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Sökning: L773:1361 6560 > Sjögreen Gleisner Katarina

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1.
  • Brolin, Gustav, et al. (författare)
  • Dynamic (99m)Tc-MAG3 renography: images for quality control obtained by combining pharmacokinetic modelling, an anthropomorphic computer phantom and Monte Carlo simulated scintillation camera imaging.
  • 2013
  • Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 58:10, s. 3145-3161
  • Tidskriftsartikel (refereegranskat)abstract
    • In dynamic renal scintigraphy, the main interest is the radiopharmaceutical redistribution as a function of time. Quality control (QC) of renal procedures often relies on phantom experiments to compare image-based results with the measurement setup. A phantom with a realistic anatomy and time-varying activity distribution is therefore desirable. This work describes a pharmacokinetic (PK) compartment model for (99m)Tc-MAG3, used for defining a dynamic whole-body activity distribution within a digital phantom (XCAT) for accurate Monte Carlo (MC)-based images for QC. Each phantom structure is assigned a time-activity curve provided by the PK model, employing parameter values consistent with MAG3 pharmacokinetics. This approach ensures that the total amount of tracer in the phantom is preserved between time points, and it allows for modifications of the pharmacokinetics in a controlled fashion. By adjusting parameter values in the PK model, different clinically realistic scenarios can be mimicked, regarding, e.g., the relative renal uptake and renal transit time. Using the MC code SIMIND, a complete set of renography images including effects of photon attenuation, scattering, limited spatial resolution and noise, are simulated. The obtained image data can be used to evaluate quantitative techniques and computer software in clinical renography.
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2.
  • Brolin, Gustav, et al. (författare)
  • Pharmacokinetic digital phantoms for accuracy assessment of image-based dosimetry in (177)Lu-DOTATATE peptide receptor radionuclide therapy.
  • 2015
  • Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 60:15, s. 6131-6149
  • Tidskriftsartikel (refereegranskat)abstract
    • Patient-specific image-based dosimetry is considered to be a useful tool to limit toxicity associated with peptide receptor radionuclide therapy (PRRT). To facilitate the establishment and reliability of absorbed-dose response relationships, it is essential to assess the accuracy of dosimetry in clinically realistic scenarios. To this end, we developed pharmacokinetic digital phantoms corresponding to patients treated with (177)Lu-DOTATATE. Three individual voxel phantoms from the XCAT population were generated and assigned a dynamic activity distribution based on a compartment model for (177)Lu-DOTATATE, designed specifically for this purpose. The compartment model was fitted to time-activity data from 10 patients, primarily acquired using quantitative scintillation camera imaging. S values for all phantom source-target combinations were calculated based on Monte-Carlo simulations. Combining the S values and time-activity curves, reference values of the absorbed dose to the phantom kidneys, liver, spleen, tumours and whole-body were calculated. The phantoms were used in a virtual dosimetry study, using Monte-Carlo simulated gamma-camera images and conventional methods for absorbed-dose calculations. The characteristics of the SPECT and WB planar images were found to well represent those of real patient images, capturing the difficulties present in image-based dosimetry. The phantoms are expected to be useful for further studies and optimisation of clinical dosimetry in (177)Lu PRRT.
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3.
  • Gustafsson, Johan Ruben, et al. (författare)
  • On the biologically effective dose (BED)-using convolution for calculating the effects of repair: I. Analytical considerations.
  • 2013
  • Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 58:5, s. 1507-1527
  • Tidskriftsartikel (refereegranskat)abstract
    • This work presents a new mathematical formulation of biologically effective dose (BED) for radiation therapy where effects of repair need to be considered. The formulation is based on the observation that the effects of repair, both during protracted irradiation and of incomplete repair between fractions, can be written using a convolution, i.e. [Formula: see text] where T is the total irradiation time, R(T)(t) is the absorbed dose rate as a function of time t and I(t) is the function describing repair. To validate this formulation, the previously published expressions for instant and protracted irradiation are first summarized. Then, by analytical derivation, it is shown that the new formulation gives identical results. The calculation of BED can thus be treated within one single mathematical framework, applicable in external beam therapy, brachytherapy, radionuclide therapy, or a combination of these treatment modalities. Moreover, the new formulation allows for a straightforward incorporation of different repair models and has the advantage of being numerically applicable.
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4.
  • Gustafsson, Johan Ruben, et al. (författare)
  • On the biologically effective dose (BED)-using convolution for calculating the effects of repair: II. Numerical considerations.
  • 2013
  • Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 58:5, s. 1529-1548
  • Tidskriftsartikel (refereegranskat)abstract
    • We have previously shown analytically that the biologically effective dose (BED), including effects of repair during irradiation and of incomplete repair between fractions, can be formulated using a convolution between the absorbed dose rate function and the function describing repair. In this work, a discrete formalism is derived along with its implementation via the fast Fourier transform. The implementation takes the intrinsic periodicity of the discrete Fourier transform into consideration, as well as possible inconsistencies that may arise due to discretization and truncation of the functions describing the absorbed dose rate and repair. Numerically and analytically calculated BED values are compared for various situations in external beam radiotherapy, brachytherapy and radionuclide therapy, including the use of different repair models. The numerical method is shown to be accurate and versatile since it can be applied to any kind of absorbed dose rate function and allows for the incorporation of different repair models. Typical accuracies for clinically realistic examples are in the order of 10(-3)% to 10(-5)%. The method has thus the potential of being a useful tool for the calculation of BED, also in situations with complicated irradiation patterns or repair functions.
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5.
  • Gustafsson, Johan Ruben, et al. (författare)
  • Uncertainty propagation for SPECT/CT-based renal dosimetry in (177)Lu peptide receptor radionuclide therapy.
  • 2015
  • Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 60:21, s. 8329-8346
  • Tidskriftsartikel (refereegranskat)abstract
    • A computer model of a patient-specific clinical (177)Lu-DOTATATE therapy dosimetry system is constructed and used for investigating the variability of renal absorbed dose and biologically effective dose (BED) estimates. As patient models, three anthropomorphic computer phantoms coupled to a pharmacokinetic model of (177)Lu-DOTATATE are used. Aspects included in the dosimetry-process model are the gamma-camera calibration via measurement of the system sensitivity, selection of imaging time points, generation of mass-density maps from CT, SPECT imaging, volume-of-interest delineation, calculation of absorbed-dose rate via a combination of local energy deposition for electrons and Monte Carlo simulations of photons, curve fitting and integration to absorbed dose and BED. By introducing variabilities in these steps the combined uncertainty in the output quantity is determined. The importance of different sources of uncertainty is assessed by observing the decrease in standard deviation when removing a particular source. The obtained absorbed dose and BED standard deviations are approximately 6% and slightly higher if considering the root mean square error. The most important sources of variability are the compensation for partial volume effects via a recovery coefficient and the gamma-camera calibration via the system sensitivity.
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6.
  • Meerkhan, Suaad, et al. (författare)
  • Testis dosimetry in individual patients by combining a small-scale dosimetry model and pharmacokinetic modeling-application of (111)In-Ibritumomab Tiuxetan (Zevalin(®)).
  • 2014
  • Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 59:24, s. 7889-7904
  • Tidskriftsartikel (refereegranskat)abstract
    • A heterogeneous distribution of radionuclides emitting low-energy electrons in the testicles may result in a significant difference between an absorbed dose to the radiosensitive spermatogonia and the mean absorbed dose to the whole testis. This study focused on absorbed dose distribution in patients at a finer scale than normally available in clinical dosimetry, which was accomplished by combining a small-scale dosimetry model with patient pharmacokinetic data. The activity in the testes was measured and blood sampling was performed for patients that underwent pre-therapy imaging with (111)In-Zevalin(®). Using compartment modeling, testicular activity was separated into two components: vascular and extravascular. The uncertainty of absorbed dose due to geometry variations between testicles was explored by an assumed activity micro-distribution and by varying the radius of the interstitial tubule. Results showed that the absorbed dose to germ cells might be strongly dependent on the location of the radioactive source, and may exceed the absorbed dose to the whole testis by as much as a factor of two. Small-scale dosimetry combined with compartmental analysis of clinical data proved useful for gauging tissue dosimetry and interpreting how intrinsic geometric variation influences the absorbed dose.
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7.
  • Minarik, David, et al. (författare)
  • Evaluation of quantitative (90)Y SPECT based on experimental phantom studies.
  • 2008
  • Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 53:20, s. 5689-5703
  • Tidskriftsartikel (refereegranskat)abstract
    • In SPECT imaging of pure beta emitters, such as (90)Y, the acquired spectrum is very complex, which increases the demands on the imaging protocol and the reconstruction. In this work, we have evaluated the quantitative accuracy of bremsstrahlung SPECT with focus on the reconstruction algorithm including model-based attenuation, scatter and collimator-detector response (CDR) compensations. The scatter and CDR compensation methods require pre-calculated point-spread functions, which were generated with the SIMIND MC program. The SIMIND program is dedicated for simulation of scintillation camera imaging and only handles photons. The aim of this work was therefore twofold. The first aim was to implement simulation of bremsstrahlung imaging into the SIMIND code and to validate simulations against experimental measurements. The second was to investigate the quality of bremsstrahlung SPECT imaging and to evaluate the possibility of quantifying the activity in differently shaped sources. In addition, a feasibility test was performed on a patient that underwent treatment with (90)Y-Ibritumomab tiuxetan (Zevalin(R)). The MCNPX MC program was used to generate bremsstrahlung photon spectra which were used as source input in the SIMIND program. The obtained bremsstrahlung spectra were separately validated by experimental measurement using a HPGe detector. Validation of the SIMIND generated images was done by a comparison to gamma camera measurements of a syringe containing (90)Y. Results showed a slight deviation between simulations and measurements in image regions outside the source, but the agreement was sufficient for the purpose of generating scatter and CDR kernels. For the bremsstrahlung SPECT experiment, the RSD torso phantom with (90)Y in the liver insert was measured with and without background activities. Projection data were obtained using a GE VH/Hawkeye system. Image reconstruction was performed by using the OSEM algorithm with and without different combinations of model-based attenuation, scatter and CDR compensations. The reconstructed images were then evaluated in terms of the accuracy of the total activity estimate in the liver insert. It was found that the activity in a large source such as the liver was estimated with a bias of around -70%, when no compensations were included in the reconstruction, whereas when compensations were included the bias obtained was between -10 and 16%. It is concluded that although the (90)Y bremsstrahlung spectrum is continuous with no pronounced peak and the count rate is low, it is possible to achieve reasonably accurate activity estimates from bremsstrahlung SPECT images if proper compensations are applied in the reconstruction. This conclusion was also confirmed by the patient study.
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8.
  • Minarik, David, et al. (författare)
  • Evaluation of quantitative planar (90)Y bremsstrahlung whole-body imaging.
  • 2009
  • Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 54:19, s. 5873-5883
  • Tidskriftsartikel (refereegranskat)abstract
    • With high-dose administration of (90)Y labeled antibodies, it is possible to image (90)Y without an admixture of (111)In. We have earlier shown that it is possible to perform quantitative (90)Y bremsstrahlung SPECT for dosimetry purposes with reasonable accuracy. However, whole-body (WB) activity quantification with the conjugate view method is not as time consuming as SPECT and has been the method of choice for dosimetry. We have investigated the possibility of using a conjugate view method where scatter-, backscatter- and septal-penetration compensations are performed by inverse filtering and attenuation correction is performed with a WB x-ray image, for total-body and organ activity quantification of (90)Y. The method was evaluated using both Monte Carlo simulated scintillation camera images using realistic source distributions, and by an experimental phantom study. The method was evaluated in terms of image quality and accuracy of the activity quantification. The experimental phantom study was performed using the RSD torso phantom with (90)Y activity uniformly distributed in the liver insert. A GE Discovery VH/Hawkeye system was used to acquire the image. The simulation study was performed for a realistic activity distribution in the NCAT anthropomorphic phantom where (90)Y bremsstrahlung images were generated using the SIMIND MC program. Two different phantom configurations and two activity distributions were simulated. To mimic the RSD phantom experiment one simulation study was also made with (90)Y activity located only in the liver. The SIMIND program was configured to resemble a GE Discovery VH/Hawkeye system. An x-ray projector program was used to generate whole-body x-ray images from the NCAT phantom for attenuation correction in the conjugate view method. Organ activities were calculated from ROIs that exactly covered the organs. Corrections for background activity, overlapping activity and source extension in the depth direction were applied on the ROI data. The total-body activities for the simulated images were generally overestimated by around 10%, which is reasonable since the correction for source extension was not applied on the total-body values. The accuracy of the organ activities was mostly within 15% for both the simulation study and the experimental study. The results suggest that it is possible to quantify (90)Y activity in ROIs with reasonable accuracy using this method.
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9.
  • Minguez Gabina, Pablo, et al. (författare)
  • Biologically effective dose in fractionated molecular radiotherapy-application to treatment of neuroblastoma with (131)I-mIBG.
  • 2016
  • Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 61:6, s. 2532-2551
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work, the biologically effective dose (BED) is investigated for fractionated molecular radiotherapy (MRT). A formula for the Lea-Catcheside G-factor is derived which takes the possibility of combinations of sub-lethal damage due to radiation from different administrations of activity into account. In contrast to the previous formula, the new G-factor has an explicit dependence on the time interval between administrations. The BED of tumour and liver is analysed in MRT of neuroblastoma with (131)I-mIBG, following a common two-administration protocol with a mass-based activity prescription. A BED analysis is also made for modified schedules, when due to local regulations there is a maximum permitted activity for each administration. Modifications include both the simplistic approach of delivering this maximum permitted activity in each of the two administrations, and also the introduction of additional administrations while maintaining the protocol-prescribed total activity. For the cases studied with additional (i.e. more than two) administrations, BED of tumour and liver decreases at most 12% and 29%, respectively. The decrease in BED of the tumour is however modest compared to the two-administration schedule using the maximum permitted activity, where the decrease compared to the original schedule is 47%.
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10.
  • Sjögreen Gleisner, Katarina, et al. (författare)
  • Registration of serial SPECT/CT images for three-dimensional dosimetry in radionuclide therapy.
  • 2009
  • Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 54:20, s. 6181-6200
  • Tidskriftsartikel (refereegranskat)abstract
    • For radionuclide therapy, individual patient pharmacokinetics can be measured in three dimensions by sequential SPECT imaging. Accurate registration of the time series of images is central for voxel-based calculations of the residence time and absorbed dose. In this work, rigid and non-rigid methods are evaluated for registration of 6-7 SPECT/CT images acquired over a week, in anatomical regions from the head-and-neck region down to the pelvis. A method for calculation of the absorbed dose, including a voxel mass determination from the CT images, is also described. Registration of the SPECT/CT images is based on a CT-derived spatial transformation. Evaluation is focused on the CT registration accuracy, and on its impact on values of residence time and absorbed dose. According to the CT evaluation, the non-rigid method produces a more accurate registration than the rigid one. For images of the residence time and absorbed dose, registration produces a sharpening of the images. For volumes-of-interest, the differences between rigid and non-rigid results are generally small. However, the non-rigid method is more consistent for regions where non-rigid patient movements are likely, such as in the head-neck-shoulder region.
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