EJNMMI Physics最新文献

Background: Prior studies have established that macroaggregated albumin (MAA)-SPECT/CT offers more robust lung shunt fraction (LSF) and lung mean absorbed dose (LMD) estimates in ⁹⁰Y radioembolization in comparison to planar imaging. However, incomplete SPECT/CT coverage of the lungs is common due to clinical workflows, complicating its potential use for LSF and LMD calculations. In this work, lung truncation in MAA-SPECT/CT was addressed via correction strategies to improve ⁹⁰Y treatment planning.

Methods: Lung truncation was simulated in 56 cases with adequate (> 90%, mean: 98%) lung coverage in MAA-SPECT/CT by removing slices in ~ 5 mm increments from the lung apices to the diaphragm. A wide range of lung coverages from 100% to < 1% in ~ 2% increments were created. LSF and LMD were calculated with four methods. (1) 2D planar imaging standard (not truncated), truncated lung SPECT/CT data was: (2) used with no corrections (SPECT_Trunc), (3) uniformly extrapolated to full lung coverage (SPECT_Uniform), (4) fit with an empirical model to predict lung counts at full lung coverage (SPECT_Fit). To determine counts for LSF, full lung volumes, those modified at the lung/liver boundary (Lungs 2-cm), and those isolated to the left lung (Left Lung) were used. The correction methods were then applied to 31 independent cases without full lung coverage (< 90%, mean: 74%). The variations in LSF and LMD estimates from each correction method were analyzed.

Results: Averaged across simulated lung coverages from 40 to 80%, percent errors relative to non-truncated data for SPECT_Trunc were (mean ± σ) - 22% ± 15% for LSF and 34% ± 29% for LMD. SPECT_Uniform had similar errors with 29% ± 26% for both LSF and LMD. SPECT_Fit yielded the most accurate and precise estimates for LSF and LMD, with errors of 11% ± 20% for both. The Left Lung approach equalized LMD errors in all three correction methods, with percent errors of 3% ± 17% (SPECT_Trunc), 2% ± 17% (SPECT_Uniform), and 4% ± 13% (SPECT_Fit). In the 31 cases without ground truth LSF or LMD, Left Lung produced highly comparable LMD estimates, with a mean (max) coefficient of variation across the three correction methods of 4% (20%).

Conclusion: LSF and LMD can be estimated for ⁹⁰Y radioembolization using truncated lung coverage data in MAA-SPECT/CT. Empirical models to predict lung counts at full lung coverage produced LSF and LMD estimates with minimal bias and uncertainty. With lung/liver boundary adjustments, all SPECT/CT methods assessed in this work yielded LMD estimates comparable to ground truth, even down to 50% lung coverage.

Purpose: This study aimed to implement high-end positron emission tomography (PET) equipment to assist conventional PET equipment in improving image quality via a distribution learning-based diffusion model.

Methods: A diffusion model was first trained on a dataset of high-quality (HQ) images acquired by a high-end PET device (uEXPLORER scanner), and the quality of the conventional PET images was later improved on the basis of this trained model built on null-space constraints. Data from 180 patients were used in this study. Among them, 137 patients who underwent total-body PET/computed tomography scans via a uEXPLORER scanner at the Sun Yat-sen University Cancer Center were retrospectively enrolled. The datasets of 50 of these patients were used to train the diffusion model. The remaining 87 cases and 43 PET images acquired from The Cancer Imaging Archive were used to quantitatively and qualitatively evaluate the proposed method. The nonlocal means (NLM) method, UNet and a generative adversarial network (GAN) were used as reference methods.

Results: The incorporation of HQ imaging priors derived from high-end devices into the diffusion model through network training can enable the sharing of information between scanners, thereby pushing the limits of conventional scanners and improving their imaging quality. The quantitative results showed that the diffusion model based on null-space constraints produced better and more stable results than those of the methods based on NLM, UNet and the GAN and is well suited for cross-center and cross-device imaging.

Conclusion: A diffusion model based on null-space constraints is a flexible framework that can effectively utilize the prior information provided by high-end scanners to improve the image quality of conventional scanners in cross-center and cross-device scenarios.

Purpose: Clinical trials have yielded promising results for ¹⁷⁷Lutetium Prostate Specific Membrane Antigen (¹⁷⁷Lu-PSMA) therapy in metastatic castration resistant prostate cancer (mCRPC) patients. However, the development of precise methods for internal dosimetry and accurate dose estimation has been considered ongoing research. This study aimed to calculate the absorbed dose to the critical organs and metastasis regions using GATE 9.0 Monte Carlo simulation (MCS) as a gold standard to compare the OLINDA 1.1 and IDAC 2.1 software.

Material and methods: This study investigated absorbed doses to different organs in 9 mCRPC patients during their first treatment cycle. Whole-body planar images were acquired at 1 ± 0.5, 4 ± 0.5, 24 ± 2, 48 ± 2, 72 ± 2, and 144 ± 2 h post-injection, with SPECT/CT images obtained at 24 ± 2 h. Absorbed doses were calculated for five organs and the entire metastasis regions using GATE, OLINDA, and IDAC platforms. The spherical method was used to determine and compare the absorbed doses in metastatic regions and undefined organs in OLINDA and IDAC Phantom.

Results: The organ-absorbed dose calculations produced by GATE were consistent with those obtained from OLINDA and IDAC. The average percentage differences in absorbed dose for all organs between Monte Carlo calculations and the estimated from IDAC and OLINDA were -0.24 ± 2.14% and 5.16 ± 5.66%, respectively. There was a significant difference between GATE and both IDAC (17.55 ± 29.1%) and OLINDA (25.86 ± 18.04%) in determining absorbed doses to metastatic areas using the spherical model.

Conclusion: The absorbed dose of organs in the first treatment cycle remained below tolerable limits. However, cumulative absorbed doses should be considered for the administered activities in the next cycles of treatment. While Monte Carlo, IDAC, and OLINDA results were aligned for organ dose calculations, patient-specific dosimetry may be necessary due to anatomical and functional changes. Accurate dose estimation for undefined organs and metastatic regions using the spherical model is significantly influenced by tissue density, highlighting the value of CT imaging.

Background: Continuously monitored external dose-rate signals from remote dose-rate meters (DRMs) were analyzed to determine the effective half-life (T_eff) of ¹³¹I in differentiated thyroid cancer (DTC) patients. The aim is to gain novel understanding of the excretion of radioactive iodine (RAI) in DTC patients and to demonstrate that a remote DRM system can be reliably used for real-time monitoring of external dose-rates of DTC patients.

Methods: 110 DTC patients who received postoperative RAI therapy between September 2018 and February 2023 in Turku University Hospital were studied retrospectively. The external dose-rates of the patients were continuously monitored during their hospitalization with a remote DRM fixed in the ceiling of the isolation room. Generalized linear mixed model (GLMM) was used to analyse the association between logarithmical T_eff and patient characteristics.

Results: The median T_eff for all patients was 12.60 h (Q1: 10.35; Q3: 14.75 h). Longer T_effs were associated with higher BMI (p = 0.004), lower GFR (p < 0.001), and diabetes (p = 0.007). Our study also revealed that neither age nor subsequent RAI therapies have a significant impact on the whole body T_eff (p = 0.522 and p = 0.414, respectively).

Conclusion: Patients with higher BMI, decreased GFR, or diabetes have a longer whole-body T_eff of ¹³¹I. Ceiling-mounted remote DMRs can reliably be used to determine patient's T_eff. Since T_eff values vary among patients, ceiling-mounted meters can be used to optimize the length of radiation isolation period at the hospital while improving patient comfort and staff efficiency.

Background: Long-axial field-of-view (LAFOV) Positron Emission Tomography (PET) scanners provide high sensitivity, but throughput is limited because of time-consuming patient positioning. To enhance throughput, a novel Walk-Through PET (WT-PET) scanner has been developed, allowing patients to stand upright, supported by an adjustable headrest and hand supports. This study evaluates the degree of motion in the WT-PET system and compares it with the standard PET-CT.

Methods: Three studies were conducted with healthy volunteers to estimate motion. The first two studies assessed motion in the WT-PET's Design I (Study 1) and Design II (Study 2), while the third study compared motion on a standard PET-CT scanner bed (Study 3). Infrared markers placed on the head, shoulders, chest, and abdomen were tracked and processed using image-processing techniques involving thresholding and connected component analysis. Videos were recorded for normal breathing and breath-holding conditions, and 2D centroids were transformed into 3D coordinates using depth information.

Results: The results shows a significant reduction in motion during breath-holding, especially for the abdomen. Mean motion distances decreased from 2.63 mm to 2.18 mm in Study 1 and from 2.42 mm to 1.67 mm in Study 2. Statistical analysis revealed notable differences in motion between the WT-PET and mCT scanners. The Shapiro-Wilk test indicated non-normal motion distributions in the head, right shoulder, and abdomen for both systems, leading to the use of the Wilcoxon signed-rank test for all markers. Significant differences were found in the right shoulder (p = 0.0266), left shoulder (p = 0.0004) and chest (p < 0.0001) but no significant differences were observed in the head (p = 0.1327) and abdomen (p = 0.8404).

Conclusion: This study provides a comprehensive analysis of patient motion in a WT-PET scanner with respect to the standard PET. The findings highlight a significant increase in shoulder and chest motion, while the head and abdomen regions showed more stability.

Background: The tin filter has allowed radiation dose reduction in some standalone diagnostic computed tomography (CT) applications. Yet, 'low-dose' CT scans are commonly used in positron emission tomography (PET)-CT for lesion localisation/characterisation (L/C), with higher noise tolerated. Thus, dose reductions permissible with the tin filter at this image quality level may differ. The aim was to determine the level of CT dose reduction permitted with the tin filter in PET-CT, for comparable image quality to the clinical reference standard (CRS) L/C CT images acquired with standard filtration.

Materials and methods: A whole-body CT phantom was scanned with standard filtration in CRS protocols, using 120 kV with 20mAs-ref for bone L/C (used in ¹⁸F-Sodium Fluoride (NaF) PET-CT) and 40mAs-ref for soft tissue L/C (used in ¹⁸F-Fluorodeoxyglucose (FDG) PET-CT), followed by tin filter scans at 100 kV (Sn100kV) and 140 kV (Sn140kV) with a range of mAs settings. For each scan, effective dose (ED) in an equivalent-sized patient was calculated, and image quality determined in 5 different tissues through quantitative (contrast-to-noise ratio) and qualitative (visual) analyses. The relative dose reductions which could be achieved with the tin filter for comparable image quality to CRS images were calculated.

Results: Quantitative analysis demonstrated dose savings of 50-76% in bone, 27-51% in lung and 8-61% in soft tissue with use of the tin filter at Sn100kV. Qualitative analysis demonstrated dose reductions using Sn100kV in general agreement with the dose reductions indicated by quantitative analysis. Overall, CT dose reductions of around 85% were indicated for NaF bone PET-CT, allowing whole-body CT at just 0.2mSv ED, and a 30-40% CT dose reduction for FDG PET-CT using Sn100kV (1.7-2.0mSv), providing comparable image quality to current CRS images with standard filtration. Sn140kV demonstrated limited value in CT dose reduction.

Conclusions: Large CT dose reductions can be made using the tin filter at Sn100kV, when imaging bone, lung and soft tissue at L/C level CT image quality in PET-CT. As well as reducing the risk of inducing a cancer in later life, such dose reductions may also impact PET-CT practice, such as justifying cross-sectional over planar imaging or justifying PET-CT in younger patients.

Background: Radiopharmaceutical therapy with ²²⁵Ac- and ¹⁷⁷Lu-PSMA has shown promising results for the treatment of prostate cancer. However, the distinct physical properties of alpha and beta radiation elicit varying cellular responses, which could be influenced by factors such as tumour morphology. In this study, we use simulations to examine how cell geometry, region of pharmaceutical uptake within the cell to model different internalization fractions, and the presence of tumour hypoxia and necrosis impact nucleus absorbed doses and dose heterogeneity with ²²⁵Ac and ¹⁷⁷Lu. We also develop nucleus absorbed dose kernels for application to autoradiography images.

Methods: We used the GATE Monte Carlo software to simulate three geometries of LNCaP prostate cancer cells (spherical, cubic, and ovoid) with activity of ²²⁵Ac or ¹⁷⁷Lu internalized in the cytoplasm or bound to the extracellular membrane. Nucleus S-values were calculated for each geometry, source region, and isotope. The cell models were used to create nucleus absorbed dose kernels for each source region describing the dose to each nucleus in a cell layer, which were applied to simulated tumours composed of normoxic, hypoxic, or necrotic cancer cells to obtain dose rate maps. Absorbed doses within the tumours and dose heterogeneity were analyzed for each tumour morphology and isotope. Cell geometry made a minimal impact on S-values to the nucleus, however internalization resulted in higher nucleus doses. Applying the kernels to the simulated tumour maps showed that doses to each cell type varied between ²²⁵Ac and ¹⁷⁷Lu depending on tumour morphology. Dose heterogeneity within tumours was slightly higher with ²²⁵Ac, however the tumour morphology made a larger impact on dose heterogeneity compared to the choice of isotope, with hypoxic and necrotic tumours having very heterogeneous dose distributions.

Conclusions: Cell geometry simplifications may still allow robust results in simulation studies. Furthermore, the morphology of the tumour itself may make a larger impact on treatment response compared to other variables such as ratio of internalization. Finally, nucleus absorbed dose kernels were created that could enable microdosimetric studies with autoradiography.

Purpose: This study aims to evaluate the accuracy of four kidney depth measurement methods-nuclear medicine tomography, nuclear medicine lateral scanning, ultrasound, and Tonnesen's formula-based estimation-using CT measurements as the reference standard. Additionally, it investigates the feasibility of utilizing nuclear medicine tomography and lateral scanning for measuring kidney depth in ^99mTc-DTPA renal dynamic imaging.

Methods: Hollow kidney phantoms mimicking the shape and volume of adult kidneys were 3D printed and filled with ^99mTcO₄^- solution. These phantoms were then subjected to lateral scanning and nuclear medicine tomography using CZT (cadmium-zinc-telluride) SPECT/CT to determine the optimal post-processing method. Forty patients who underwent renal dynamic imaging were recruited for the study. Renal depths were derived from ultrasound, lateral imaging, nuclear medicine tomography, formula-based estimation, and CT measurements. The renal depths obtained through these four methods were for correlation with CT-measured renal depths. Additionally, the absolute differences between renal depths obtained by each method and the CT standard were analyzed and compared across groups.

Results: Using kidney phantoms, nuclear medicine tomography images were processed with a Butterworth filter (cutoff frequency = 0.6), and renal outlines in lateral images was manually delineated. In the clinical validation phase, correlation coefficients indicated strong associations between renal depths measured by nuclear medicine tomography (left kidney: R = 0.885, P < 0.05; right kidney: R = 0.927, P < 0.05) and lateral scanning (left kidney: R = 0.933, P < 0.05; right kidney: R = 0.956, P < 0.05) compared to CT measurements. The difference in kidney depth between nuclear medicine tomography and CT measurements were the smallest and statistically significant (left kidney: 0.69 ± 0.51; right kidney: 0.58 ± 0.41, P < 0.05).

Conclusion: Using ordered subset expectation maximization (OSEM) in conjunction with a Butterworth filter (fc = 0.6) as the post-processing method, nuclear medicine tomography enables more accurate renal depth measurements without increasing the radiation dose to patients.

Background: The radiation exposure of nuclear medicine personnel, especially concerning extremity doses, has been a significant focus over the past two decades. This study addresses the evolving practice of NM, particularly with the rise of radionuclide therapy and theranostic procedures, which involve a variety of radionuclides such as ⁶⁸Ga, ¹⁷⁷Lu, and ¹³¹I. Traditional studies have concentrated on common radioisotopes like ^99mTc, ¹⁸F, and ⁹⁰Y, but there is limited data on these radionuclides, which are more and more frequently used. This study, part of the European SINFONIA project, aims to fill this gap by providing new dosimetry data through a multicenter approach. The research monitors extremity doses to hands, eye lens doses, and whole-body doses in nuclear medicine staff handling ⁶⁸Ga, ¹⁷⁷Lu, and ¹³¹I. It examines the type of activities performed and the protective measures used. The study extrapolates measured doses to annual doses, comparing them with annual dose limits, and assesses the contribution of these specific procedures to the overall occupational dose of nuclear medicine personnel.

Results: Measurements were conducted from November 2020 to August 2023 across nine hospitals. The highest whole-body, eye lens and extremity doses were observed for ⁶⁸Ga. Average maximum extremity doses, normalized per manipulated activity, were found of 6200 µSv/GBq, 30 µSv/GBq and 260 µSV/GBq for ⁶⁸Ga, ¹⁷⁷Lu and ¹³¹I, respectively. Average whole-body doses stayed below 60 µSv/GBq for all 3 isotopes and below 200 µSv/GBq for the eye lens dose. The variation in doses also depends on the task performed. For ⁶⁸Ga there is a risk of reaching the annual dose limit for skin dose during synthesis and dispensing.

Conclusions: This study's measurement campaigns across various European countries have provided new and extensive occupational dosimetry data for nuclear medicine staff handling ⁶⁸Ga, ¹⁷⁷Lu and ¹³¹I radiopharmaceuticals. The results indicate that ⁶⁸Ga contributes significantly to the global occupational dose, despite its relatively low usage compared to other isotopes. Staff working in radiopharmacy hot labs, labeling and dispensing ¹⁷⁷Lu contribute less to the finger dose compared to other isotopes.