| 201. |
- Pretorius, P. Hendrik, et al.
(författare)
-
Monte Carlo Simulations of the GE Discovery Alcyone CZT SPECT Systems
- 2015
-
Ingår i: IEEE Transactions on Nuclear Science. - 0018-9499. ; 62:3, s. 832-839
-
Tidskriftsartikel (refereegranskat)abstract
- Compact SPECT systems with cadmium zinc telluride (CZT) solid-state detectors with improved energy resolution and shorter acquisition times have recently been introduced. These systems have, however, different energy characteristics compared to NaI(Tl) crystal-based cameras; therefore, a need exists to develop new simulation models for these cameras. We modeled the charge transport within the CZT detectors for a GE Discovery 530c/570c SPECT system with multiple pinhole collimators employing the SIMIND Monte Carlo program and validated simulations against measurements. The incomplete charge collection between the anode and cathode in the pixilated CZT was modeled with the Hecht equation. The simulation also included charge-sharing effects across pixels due to physical interactions and charge diffusion. To validate our CZT-model, Tc-99m and I-123 point sources and a Tl-201 line source were acquired and measured. Measured energy spectra were compared with simulated energy spectra. The Monte Carlo simulated energy spectra agreed well with the experimental measurements within the photopeak, overestimated the k-edge x-ray escape peaks of cadmium and telluride, and slightly underestimated the remainder of the tail. Comparisons of system sensitivity and spatial resolution were also conducted for an array of point source locations with results showing excellent agreement. Lastly, to demonstrate a clinically realistic case, a simulation of an anthropomorphic phantom with a cardiac insert and an inferior defect was performed. Simulated projections were processed using the GE Xeleris software confirming the accuracy of the SIMIND geometry. We conclude that it is feasible to simulate the GE Discovery 530c/570c SPECT system using the SIMIND code.
|
|
| 202. |
- Purdue, Mark P, et al.
(författare)
-
Genome-wide association study of renal cell carcinoma identifies two susceptibility loci on 2p21 and 11q13.3
- 2011
-
Ingår i: Nature Genetics. - : Springer Science and Business Media LLC. - 1061-4036 .- 1546-1718. ; 43:1, s. 60-65
-
Tidskriftsartikel (refereegranskat)abstract
- We conducted a two-stage genome-wide association study of renal cell carcinoma (RCC) in 3,772 affected individuals (cases) and 8,505 controls of European background from 11 studies and followed up 6 SNPs in 3 replication studies of 2,198 cases and 4,918 controls. Two loci on the regions of 2p21 and 11q13.3 were associated with RCC susceptibility below genome-wide significance. Two correlated variants (r² = 0.99 in controls), rs11894252 (P = 1.8 × 10⁻⁸) and rs7579899 (P = 2.3 × 10⁻⁹), map to EPAS1 on 2p21, which encodes hypoxia-inducible-factor-2 alpha, a transcription factor previously implicated in RCC. The second locus, rs7105934, at 11q13.3, contains no characterized genes (P = 7.8 × 10⁻¹⁴). In addition, we observed a promising association on 12q24.31 for rs4765623, which maps to SCARB1, the scavenger receptor class B, member 1 gene (P = 2.6 × 10⁻⁸). Our study reports previously unidentified genomic regions associated with RCC risk that may lead to new etiological insights.
|
|
| 203. |
- Ravaud, Alain, et al.
(författare)
-
Adjuvant Sunitinib in High-Risk Renal-Cell Carcinoma after Nephrectomy.
- 2016
-
Ingår i: New England Journal of Medicine. - 0028-4793 .- 1533-4406. ; 375:23, s. 2246-2254
-
Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Sunitinib, a vascular endothelial growth factor pathway inhibitor, is an effective treatment for metastatic renal-cell carcinoma. We sought to determine the efficacy and safety of sunitinib in patients with locoregional renal-cell carcinoma at high risk for tumor recurrence after nephrectomy.METHODS: In this randomized, double-blind, phase 3 trial, we assigned 615 patients with locoregional, high-risk clear-cell renal-cell carcinoma to receive either sunitinib (50 mg per day) or placebo on a 4-weeks-on, 2-weeks-off schedule for 1 year or until disease recurrence, unacceptable toxicity, or consent withdrawal. The primary end point was disease-free survival, according to blinded independent central review. Secondary end points included investigator-assessed disease-free survival, overall survival, and safety.RESULTS: The median duration of disease-free survival was 6.8 years (95% confidence interval [CI], 5.8 to not reached) in the sunitinib group and 5.6 years (95% CI, 3.8 to 6.6) in the placebo group (hazard ratio, 0.76; 95% CI, 0.59 to 0.98; P=0.03). Overall survival data were not mature at the time of data cutoff. Dose reductions because of adverse events were more frequent in the sunitinib group than in the placebo group (34.3% vs. 2%), as were dose interruptions (46.4% vs. 13.2%) and discontinuations (28.1% vs. 5.6%). Grade 3 or 4 adverse events were more frequent in the sunitinib group (48.4% for grade 3 events and 12.1% for grade 4 events) than in the placebo group (15.8% and 3.6%, respectively). There was a similar incidence of serious adverse events in the two groups (21.9% for sunitinib vs. 17.1% for placebo); no deaths were attributed to toxic effects.CONCLUSIONS: Among patients with locoregional clear-cell renal-cell carcinoma at high risk for tumor recurrence after nephrectomy, the median duration of disease-free survival was significantly longer in the sunitinib group than in the placebo group, at a cost of a higher rate of toxic events. (Funded by Pfizer; S-TRAC ClinicalTrials.gov number, NCT00375674 .).
|
|
| 204. |
|
|
| 205. |
- Rong, Xing, et al.
(författare)
-
Development and evaluation of an improved quantitative Y-90 bremsstrahlung SPECT method
- 2012
-
Ingår i: Medical Physics. - : Wiley. - 0094-2405. ; 39:5, s. 2346-2358
-
Tidskriftsartikel (refereegranskat)abstract
- Purpose: Yttrium-90 (Y-90) is one of the most commonly used radionuclides in targeted radionuclide therapy (TRT). Since it decays with essentially no gamma photon emissions, surrogate radionuclides (e.g., In-111) or imaging agents (e.g., Tc-99m MAA) are typically used for treatment planning. It would, however, be useful to image Y-90 directly in order to confirm that the distributions measured with these other radionuclides or agents are the same as for the Y-90 labeled agents. As a result, there has been a great deal of interest in quantitative imaging of Y-90 bremsstrahlung photons using single photon emission computed tomography (SPECT) imaging. The continuous and broad energy distribution of bremsstrahlung photons, however, imposes substantial challenges on accurate quantification of the activity distribution. The aim of this work was to develop and evaluate an improved quantitative Y-90 bremsstrahlung SPECT reconstruction method appropriate for these imaging applications. Methods: Accurate modeling of image degrading factors such as object attenuation and scatter and the collimator-detector response is essential to obtain quantitatively accurate images. All of the image degrading factors are energy dependent. Thus, the authors separated the modeling of the bremsstrahlung photons into multiple categories and energy ranges. To improve the accuracy, the authors used a bremsstrahlung energy spectrum previously estimated from experimental measurements and incorporated a model of the distance between Y-90 decay location and bremsstrahlung emission location into the SIMIND code used to generate the response functions and kernels used in the model. This improved Monte Carlo bremsstrahlung simulation was validated by comparison to experimentally measured projection data of a Y-90 line source. The authors validated the accuracy of the forward projection model for photons in the various categories and energy ranges using the validated Monte Carlo (MC) simulation method. The forward projection model was incorporated into an iterative ordered subsets-expectation maximization (OS-EM) reconstruction code to allow for quantitative SPECT reconstruction. The resulting code was validated using both a physical phantom experiment with spherical objects in a warm background and a realistic anatomical phantom simulation. In the physical phantom study, the authors evaluated the method in terms of quantitative accuracy of activity estimates in the spheres; in the simulation study, the authors evaluated the accuracy and precision of activity estimates from various organs and compared them to results from a previously proposed method. Results: The authors demonstrated excellent agreement between the experimental measurement and Monte Carlo simulation. In the XCAT phantom simulation, the proposed method achieved much better accuracy in the modeling (error in photon counts was -1.1 %) compared to a previously proposed method (errors were more than 20 %); the quantitative accuracy of activity estimates was excellent for all organs (errors were from -1.6 % to 11.9 %) and comparable to previously published results for I-131 using the same collimator. Conclusions: The proposed Y-90 bremsstrahlung SPECT reconstruction method provided very accurate estimates of organ activities, with accuracies approaching those previously observed for I-131. The method may be useful in verifying organ doses for targeted radionuclide therapy using Y-90. (C) 2012 American Association of Physicists in Medicine. [http://dx.doi.org/10.1118/1.3700174]
|
|
| 206. |
|
|
| 207. |
- Roth, Daniel, et al.
(författare)
-
Assessment of a hand-held CZT-based gamma camera for pre-clinical imaging of 177Lu
- 2023
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A small CdZnTe-based hand-held gamma-camera has been acquired, intended to be used for preclinical imaging. The camera produces images of size 4 cm x 4 cm with an image-matrix of 16 x 16 pixels and can be equipped with a low-energy high-sensitivity (LEHS) or a high-resolution (LEHR) parallel-hole collimator. Pre-clinical imaging involves scales smaller than what the camera is typically used for, and dedicated assessment of the camera’s performance in this field is thus warranted and the aim of this work. To this end, a mouse-like phantom is developed with the MOBY computer phantom as a basis and manufactured through 3D-printing. The phantom is printed in PLA, with fillable cavities for the liver and a tumour. Additionally, a motorised platform is built enabling SPECT acquisitions by rotating an object in front of the camera. Software is developed in-house for camera operation, SPECT acquisition, and tomographic reconstruction. The camera’s performance for 177 Lu imaging is assessed through measurements on the imageuniformity, sensitivity, spatial resolution, as well as planar and SPECT acquisitions on the mouse phantom. Energy windows over the 55 keV, 113 keV, and 208 keV photopeaks are investigated. Obtained sensitivities are around 100 cps/MBq for the LEHS collimator and 20 cps/MBq for the LEHR collimator, meaning that quick acquisitions can be made with 177 Lu activity administrations that are typically used pre-clinically. Tomographic reconstructions demonstrates that the camera can be used for SPECT applications. Overall, the camera is found promising for pre-clinical applications, both for planar and SPECT imaging.
|
|
| 208. |
- Roth, Daniel, et al.
(författare)
-
Feasibility of 177Lu activity quantification using a small portable CZT-based gamma-camera
- 2024
-
Ingår i: EJNMMI Physics. - 2197-7364. ; 11:1
-
Tidskriftsartikel (refereegranskat)abstract
- Background: In image processing for activity quantification, the end goal is to produce a metric that is independent of the measurement geometry. Photon attenuation needs to be accounted for and can be accomplished utilizing spectral information, avoiding the need of additional image acquisitions. The aim of this work is to investigate the feasibility of 177Lu activity quantification with a small CZT-based hand-held gamma-camera, using such an attenuation correction method. Methods: A previously presented dual photopeak method, based on the differential attenuation for two photon energies, is adapted for the three photopeaks at 55 keV, 113 keV, and 208 keV for 177Lu. The measurement model describes the count rates in each energy window as a function of source depth and activity, accounting for distance-dependent system sensitivity, attenuation, and build-up. Parameter values are estimated from characterizing measurements, and the source depth and activity are obtained by minimizing the difference between measured and modelled count rates. The method is applied and evaluated in phantom measurements, in a clinical setting for superficial lesions in two patients, and in a pre-clinical setting for one human tumour xenograft. Evaluation is made for a LEHR and an MEGP collimator. Results: For phantom measurements at clinically relevant depths, the average (and standard deviation) in activity errors are 17% ± 9.6% (LEHR) and 2.9% ± 3.6% (MEGP). For patient measurements, deviations from activity estimates from planar images from a full-sized gamma-camera are 0% ± 21% (LEHR) and 16% ± 18% (MEGP). For mouse measurements, average deviations of − 16% (LEHR) and − 6% (MEGP) are obtained when compared to a small-animal SPECT/CT system. The MEGP collimator appears to be better suited for activity quantification, yielding a smaller variability in activity estimates, whereas the LEHR results are more severely affected by septal penetration. Conclusions: Activity quantification for 177Lu using the hand-held camera is found to be feasible. The readily available nature of the hand-held camera may enable more frequent activity quantification in e.g., superficial structures in patients or in the pre-clinical setting.
|
|
| 209. |
|
|
| 210. |
- Roth, Daniel, et al.
(författare)
-
Monte Carlo modelling of a compact CZT-based gamma camera with application to 177Lu imaging
- 2022
-
Ingår i: EJNMMI Physics. - : Springer Science and Business Media LLC. - 2197-7364. ; 9:1
-
Tidskriftsartikel (refereegranskat)abstract
- Background: Semiconductor gamma-camera systems based on cadmium zinc telluride (CZT) detectors present new challenges due to an energy-response that includes effects of low-energy tailing. In particular, such energy tails produce effects that need to be considered when imaging radionuclides with multiple emissions such as 177Lu. Monte Carlo simulation can be used to investigate the behaviour of such systems and optimise their use, provided that the detector model closely reflects the real physical detector. The aim of this work is to develop a CZT model applicable for simulation of CZT-based gamma cameras. Methods: The equations describing the charge transport and signal induction are considered in three dimensions and are solved numerically, and the CZT model is then realised by coupling the detector-response to the photon-transport handled by the SIMIND Monte Carlo program. The CZT model is tuned to reproduce experimentally measured energy spectra of a hand-held gamma camera system for multiple radionuclides (99 mTc , 123I and 177Lu ) and parallel-hole collimators (MEGP, LEHR) as well as an uncollimated system. Results: Overall, the model results agree well with measurements across the range of experimental conditions. The applicability of the model is demonstrated by separating energy spectra into components to investigate the interference of high-energy photons on lower energy-windows, where pronounced effects of low-energy tailing for 177Lu are observed. Conclusions: The developed model provides understanding of the specifics of the camera response and is expected to be helpful for future optimisation of gamma camera applications.
|
|
