Urinary excretion kinetics of [¹⁷⁷Lu]Lu-PSMA-617

Introduction: For the implementation of suitable radiation safety measures in [177Lu]Lu-PSMA-617 therapy, additional insight into excretion kinetics is important. This study evaluates this kinetics in prostate cancer patients via direct urine measurements. Methods: Both the short-term (up to 24 h, n = 28 cycles) and long-term kinetics (up to 7 weeks, n = 35 samples) were evaluated by collection of urine samples. Samples were measured on a scintillation counter to determine excretion kinetics. Results: The mean excretion half-time during the first 20 h was 4.9 h. Kinetics was significantly different for patients with kidney function below or above eGFR 65 ml/min. Calculated skin equivalent dose in case of urinary contamination was between 50 and 145 mSv when it was caused between 0 and 8 h p.i. Measurable amounts of 177Lu were found in urine samples up to 18 days p.i. Conclusion: Excretion kinetics of [177Lu]Lu-PSMA-617 is especially relevant during the first 24 h, when accurate radiation safety measures are important to prevent skin contamination. Measures for accurate waste management are relevant up to 18 days.</p

A 3D-printed anatomical pancreas and kidney phantom for optimizing SPECT/CT reconstruction settings in beta cell imaging using 111In-exendin

Contains fulltext : 165641.pdf (publisher's version ) (Open Access)BACKGROUND: Quantitative single photon emission computed tomography (SPECT) is challenging, especially for pancreatic beta cell imaging with 111In-exendin due to high uptake in the kidneys versus much lower uptake in the nearby pancreas. Therefore, we designed a three-dimensionally (3D) printed phantom representing the pancreas and kidneys to mimic the human situation in beta cell imaging. The phantom was used to assess the effect of different reconstruction settings on the quantification of the pancreas uptake for two different, commercially available software packages. METHODS: 3D-printed, hollow pancreas and kidney compartments were inserted into the National Electrical Manufacturers Association (NEMA) NU2 image quality phantom casing. These organs and the background compartment were filled with activities simulating relatively high and low pancreatic 111In-exendin uptake for, respectively, healthy humans and type 1 diabetes patients. Images were reconstructed using Siemens Flash 3D and Hermes Hybrid Recon, with varying numbers of iterations and subsets and corrections. Images were visually assessed on homogeneity and artefacts, and quantitatively by the pancreas-to-kidney activity concentration ratio. RESULTS: Phantom images were similar to clinical images and showed comparable artefacts. All corrections were required to clearly visualize the pancreas. Increased numbers of subsets and iterations improved the quantitative performance but decreased homogeneity both in the pancreas and the background. Based on the phantom analyses, the Hybrid Recon reconstruction with 6 iterations and 16 subsets was found to be most suitable for clinical use. CONCLUSIONS: This work strongly contributed to quantification of pancreatic 111In-exendin uptake. It showed how clinical images of 111In-exendin can be interpreted and enabled selection of the most appropriate protocol for clinical use

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 (RCmean and RCmax) 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. Re

Amplitude-based optimal respiratory gating in positron emission tomography in patients with primary lung cancer

Objectives Respiratory motion during PET imaging introduces quantitative and diagnostic inaccuracies, which may result in non-optimal patient management. This study investigated the effects of respiratory gating on image quantification using an amplitude-based optimal respiratory gating (ORG) algorithm. Methods Whole body FDG-PET/CT was performed in 66 lung cancer patients. The respiratory signal was obtained using a pressure sensor integrated in an elastic belt placed around the patient’s thorax. ORG images were reconstructed with 50 %, 35 %, and 20 % of acquired PET data (duty cycle). Lesions were grouped into anatomical locations. Differences in lesion volume between ORG and non-gated images, and mean FDG-uptake (SUVmean) were calculated. Results Lesions in the middle and lower lobes demonstrated a significant SUVmean increase for all duty cycles and volume decrease for duty cycles of 35 % and 20 %. Significant increase in SUVmean and decrease in volume for lesions in the upper lobes were observed for a 20 % duty cycle. The SUVmean increase for central lesions was significant for all duty cycles, whereas a significant volume decrease was observed for a duty cycle of 20 %. Conclusions This study implies that ORG could influence clinical PET imaging with respect to response monitoring and radiotherapy planning

Metal artifact reduction of CT scans to improve PET/CT

In recent years, different metal artifact reduction methods have been developed for CT. These methods have only recently been introduced for PET/CT even though they could be beneficial for interpretation, segmentation, and quantification of the PET/CT images. In this study, phantom and patient scans were analyzed visually and quantitatively to measure the effect on PET images of iterative metal artifact reduction (iMAR) of CT data. Methods: The phantom consisted of 2 types of hip prostheses in a solution of 18F-FDG and water. 18F-FDG PET/CT scans of 14 patients with metal implants (either dental implants, hip prostheses, shoulder prostheses, or pedicle screws) and 68Ga-labeled prostate-specific membrane antigen (68Ga-PSMA) PET/CT scans of 7 patients with hip prostheses were scored by 2 experienced nuclear medicine physicians to analyze clinical relevance. For all patients, a lesion was located in the field of view of the metal implant. Phantom and patients were scanned in a PET/CT scanner. The standard low-dose CT scans were processed with the iMAR algorithm. The PET data were reconstructed using attenuation correction provided by both standard CT and iMAR-processed CT. Results: For the phantom scans, cold artifacts were visible on the PET image. There was a 30% deficit in 18F-FDG concentration, which was restored by iMAR processing, indicating that metal artifacts on CT images induce quantification errors in PET data. The iMAR algorithm was useful for most patients. When iMAR was used, the confidence in interpretation increased or stayed the same, with an average improvement of 28% 6 20% (scored on a scale of 0%–100% confidence). The SUV increase or decrease depended on the type of metal artifact. The mean difference in absolute values of SUVmean of the lesions was 3.5% 6 3.3%. Conclusion: The iMAR algorithm increases the confidence of the interpretation of the PET/CT scan and influences the SUV. The added value of iMAR depends on the indication for the PET/CT scan, location and size/type of the prosthesis, and location and extent of the disease

Comparison of a Free-Breathing CT and an Expiratory Breath-Hold CT with Regard to Spatial Alignment of Amplitude-Based Respiratory-Gated PET and CT Images

Respiratory motion during PET has a significant effect on the quantification of radiotracer uptake in PET images. Even when respiratory motion is considered using PET gating techniques, inaccuracies in standardized uptake values can be caused by inappropriate attenuation correction due to a spatial mismatch between PET and CT. In this study, the effect of breath-hold CT imaging on the spatial match between CT and amplitude-based respiratory-gated PET images is investigated.Whole-body (18)F-FDG PET/CT imaging was performed in 52 patients with 125 lung lesions. (18)F-FDG PET was performed using optimized, amplitude-based respiratory gating. For CT, 36 patients were randomly assigned to the free-breathing (FB) group and 16 to the rest-expiratory breath-hold (BH) group. Spatial mismatch between the PET and CT images was quantified by measuring the distance between the centroids of PET and CT lesions and calculating the Jaccard similarity coefficient (JSC).In the upper lobes, the average distance between the centroids of the PET and CT lesions was 4.7 ± 3.1 and 6.0 ± 3.0 mm for the FB and BH groups, respectively (P = 0.11). For the middle and lower lobes, the distances were 5.8 ± 4.3 and 5.1 ± 2.9 mm (P = 0.70), respectively, and for the central region 4.8 ± 4.6 and 5.6 ± 2.0 mm (P = 0.24), respectively. The JSC for the upper lobes was 0.28 ± 0.17 and 0.28 ± 0.19, for the FB and the BH group, respectively (P = 0.83). For the middle and lower lobes, the JSC was 0.22 ± 0.16 and 0.28 ± 0.18 (P = 0.20), respectively, and for the central region 0.39 ± 0.17 and 0.13 ± 0.04 (P = 0.04), respectively.Providing breathing instructions to the patients during the CT acquisition did not improve the spatial alignment between the respiratory-gated PET images and the CT images. The difficulty experienced in using this clinical protocol, such as patient compliance and operator dependence, emphasizes the need for other strategies

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

Following publication of the original article [1], it was reported that the sphere volumes defined in the original article should be adjusted. The correct inner diameters (and volumes) of the spherical inserts were: 9.9mm (0.5 ml), 15.4mm (2.0 ml), 19.8 mm (4.0 ml), 24.8mm (8.0 ml), 31.3mm (16.0 ml) and 60mm (113 ml). Figures 3, 5 and 6 have been adjusted accordingly. The original article has been updated.</p