregated albumin ( 99mTc-MAA) dose, a low radioactive safety dose of 60-mg 166Ho-PLLA-MS will be administered. Patients are treated in 4 cohorts of 3-6 patients, according to a standard dose escalation protocol (20 Gy, 40 Gy, 60 Gy, and 80 Gy, respectively). The primary objective will be to establish the maximum tolerated radiation dose of 166Ho-PLLA-MS. Secondary objectives are to assess tumour response, biodistribution, performance status, quality of life, and to compare the 166Ho-PLLA-MS safety dose and the 99mTc-MAA dose distributions with respect to the ability to accurately predict microsphere distribution.

DISCUSSION

This will be the first clinical study on 166Ho-RE. Based on preclinical studies, it is expected that 166Ho-RE has a safety and toxicity profile comparable to that of 90Y-RE. The biochemical and radionuclide characteristics of 166Ho-PLLA-MS that enable accurate dosimetry calculations and biodistribution assessment may however improve the overall safety of the procedure.

The physics of radioembolization

Radioembolization is an established treatment for chemoresistant and unresectable liver cancers. Currently, treatment planning is often based on semi-empirical methods, which yield acceptable toxicity profiles and have enabled the large-scale application in a palliative setting. However, recently, five large randomized controlled trials using resin microspheres failed to demonstrate a significant improvement in either progression-free survival or overall survival in both hepatocellular carcinoma and metastatic colorectal cancer. One reason for this might be that the activity prescription methods used in these studies are suboptimal for many patients.In this review, the current dosimetric methods and their caveats are evaluated. Furthermore, the current state-of-the-art of image-guided dosimetry and advanced radiobiological modeling is reviewed from a physics' perspective. The current literature is explored for the observation of robust dose-response relationships followed by an overview of recent advancements in quantitative image reconstruction in relation to image-guided dosimetry.This review is concluded with a discussion on areas where further research is necessary in order to arrive at a personalized treatment method that provides optimal tumor control and is clinically feasible.

⁹⁰Y Hepatic Radioembolization: An Update on Current Practice and Recent Developments

Radioembolization is an established treatment modality that has been subjected to many improvements over the last decade. Developments are occurring at a high pace, affecting patient selection and treatment. The aim of this review is therefore to provide an overview of current practice, with a focus on recent developments in the field of radioembolization. Several practical issues and recommendations in the application of radioembolization will be discussed, ranging from patient selection to treatment response and future applications.

Quantitative Monte Carlo-based 90Y SPECT reconstruction

The evaluation of radiation absorbed doses in tumorous and healthy tissues is of increasing interest for (90)Y microsphere radioembolization of liver malignancies. The objectives of this work were to introduce and validate a new reconstruction method for quantitative (90)Y bremsstrahlung SPECT to improve posttreatment dosimetry.

METHODS

A fast Monte Carlo simulator was adapted for (90)Y and incorporated into a statistical reconstruction algorithm (SPECT-MC). Photon scatter and attenuation for all photons sampled from the full (90)Y energy spectrum were modeled during reconstruction by Monte Carlo simulations. The energy- and distance-dependent collimator-detector response was modeled with precalculated convolution kernels. The National Electrical Manufacturers Association 2007/International Electrotechnical Commission 2008 image quality phantom was used to quantitatively evaluate the performance of SPECT-MC in comparison with those of state-of-the-art clinical SPECT reconstruction and PET. The liver radiation absorbed doses estimated by SPECT, PET, and SPECT-MC were evaluated in 5 patients consecutively treated with radioembolization.

RESULTS

In comparison with state-of-the-art clinical (90)Y SPECT reconstruction, SPECT-MC substantially improved image contrast (e.g., from 25% to 88% for the 37-mm sphere) and decreased the mean residual count error in the lung insert (from 73% to 15%) at the cost of higher image noise. Image noise and the mean count error were lower for SPECT-MC than for PET. Image contrast was higher in the larger spheres (diameter of ≥28 mm) but lower in the smaller spheres (≤22 mm) for SPECT-MC than for PET. In the clinical study, mean absorbed dose estimates in liver regions with high absorbed doses were consistently higher for SPECT-MC than for SPECT (P = 0.0625) and consistently higher for SPECT-MC than for PET (P = 0.0625).

CONCLUSION

The quantitative accuracy of (90)Y bremsstrahlung SPECT is substantially improved by Monte Carlo-based modeling of the image-degrading factors. Consequently, (90)Y bremsstrahlung SPECT may be used as an alternative to (90)Y PET.

In vivo dosimetry based on SPECT and MR imaging of 166Ho-microspheres for treatment of liver malignancies

(166)Ho-poly(l-lactic acid) microspheres allow for quantitative imaging with MR imaging or SPECT for microsphere biodistribution assessment after radioembolization. The purpose of this study was to evaluate SPECT- and MR imaging-based dosimetry in the first patients treated with (166)Ho radioembolization.

METHODS

Fifteen patients with unresectable, chemorefractory liver metastases of any origin were enrolled in this phase 1 study and were treated with (166)Ho radioembolization according to a dose escalation protocol (20-80 Gy). The contours of all liver segments and all discernible tumors were manually delineated on T2-weighted posttreatment MR images and registered to the posttreatment SPECT images (n = 9) or SPECT/CT images (n = 6) and MR imaging-based R2* maps (n = 14). Dosimetry was based on SPECT (n = 15) and MR imaging (n = 9) for all volumes of interest, tumor-to-nontumor (T/N) activity concentration ratios were calculated, and correlation and agreement of MR imaging- and SPECT-based measurements were evaluated.

RESULTS

The median overall T/N ratio was 1.4 based on SPECT (range, 0.9-2.8) and 1.4 based on MR imaging (range, 1.1-3.1). In 6 of 15 patients (40%), all tumors had received an activity concentration equal to or higher than the normal liver (T/N ratio ≥ 1). Analysis of SPECT and MR imaging measurements for dose to liver segments yielded a high correlation (R(2) = 0.91) and a moderate agreement (mean bias, 3.7 Gy; 95% limits of agreement, -11.2 to 18.7).

CONCLUSION

With the use of (166)Ho-microspheres, in vivo dosimetry is feasible on the basis of both SPECT and MR imaging, which enables personalized treatment by selective targeting of inadequately treated tumors.

The superior predictive value of 166Ho-scout compared with 99mTc-macroaggregated albumin prior to 166Ho-microspheres radioembolization in patients with liver metastases

Purpose

As an alternative to technetium-99m-macroaggregated albumin (^99mTc-MAA), a scout dose of holmium-166 (¹⁶⁶Ho) microspheres can be used prior to ¹⁶⁶Ho-radioembolization. The use of identical particles for pre-treatment and treatment procedures may improve the predictive value of pre-treatment analysis of distribution. The aim of this study was to analyze the agreement between ¹⁶⁶Ho-scout and ¹⁶⁶Ho-therapeutic dose in comparison with the agreement between ^99mTc-MAA and ¹⁶⁶Ho-therapeutic dose.

Methods

Two separate scout dose procedures were performed (^99mTc-MAA and ¹⁶⁶Ho-scout) before treatment in 53 patients. First, qualitative assessment was performed by two blinded nuclear medicine physicians who visually rated the agreement between the ^99mTc-MAA, ¹⁶⁶Ho-scout, and ¹⁶⁶Ho-therapeutic dose SPECT-scans (i.e., all performed in the same patient) on a 5-point scale. Second, agreement was measured quantitatively by delineating lesions and normal liver on FDG-PET/CT. These volumes of interest (VOIs) were co-registered to the SPECT/CT images. The predicted absorbed doses (based on ^99mTc-MAA and ¹⁶⁶Ho-scout) were compared with the actual absorbed dose on post-treatment SPECT.

Results

A total of 23 procedures (71 lesions, 22 patients) were included for analysis. In the qualitative analysis, ¹⁶⁶Ho-scout was superior with a median score of 4 vs. 2.5 for ^99mTc-MAA (p < 0.001). The quantitative analysis showed significantly narrower 95%-limits of agreement for ¹⁶⁶Ho-scout in comparison with ^99mTc-MAA when evaluating lesion absorbed dose (− 90.3 and 105.3 Gy vs. − 164.1 and 197.0 Gy, respectively). Evaluation of normal liver absorbed dose did not show difference in agreement between both scout doses and ¹⁶⁶Ho-therapeutic dose (− 2.9 and 5.5 Gy vs − 3.6 and 4.1 Gy for ^99mTc-MAA and ¹⁶⁶Ho-scout, respectively).

Conclusions

In this study, ¹⁶⁶Ho-scout was shown to have a superior predictive value for intrahepatic distribution in comparison with ^99mTc-MAA.

MRI-based biodistribution assessment of holmium-166 poly(L-lactic acid) microspheres after radioembolisation

Objectives

To demonstrate the feasibility of MRI-based assessment of the intrahepatic Ho-PLLA-MS biodistribution after radioembolisation in order to estimate the absorbed radiation dose.

Methods

Fifteen patients were treated with holmium-166 (¹⁶⁶Ho) poly(L-lactic acid)-loaded microspheres (Ho-PLLA-MS, mean 484 mg; range 408–593 mg) in a phase I study. Multi-echo gradient-echo MR images were acquired from which R₂^* maps were constructed. The amount of Ho-PLLA-MS in the liver was determined by using the relaxivity r₂^* of the Ho-PLLA-MS and compared with the administered amount. Quantitative single photon emission computed tomography (SPECT) was used for comparison with MRI regarding the whole liver absorbed radiation dose.

Results

R₂^* maps visualised the deposition of Ho-PLLA-MS with great detail. The mean total amount of Ho-PLLA-MS detected in the liver based on MRI was 431 mg (range 236–666 mg) or 89 ± 19 % of the delivered amount (correlation coefficient r = 0.7; P < 0.01). A good correlation was found between the whole liver mean absorbed radiation dose as assessed by MRI and SPECT (correlation coefficient r = 0.927; P < 0.001).

Conclusion

MRI-based dosimetry for holmium-166 radioembolisation is feasible. Biodistribution is visualised with great detail and quantitative measurements are possible.

Key Points

• Radioembolisation is increasingly used for treating unresectable primary or metastatic liver tumours.

• MRI-based intrahepatic microsphere biodistribution assessment is feasible after holmium-166 radioembolisation.

• MRI enables quantification of holmium-166 microspheres in liver in a short imaging time.

• MRI can estimate the whole liver absorbed radiation dose following holmium-166 radioembolisation.

Clinical and Imaging Predictors of Recurrent Ischemic Stroke: A Systematic Review and Meta-Analysis

BACKGROUND

Predictors of recurrent ischemic stroke are less well known in patients with a recent ischemic stroke than in patients with transient ischemic attack (TIA). We identified clinical and radiological factors for predicting recurrent ischemic stroke in patients with recent ischemic stroke.

METHODS

A systematic search in PubMed, Embase, Cochrane Library, and CINAHL was performed with the terms "ischemic stroke," "predictors/determinants," and "recurrence." Quality assessment of the articles was performed and the level of evidence was graded for the articles included for the meta-analysis. Pooled risk ratios (RR) and heterogeneity (I2) were calculated using inverse variance random effects models.

RESULTS

Ten articles with high-quality results were identified for meta-analysis. Past medical history of stroke or TIA was a predictor of recurrent ischemic stroke (pooled RR 2.5, 95% CI 2.1-3.1). Small vessel strokes were associated with a lower risk of recurrence than large vessel strokes (pooled RR 0.3, 95% CI 0.1-0.7). Patients with stroke of an undetermined cause had a lower risk of recurrence than patients with large artery atherosclerosis (pooled RR 0.5, 95% CI 0.2-1.1). We found no studies using CT or ultrasound for the prediction of recurrent ischemic stroke. The following MRI findings were predictors of recurrent ischemic stroke: multiple lesions (pooled RR 1.7, 95% CI 1.5-2.0), multiple stage lesions (pooled RR 4.1, 95% CI 3.1-5.5), multiple territory lesions (pooled RR 2.9, 95% CI 2.0-4.2), chronic infarcts (pooled RR 1.5, 95% CI 1.2-1.9), and isolated cortical lesions (pooled RR 2.2, 95% CI 1.5-3.2).

CONCLUSIONS

In patients with a recent ischemic stroke, a history of stroke or TIA and the subtype large artery atherosclerosis are associated with an increased risk of recurrent ischemic stroke. Predictors evaluated with MRI include multiple ischemic changes and isolated cortical lesions. Predictors of recurrent ischemic stroke concerning CT or ultrasound have not been published.

Quantitative Monte Carlo-based holmium-166 SPECT reconstruction

PURPOSE

Quantitative imaging of the radionuclide distribution is of increasing interest for microsphere radioembolization (RE) of liver malignancies, to aid treatment planning and dosimetry. For this purpose, holmium-166 ((166)Ho) microspheres have been developed, which can be visualized with a gamma camera. The objective of this work is to develop and evaluate a new reconstruction method for quantitative (166)Ho SPECT, including Monte Carlo-based modeling of photon contributions from the full energy spectrum.

METHODS

A fast Monte Carlo (MC) simulator was developed for simulation of (166)Ho projection images and incorporated in a statistical reconstruction algorithm (SPECT-fMC). Photon scatter and attenuation for all photons sampled from the full (166)Ho energy spectrum were modeled during reconstruction by Monte Carlo simulations. The energy- and distance-dependent collimator-detector response was modeled using precalculated convolution kernels. Phantom experiments were performed to quantitatively evaluate image contrast, image noise, count errors, and activity recovery coefficients (ARCs) of SPECT-fMC in comparison with those of an energy window-based method for correction of down-scattered high-energy photons (SPECT-DSW) and a previously presented hybrid method that combines MC simulation of photopeak scatter with energy window-based estimation of down-scattered high-energy contributions (SPECT-ppMC+DSW). Additionally, the impact of SPECT-fMC on whole-body recovered activities (A(est)) and estimated radiation absorbed doses was evaluated using clinical SPECT data of six (166)Ho RE patients.

RESULTS

At the same noise level, SPECT-fMC images showed substantially higher contrast than SPECT-DSW and SPECT-ppMC+DSW in spheres ≥ 17 mm in diameter. The count error was reduced from 29% (SPECT-DSW) and 25% (SPECT-ppMC+DSW) to 12% (SPECT-fMC). ARCs in five spherical volumes of 1.96-106.21 ml were improved from 32%-63% (SPECT-DSW) and 50%-80% (SPECT-ppMC+DSW) to 76%-103% (SPECT-fMC). Furthermore, SPECT-fMC recovered whole-body activities were most accurate (A(est) = 1.06 × A - 5.90 MBq, R(2) = 0.97) and SPECT-fMC tumor absorbed doses were significantly higher than with SPECT-DSW (p = 0.031) and SPECT-ppMC+DSW (p = 0.031).

CONCLUSIONS

The quantitative accuracy of (166)Ho SPECT is improved by Monte Carlo-based modeling of the image degrading factors. Consequently, the proposed reconstruction method enables accurate estimation of the radiation absorbed dose in clinical practice.

Additional holmium-166 radioembolisation after lutetium-177-dotatate in patients with neuroendocrine tumour liver metastases (HEPAR PLuS): a single-centre, single-arm, open-label, phase 2 study

BACKGROUND

In patients with metastatic neuroendocrine neoplasms, the liver is the most commonly affected organ and a crucial factor for prognosis and survival. Peptide receptor radionuclide therapy can prolong progression-free survival in these patients. Additional treatment of liver disease might further improve outcomes. We aimed to investigate the safety and efficacy of additional holmium-166 (¹⁶⁶Ho) radioembolisation after peptide receptor radionuclide therapy in patients with metastatic liver neuroendocrine neoplasms.

METHODS

The Holmium Embolization Particles for Arterial Radiotherapy Plus ¹⁷⁷Lu-Dotatate in Salvage Neuroendocrine Tumour Patients (HEPAR PLuS) study was a single-centre, phase 2 study done at the University Medical Center Utrecht (Utrecht, Netherlands). Patients, aged at least 18 years, with histologically proven grade 1 or 2 neuroendocrine neoplasms of all origins, an Eastern Cooperative Oncology Group performance status of 0-2, and three or more measurable liver metastases according to Response Evaluation Criteria In Solid Tumors (RECIST) version 1.1 criteria received ¹⁶⁶Ho-radioembolisation within 20 weeks after four cycles of peptide receptor radionuclide therapy (lutetium-177-dotatate [¹⁷⁷Lu-dotatate]). The primary endpoint was objective liver tumour response in the treated liver volume, defined as complete response (disappearance of all lesions) or partial response (≥30% decrease in the sum of the longest diameters of the target lesions, compared with baseline measurements), according to RECIST 1.1, analysed per protocol at 3 months. Safety was assessed in all patients who received treatment. This study is registered with ClinicalTrials.gov, NCT02067988. Recruitment is completed and long-term follow-up is ongoing.

FINDINGS

From Oct 15, 2014, to Sept 12, 2018, 34 patients were assessed for eligibility. 31 patients received treatment and 30 (97%) patients were available for primary endpoint assessment and completed 6 months of follow-up. Three (9%) patients were excluded at screening and one (3%) patient was treated and died before the primary endpoint and was replaced. According to the per-protocol analysis 13 (43%; 95% CI 26-63) of 30 patients achieved an objective response in the treated volume. The most frequently reported Common Terminology Criteria for Adverse Events (CTCAE) grade 3-4 clinical and laboratory toxicities within 6 months included abdominal pain (three [10%] of 31 patients), increased γ-glutamyl transpeptidase (16 [54%]), and lymphocytopenia (seven [23%]). One (3%) fatal treatment-related serious adverse event occurred (radioembolisation-induced liver disease). Two (6%) patients had serious adverse events deemed to be unrelated to treatment (gastric ulcer and perforated cholecystitis).

INTERPRETATION

¹⁶⁶Ho-radioembolisation, as an adjunct to peptide receptor radionuclide therapy in patients with neuroendocrine neoplasm liver metastases, is safe and efficacious. Radioembolisation can be considered in patients with bulky liver disease, including after peptide receptor radionuclide therapy. A future randomised, controlled study should investigate the added benefit of this treatment on progression-free survival.

FUNDING

None.

Monte Carlo simulations of pinhole imaging accelerated by kernel-based forced detection

Pinhole collimation can provide both higher sensitivity and resolution than parallel hole collimation when used to image small objects. When objects are placed close to the pinhole, small pinhole diameters combined with high-magnification pinhole geometries yield ultra high resolution images. With Monte Carlo (MC) calculations it is possible to simulate accurately a wide range of features of pinhole imaging. The aim of the present work is to accelerate MC simulations of pinhole SPECT projections. To achieve speed-up, forced detection (FD), a commonly used acceleration technique, is replaced by a kernel-based forced detection (KFD) step. In KFD, instead of tracing individual photons from the source or last scatter position to the detector, a position dependent kernel (point spread function (PSF)) is projected on the detector. The PSFs for channel and knife edge pinhole apertures model the penetration effects through the aperture material. For simulations, the PSFs are pre-calculated and stored in tables. The speed-up and accuracy achieved by using KFD were validated by means of digital phantoms. MC simulations with FD and with KFD converge to almost identical images. However, KFD converges to an equal image noise level one to four orders of magnitude faster than FD, depending on the number of photons simulated. A simulator accelerated by KFD could serve as a practical tool to improve iterative image reconstruction.

Variability in lutetium-177 SPECT quantification between different state-of-the-art SPECT/CT systems

BACKGROUND

Quantitative SPECT imaging in targeted radionuclide therapy with lutetium-177 holds great potential for individualized treatment based on dose assessment. The establishment of dose-effect relations requires a standardized method for SPECT quantification. The purpose of this multi-center study is to evaluate quantitative accuracy and inter-system variations of different SPECT/CT systems with corresponding commercially available quantitative reconstruction algorithms. This is an important step towards a vendor-independent standard for quantitative lutetium-177 SPECT.

METHODS

Four state-of-the-art SPECT/CT systems were included: Discovery™ NM/CT 670Pro (GE Healthcare), Symbia Intevo™, and two Symbia™ T16 (Siemens Healthineers). Quantitative accuracy and inter-system variations were evaluated by repeatedly scanning a cylindrical phantom with 6 spherical inserts (0.5 - 113 ml). A sphere-to-background activity concentration ratio of 10:1 was used. Acquisition settings were standardized: medium energy collimator, body contour trajectory, photon energy window of 208 keV (± 10%), adjacent 20% lower scatter window, 2 × 64 projections, 128 × 128 matrix size, and 40 s projection time. Reconstructions were performed using GE Evolution with Q.Metrix™, Siemens xSPECT Quant™, Siemens Broad Quantification™ or Siemens Flash3D™ algorithms using vendor recommended settings. In addition, projection data were reconstructed using Hermes SUV SPECT™ with standardized reconstruction settings to obtain a vendor-neutral quantitative reconstruction for all systems. Volumes of interest (VOI) for the spheres were obtained by applying a 50% threshold of the sphere maximum voxel value corrected for background activity. For each sphere, the mean and maximum recovery coefficient (RC_mean and RC_max) of three repeated measurements was calculated, defined as the imaged activity concentration divided by the actual activity concentration. Inter-system variations were defined as the range of RC over all systems.

RESULTS

RC decreased with decreasing sphere volume. Inter-system variations with vendor-specific reconstructions were between 0.06 and 0.41 for RC_mean depending on sphere size (maximum 118% quantification difference), and improved to 0.02-0.19 with vendor-neutral reconstructions (maximum 38% quantification difference).

CONCLUSION

This study shows that eliminating sources of possible variation drastically reduces inter-system variation in quantification. This means that absolute SPECT quantification for ¹⁷⁷Lu is feasible in a multi-center and multi-vendor setting; however, close agreement between vendors and sites is key for multi-center dosimetry and quantitative biomarker studies.

Dose-Effect Relationships of 166Ho Radioembolization in Colorectal Cancer

Radioembolization is a treatment option for colorectal cancer (CRC) patients with inoperable, chemorefractory hepatic metastases. Personalized treatment requires established dose thresholds. Hence, the aim of this study was to explore the relationship between dose and effect (i.e., response and toxicity) in CRC patients treated with ¹⁶⁶Ho radioembolization. Methods: CRC patients treated in the HEPAR II and SIM studies were analyzed. Absorbed doses were estimated using the activity distribution on posttreatment ¹⁶⁶Ho SPECT/CT. Metabolic response was assessed using the change in total-lesion glycolysis on ¹⁸F-FDG PET/CT between baseline and 3-mo follow-up. Toxicity between treatment and 3 mo was evaluated according to the Common Terminology Criteria for Adverse Events (CTCAE), version 5, and its relationship with parenchyma-absorbed dose was assessed using linear models. The relationship between tumor-absorbed dose and patient- and tumor-level response was analyzed using linear mixed models. Using a threshold of 100% sensitivity for response, the threshold for a minimal mean tumor-absorbed dose was determined and its impact on survival was assessed. Results: Forty patients were included. The median parenchyma-absorbed dose was 37 Gy (range, 12-55 Gy). New CTCAE grade 3 or higher clinical and laboratory toxicity was present in 8 and 7 patients, respectively. For any clinical toxicity (highest grade per patient), the mean difference in parenchymal dose (Gy) per step increase in CTCAE grade category was 5.75 (95% CI, 1.18-10.32). On a patient level, metabolic response was as follows: complete response, n = 1; partial response, n = 11; stable disease, n = 17; and progressive disease, n = 8. The mean tumor-absorbed dose was 84% higher in patients with complete or partial response than in patients with progressive disease (95% CI, 20%-180%). Survival for patients with a mean tumor-absorbed dose of more than 90 Gy was significantly better than for patients with a mean tumor-absorbed dose of less than 90 Gy (hazard ratio, 0.16; 95% CI, 0.06-0.511). Conclusion: A significant dose-response relationship in CRC patients treated with ¹⁶⁶Ho radioembolization was established, and a positive association between toxicity and parenchymal dose was found. For future patients, it is advocated to use a ¹⁶⁶Ho scout dose to select patients and yo personalize the administered activity, targeting a mean tumor-absorbed dose of more than 90 Gy and a parenchymal dose of less than 55 Gy.

Safety of a Scout Dose Preceding Hepatic Radioembolization with 166Ho Microspheres

Before (166)Ho radioembolization, a small batch of the same type of microspheres is administered as a scout dose instead of the conventional (99m)Tc-macroaggregated albumin ((99m)Tc-MAA). The (166)Ho scout dose provides a more accurate and precise lung shunt assessment. However, in contrast to (99m)Tc-MAA, an unintended extrahepatic deposition of this β-emitting scout dose could inflict radiation damage, the extent of which we aimed to quantify in this study.

METHODS

All patients eligible for radioembolization in our institute between January 2011 and March 2014 were reviewed. Of the extrahepatic depositions of (99m)Tc-MAA on SPECT, the amount and volume were measured. These were used to calculate the theoretic absorbed dose in the case a (166)Ho scout dose had been used. The extrahepatic activity was measured as the sum of all voxels of the deposition. Volumes were measured using a threshold technique including all voxels from the maximum voxel intensity up to a certain percentage. The threshold needed to obtain the true volume was studied in a phantom study.

RESULTS

In the phantom study, a threshold of 40% was found to overestimate the volume, with the consequence of underestimating the absorbed dose. Of 160 patients, 32 patients (34 cases) of extrahepatic deposition were identified. The depositions contained a median of 1.3% (range, 0.1%-19.5%) of the administered activity in a median volume of 6.8 mL (range, 1.1-42 mL). The use of a scout dose of 250 MBq of (166)Ho microspheres in these cases would theoretically have resulted in a median absorbed dose of 6.0 Gy (range, 0.9-374 Gy). The dose exceeded a limit of 49 Gy (reported in 2013) in 2 of 34 cases (5.9%; 95% confidence interval, 0.7%-20.1%) or 2 of 160 (1.3%; 95% confidence interval, 0.1%-4.7%) of all patients. In these 2 patients with a large absorbed dose (112 and 374 Gy), the culprit vessel was identified in 1 case.

CONCLUSION

Extrahepatic deposition of a (166)Ho scout dose seems to be theoretically safe in most patients. Its safety in clinical practice is being evaluated in ongoing clinical trials.

Additional hepatic 166Ho-radioembolization in patients with neuroendocrine tumours treated with 177Lu-DOTATATE; a single center, interventional, non-randomized, non-comparative, open label, phase II study (HEPAR PLUS trial)

Background

Neuroendocrine tumours (NET) consist of a heterogeneous group of neoplasms with various organs of origin. At diagnosis 21% of the patients with a Grade 1 NET and 30% with a Grade 2 NET have distant metastases. Treatment with peptide receptor radionuclide therapy (PRRT) shows a high objective response rate and long median survival after treatment. However, complete remission is almost never achieved. The liver is the most commonly affected organ in metastatic disease and is the most incriminating factor for patient survival. Additional treatment of liver disease after PRRT may improve outcome in NET patients. Radioembolization is an established therapy for liver metastasis. To investigate this hypothesis, a phase 2 study was initiated to assess effectiveness and toxicity of holmium-166 radioembolization (¹⁶⁶Ho-RE) after PRRT with lutetium-177 (¹⁷⁷Lu)-DOTATATE.

Methods

The HEPAR PLUS trial (“HolmiumEmbolizationParticles forArterialRadiotherapyPlus¹⁷⁷Lu-DOTATATE inSalvage NET patients”) is a single centre, interventional, non-randomized, non-comparative, open label study. In this phase 2 study 30–48 patients with > 3 measurable liver metastases according to RECIST 1.1 will receive additional ¹⁶⁶Ho-RE within 20 weeks after the 4th and last cycle of PRRT with 7.4 GBq ¹⁷⁷Lu-DOTATATE. Primary objectives are to assess tumour response, complete and partial response according to RECIST 1.1, and toxicity, based on CTCAE v4.03, 3 months after ¹⁶⁶Ho-RE. Secondary endpoints include biochemical response, quality of life, biodistribution and dosimetry.

Discussion

This is the first prospective study to combine PRRT with ¹⁷⁷Lu-DOTATATE and additional ¹⁶⁶Ho-RE in metastatic NET. A radiation boost on intrahepatic disease using ¹⁶⁶Ho-RE may lead to an improved response rate without significant additional side-effects.

Trial registration

Clinicaltrials.gov NCT02067988, 13 February 2014. Protocol version: 6, 30 november 2016.

Holmium-166 Radioembolization: Current Status and Future Prospective

Since its first suggestion as possible option for liver radioembolization treatment, the therapeutic isotope holmium-166 (¹⁶⁶Ho) caught the experts’ attention due to its imaging possibilities. Being not only a beta, but also a gamma emitter and a lanthanide, ¹⁶⁶Ho can be imaged using single-photon emission computed tomography and magnetic resonance imaging, respectively. Another advantage of ¹⁶⁶Ho is the possibility to perform the scout and treatment procedure with the same particle. This prospect paves the way to an individualized treatment procedure, gaining more control over dosimetry-based patient selection and treatment planning. In this review, an overview on ¹⁶⁶Ho liver radioembolization will be presented. The current clinical workflow, together with the most relevant clinical findings and the future prospective will be provided.

Accelerated SPECT image reconstruction with FBP and an image enhancement convolutional neural network

BACKGROUND

Monte Carlo-based iterative reconstruction to correct for photon scatter and collimator effects has been proven to be superior over analytical correction schemes in single-photon emission computed tomography (SPECT/CT), but it is currently not commonly used in daily clinical practice due to the long associated reconstruction times. We propose to use a convolutional neural network (CNN) to upgrade fast filtered back projection (FBP) image quality so that reconstructions comparable in quality to the Monte Carlo-based reconstruction can be obtained within seconds.

RESULTS

A total of 128 technetium-99m macroaggregated albumin pre-treatment SPECT/CT scans used to guide hepatic radioembolization were available. Four reconstruction methods were compared: FBP, clinical reconstruction, Monte Carlo-based reconstruction, and the neural network approach. The CNN generated reconstructions in 5 sec, whereas clinical reconstruction took 5 min and the Monte Carlo-based reconstruction took 19 min. The mean squared error of the neural network approach in the validation set was between that of the Monte Carlo-based and clinical reconstruction, and the lung shunting fraction difference was lower than 2 percent point. A phantom experiment showed that quantitative measures required in radioembolization were accurately retrieved from the CNN-generated reconstructions.

CONCLUSIONS

FBP with an image enhancement neural network provides SPECT reconstructions with quality close to that obtained with Monte Carlo-based reconstruction within seconds.