| 1. |
- Omar, A., et al.
(författare)
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A framework for organ dose estimation in x-ray angiography and interventional radiology based on dose-related data in DICOM structured reports
- 2016
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Ingår i: Physics in Medicine and Biology. - Stockholm : Institute of Physics Publishing (IOPP). - 0031-9155 .- 1361-6560. ; 61:8, s. 3063-3083
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Tidskriftsartikel (refereegranskat)abstract
- Although interventional x-ray angiography (XA) procedures involve relatively high radiation doses that can lead to deterministic tissue reactions in addition to stochastic effects, convenient and accurate estimation of absorbed organ doses has traditionally been out of reach. This has mainly been due to the absence of practical means to access dose-related data that describe the physical context of the numerous exposures during an XA procedure. The present work provides a comprehensive and general framework for the determination of absorbed organ dose, based on non-proprietary access to dose-related data by utilizing widely available DICOM radiation dose structured reports. The framework comprises a straightforward calculation workflow to determine the incident kerma and reconstruction of the geometrical relation between the projected x-ray beam and the patient's anatomy. The latter is difficult in practice, as the position of the patient on the table top is unknown. A novel patient-specific approach for reconstruction of the patient position on the table is presented. The proposed approach was evaluated for 150 patients by comparing the estimated position of the primary irradiated organs (the target organs) with their position in clinical DICOM images. The approach is shown to locate the target organ position with a mean (max) deviation of 1.3 (4.3), 1.8 (3.6) and 1.4 (2.9) cm for neurovascular, adult and paediatric cardiovascular procedures, respectively. To illustrate the utility of the framework for systematic and automated organ dose estimation in routine clinical practice, a prototype implementation of the framework with Monte Carlo simulations is included.
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| 2. |
- Kallioniemi, Antti, et al.
(författare)
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Contrast agent enhanced pQCT of articular cartilage.
- 2007
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Ingår i: Physics in Medicine and Biology. - : Institute of Physics Publishing (IOPP). - 0031-9155 .- 1361-6560. ; 52:4, s. 1209-1219
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Tidskriftsartikel (refereegranskat)abstract
- The delayed gadolinium enhanced MRI of cartilage (dGEMRIC) technique is the only non-invasive means to estimate proteoglycan (PG) content in articular cartilage. In dGEMRIC, the anionic paramagnetic contrast agent gadopentetate distributes in inverse relation to negatively charged PGs, leading to a linear relation between T1,Gd and spatial PG content in tissue. In the present study, for the first time, contrast agent enhanced peripheral quantitative computed tomography (pQCT) was applied, analogously to dGEMRIC, for the quantitative detection of spatial PG content in cartilage. The suitability of two anionic radiographic contrast agents, gadopentetate and ioxaglate, to detect enzymatically induced PG depletion in articular cartilage was investigated. First, the interrelationships of x-ray absorption, as measured with pQCT, and the contrast agent solution concentration were investigated. Optimal contrast agent concentrations for the following experiments were selected. Second, diffusion rates for both contrast agents were investigated in intact (n=3) and trypsin-degraded (n=3) bovine patellar cartilage. The contrast agent concentration of the cartilaginous layer was measured prior to and 2-27 h after immersion. Optimal immersion time for the further experiments was selected. Third, the suitability of gadopentetate and ioxaglate enhanced pQCT to detect the enzymatically induced specific PG depletion was investigated by determining the contrast agent concentrations and uronic acid and water contents in digested and intact osteochondral samples (n=16). After trypsin-induced PG loss (-70%, p<0.05) the penetration of gadopentetate and ioxaglate increased (p<0.05) by 34% and 48%, respectively. Gadopentetate and ioxaglate concentrations both showed strong correlation (r=-0.95, r=-0.94, p<0.01, respectively) with the uronic acid content. To conclude, contrast agent enhanced pQCT provides a technique to quantify PG content in normal and experimentally degraded articular cartilage in vitro. As high resolution imaging of e.g. the knee joint is possible with pQCT, the present technique may be further developed for in vivo quantification of PG depletion in osteoarthritic cartilage. However, careful in vitro and in vivo characterization of diffusion mechanics and optimal contrast agent concentrations are needed before diagnostic applications are feasible.
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| 3. |
- Liamsuwan, Thiansin, et al.
(författare)
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A Monte Carlo track structure simulation code for the full-slowing-down carbon projectiles of energies 1 keV u-1–10 MeV u-1 in water
- 2013
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 58:3, s. 673-702
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Tidskriftsartikel (refereegranskat)abstract
- The paper presents a new Monte Carlo track structure code (KURBUC_carbon) for simulations of full slowing down carbon projectiles C0–C6+ of energies 1 keV/u–10 MeV/u in water vapour. The code facilitates investigation of spatial resolution effect for scoring track parameters under the Bragg peak of carbon ion beam. Interactions of carbon projectiles and secondary electrons were followed event-by-event down to 1 keV/u cutoff for primary ions, and down to 10 eV for electrons. Electronic interactions and nuclear elastic scattering were taken into account, including charge exchange reactions and double electronic interactions for the carbon projectiles. The reliability of the code was tested for radial dose, range, and W-value. The calculated results were compared with the published experimental data, and other model calculations. The results obtained showed good agreement in most cases where comparisons could be made. Depth dose profiles for 1-10 MeV/u C6+ were used to form an SOBP of 0.35 mm width in water. At all depths of the SOBP, the energy distributions of the carbon projectiles varied appreciably with the change in the scoring volume. The corresponding variation was nearly negligible for the track average LET, except at the distal end of the SOBP. By varying the scoring slab thickness from 1 to 100 µm, the maximum track average LET decreased by ~30%. The Monte Carlo track structure simulation in the full slowing down mode is a powerful tool for investigation of biophysical properties of radiation tracks under the Bragg peak and SOBP of carbon ion beam. For estimation of radiation effectiveness under the Bragg peak the new Monte Carlo track structure code provides yet another accurate and effective dosimetry tool at a single cell level. This is because radiobiology within tissue elements can only be understood with dosimetry at cellular and subcellular level.
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| 4. |
- Liamsuwan, Thiansin, et al.
(författare)
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Cross sections for bare and dressed carbon ions in water and neon
- 2013
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 58, s. 641-672
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Tidskriftsartikel (refereegranskat)abstract
- The paper presents calculated cross sections for bare and dressed carbon projectiles of charge states q (0 to 6) with energies 1–104 keV/u impacting on molecular water and atomic neon targets. The cross sections of water are of interest for radiobiological studies, but there are very few experimental data for water in any phase or non-existent. The more extensive experimental database for the neon target made it possible to test the reliability of the model calculations for many-electron collision system. The current calculations cover major single and double electronic interactions of low and intermediate energy carbon projectiles. The three-body classical trajectory Monte Carlo (CTMC) method was used for the calculation of one-electron transition probabilities for target ionisation, electron capture, and projectile electron loss. The many-electron problem was taken into account using statistical methods: a modified independent event model was used for pure (direct) and simultaneous target and projectile ionisations; and the independent particle model for pure electron capture and electron capture accompanied by target ionisation. Results are presented for double differential cross sections (DDCS) for total electron emission by carbon projectile impact on neon. For the water target, we present: single differential cross sections (SDCS) and DDCS for single target ionisation; total cross sections (TCS) for electron emission; TCS for the pure single electronic interactions; equilibrium charge state fractions; and stopping cross sections. The results were found to be in satisfactory agreement with the experimental data in many cases, including DDCS and SDCS for the single target ionisation, TCS for the total electron emission, and TCS for the pure single electron capture. The stopping cross sections of this work are consistent with the other model calculations for projectile energies ≥800 keV/u, but smaller than the other calculations at lower energies. The discrepancy arises from the inclusion of all carbon charge states and coupling between electron capture and target ionisation channels, while other models use an average projectile charge. The CTMC model presented here provides a tool for cross section calculations for low and intermediate energy carbon projectiles. The calculated cross sections are required for Monte Carlo track structure simulations of full-slowing-down tracks of carbon ions. The work paves the way for biophysical studies and dosimetry at the cellular and subcellular levels in the Bragg peak area of therapeutic carbon ion beam.
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| 5. |
- Miettinen, Kaisa, 1965-, et al.
(författare)
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Interactive Multiobjective Optimization for Anatomy based Three-Dimensinal HDR Brachytherapy
- 2010
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Ingår i: Physics in Medicine and Biology. - : Institute of Physics and Engineering in Medicine. - 0031-9155 .- 1361-6560. ; 55:16, s. 4703-4719
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we present an anatomy-based three-dimensional dose optimization approach for HDR brachytherapy using interactive multiobjective optimization (IMOO). In brachytherapy, the goals are to irradiate a tumor without causing damage to healthy tissue. These goals are often conflicting, i.e. when one target is optimized the other will suffer, and the solution is a compromise between them. IMOO is capable of handling multiple and strongly conflicting objectives in a convenient way. With the IMOO approach, a treatment planner’s knowledge is used to direct the optimization process. Thus, the weaknesses of widely used optimization techniques (e.g. defining weights, computational burden and trial-and-error planning) can be avoided, planning times can be shortened and the number of solutions to be calculated is small. Further, plan quality can be improved by finding advantageous trade-offs between the solutions. In addition, our approach offers an easy way to navigate among the obtained Pareto optimal solutions (i.e. different treatment plans). When considering a simulation model of clinical 3D HDR brachytherapy, the number of variables is significantly smaller compared to IMRT, for example. Thus, when solving the model, the CPU time is relatively short. This makes it possible to exploit IMOO to solve a 3D HDR brachytherapy optimization problem. To demonstrate the advantages of IMOO, two clinical examples of optimizing a gynecologic cervix cancer treatment plan are presented.
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| 6. |
- Ahlgren, L, et al.
(författare)
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Induced activity in a high-energy linear accelerator
- 1988
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 33:3, s. 4-351
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Tidskriftsartikel (refereegranskat)abstract
- Activation products which contribute significantly to the exposure of the staff operating the accelerator were found in the accelerator head in the transparent holder for the lead blocks and in the 60 degrees wedge filter made of lead. A proper choice of material in these parts of the accelerator could easily reduce this exposure without excessive changes in the construction. The absorbed dose-rate level should always be checked before maintenance is carried out inside the accelerator head.
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| 7. |
- Akkurt, I, et al.
(författare)
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Photoneutron yields from tungsten in the energy range of the giant dipole resonance
- 2003
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 48:20, s. 3345-3352
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Tidskriftsartikel (refereegranskat)abstract
- Photoneutron production on the nuclei of high-Z components of medical accelerator heads can lead to a significant secondary dose during a course of bremsstrahlung radiotherapy, However, a quantitative evaluation of secondary neutron dose requires improved data on the photoreaction yields. These have been measured as a function of photon energy, neutron energy and neutron angle for W-nat, using tagged photons at the MAX-Lab photonuclear facility in Sweden. This work presents neutron yields for W-nat(gamma, n) and compares these with the predictions of the Monte Carlo code MCNP-GN, developed specifically to simulate photoneutron production at medical accelerators.
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| 8. |
- Andersson-Engels, Stefan, et al.
(författare)
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In vivo fluorescence imaging for tissue diagnostics
- 1997
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 42:5, s. 815-824
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Tidskriftsartikel (refereegranskat)abstract
- Non-invasive fluorescence imaging has the potential to provide in vivo diagnostic information for many clinical specialities. Techniques have been developed over the years for simple ocular observations following UV excitation to sophisticated spectroscopic imaging using advanced equipment. Much of the impetus for research on fluorescence imaging for tissue diagnostics has come from parallel developments in photodynamic therapy of malignant lesions with fluorescent photosensitizers. However, the fluorescence of endogenous molecules (tissue autofluorescence) also plays an important role in most applications. In this paper, the possibilities of imaging tissues using fluorescence spectroscopy as a mean of tissue characterization are discussed. The various imaging techniques for extracting diagnostic information suggested in the literature are reviewed. The development of exogenous fluorophores for this purpose is also presented. Finally, the present status of clinical evaluation and future directions are discussed.
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| 9. |
- Andersson, Martin, et al.
(författare)
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Improved estimates of the radiation absorbed dose to the urinary bladder wall
- 2014
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Ingår i: Physics in Medicine and Biology. - : Institute of Physics Publishing (IOPP). - 0031-9155 .- 1361-6560. ; 59:9, s. 2173-2182
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Tidskriftsartikel (refereegranskat)abstract
- Specific absorbed fractions (SAFs) have been calculated as a function of the content in the urinary bladder in order to allow more realistic calculations of the absorbed dose to the bladder wall. The SAFs were calculated using the urinary bladder anatomy from the ICRP male and female adult reference computational phantoms. The urinary bladder and its content were approximated by a sphere with a wall of constant mass, where the thickness of the wall depended on the amount of urine in the bladder. SAFs were calculated for males and females with 17 different urinary bladder volumes from 10 to 800 mL, using the Monte Carlo computer program MCNP5, at 25 energies of mono-energetic photons and electrons ranging from 10 KeV to 10 MeV. The decay was assumed to be homogeneously distributed in the urinary bladder content and the urinary bladder wall, and the mean absorbed dose to the urinary bladder wall was calculated. The Monte Carlo simulations were validated against measurements made with thermoluminescent dosimeters. The SAFs obtained for a urine volume of 200 mL were compared to the values calculated for the urinary bladder wall using the adult reference computational phantoms. The mean absorbed dose to the urinary wall from F-18-FDG was found to be 77 mu Gy/MBq formales and 86 mu Gy/MBq for females, while for (99)mTc-DTPA the mean absorbed doses were 80 mu Gy/MBq for males and 86 mu Gy/MBq for females. Compared to calculations using a constant value of the SAF from the adult reference computational phantoms, the mean absorbed doses to the bladder wall were 60% higher for F-18-FDG and 30% higher for (99)mTc-DTPA using the new SAFs.
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| 10. |
- Arlig, A, et al.
(författare)
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Attenuation correction in quantitative SPECT of cerebral blood flow: a Monte Carlo study
- 2000
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 45:12, s. 3847-3859
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Tidskriftsartikel (refereegranskat)abstract
- Monte Carlo simulation has been used to produce projections from a voxel-based brain phantom, simulating a 99mTc-HMPAO single photon emission computed tomography (SPECT) brain investigation. For comparison, projections free from the effects of attenuation and scattering were also simulated, giving ideal transaxial images after reconstruction. Three methods of attenuation correction were studied: (a) a pre-processing method, (b) a post-processing uniform method and (c) a post-processing non-uniform method using a density map. The accuracy of these methods was estimated by comparison of the reconstructed images with the ideal images using the normalized mean square error, NMSE, and quantitative values of the regional cerebral blood flow, rCBF. A minimum NMSE was achieved for the effective linear attenuation coefficient mu(eff) = 0.07 (0.09) cm(-1) for the uniform(pre) method, the effective mass attenuation coefficient mu(eff)/rho = 0.08 (0.10) cm2 g(-1) for the uniform(post) method and mu(eff)/rho = 0.12 (0.13) cm2 g(-1) for the non-uniform(post) method. Values in parentheses represent the case of dual-window scatter correction. The non-uniform(post) method performed better, as measured by the NMSE, both with and without scatter correction. Furthermore, the non-uniform(post) method gave, on average, more accurate rCBF values. Although the difference in rCBF accuracy was small between the various methods, the same method should be used for patient studies as for the reference material.
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