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| 2. |
- Al-Hallaq, Hania A., et al.
(författare)
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AAPM task group report 302 : Surface-guided radiotherapy
- 2022
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Ingår i: Medical Physics. - : Wiley. - 0094-2405 .- 2473-4209. ; 49:4, s. 82-112
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Tidskriftsartikel (refereegranskat)abstract
- The clinical use of surface imaging has increased dramatically, with demonstrated utility for initial patient positioning, real-time motion monitoring, and beam gating in a variety of anatomical sites. The Therapy Physics Subcommittee and the Imaging for Treatment Verification Working Group of the American Association of Physicists in Medicine commissioned Task Group 302 to review the current clinical uses of surface imaging and emerging clinical applications. The specific charge of this task group was to provide technical guidelines for clinical indications of use for general positioning, breast deep-inspiration breath hold treatment, and frameless stereotactic radiosurgery. Additionally, the task group was charged with providing commissioning and on-going quality assurance (QA) requirements for surface-guided radiation therapy (SGRT) as part of a comprehensive QA program including risk assessment. Workflow considerations for other anatomic sites and for computed tomography simulation, including motion management, are also discussed. Finally, developing clinical applications, such as stereotactic body radiotherapy (SBRT) or proton radiotherapy, are presented. The recommendations made in this report, which are summarized at the end of the report, are applicable to all video-based SGRT systems available at the time of writing.
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| 3. |
- Giantsoudi, D., et al.
(författare)
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A gEUD-based inverse planning technique for HDR prostate brachytherapy : Feasibility study
- 2013
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Ingår i: Medical physics (Lancaster). - : Wiley. - 0094-2405 .- 2473-4209. ; 40:4, s. 041704-
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: The purpose of this work was to study the feasibility of a new inverse planning technique based on the generalized equivalent uniform dose for image-guided high dose rate (HDR) prostate cancer brachytherapy in comparison to conventional dose-volume based optimization. Methods: The quality of 12 clinical HDR brachytherapy implants for prostate utilizing HIPO (Hybrid Inverse Planning Optimization) is compared with alternative plans, which were produced through inverse planning using the generalized equivalent uniform dose (gEUD). All the common dose-volume indices for the prostate and the organs at risk were considered together with radiobiological measures. The clinical effectiveness of the different dose distributions was investigated by comparing dose volume histogram and gEUD evaluators. Results: Our results demonstrate the feasibility of gEUD-based inverse planning in HDR brachytherapy implants for prostate. A statistically significant decrease in D-10 or/and final gEUD values for the organs at risk (urethra, bladder, and rectum) was found while improving dose homogeneity or dose conformity of the target volume. Conclusions: Following the promising results of gEUD-based optimization in intensity modulated radiation therapy treatment optimization, as reported in the literature, the implementation of a similar model in HDR brachytherapy treatment plan optimization is suggested by this study. The potential of improved sparing of organs at risk was shown for various gEUD-based optimization parameter protocols, which indicates the ability of this method to adapt to the user's preferences.
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| 4. |
- Lagerlöf, Jakob Heydorn, 1978, et al.
(författare)
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The impact of including spatially longitudinal heterogeneities of vessel oxygen content and vascular fraction in 3D tumor oxygenation models on predicted radiation sensitivity.
- 2014
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Ingår i: Medical physics. - : Wiley. - 0094-2405 .- 2473-4209. ; 41:4
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen distribution models have been used to analyze the influences of oxygen tensions on tissue response after radiotherapy. These distributions are often generated assuming constant oxygen tension in the blood vessels. However, as red blood cells progress through the vessels, oxygen is continuously released into the plasma and the surrounding tissue, resulting in longitudinally varying oxygen levels in the blood vessels. In the present study, the authors investigated whether a tumor oxygenation model that incorporated longitudinally varying oxygen levels would provide different predictions of necrotic fractions and radiosensitivity compared to commonly used models with a constant oxygen pressure.
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| 5. |
- Morén, Björn, 1987-, et al.
(författare)
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Optimization in treatment planning of high dose‐rate brachytherapy : Review and analysis of mathematical models
- 2021
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Ingår i: Medical Physics. - : Wiley-Blackwell Publishing Inc.. - 2473-4209 .- 0094-2405. ; 48:5, s. 2057-2082
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Forskningsöversikt (refereegranskat)abstract
- Treatment planning in high dose‐rate brachytherapy has traditionally been conducted with manual forward planning, but inverse planning is today increasingly used in clinical practice. There is a large variety of proposed optimization models and algorithms to model and solve the treatment planning problem. Two major parts of inverse treatment planning for which mathematical optimization can be used are the decisions about catheter placement and dwell time distributions. Both these problems as well as integrated approaches are included in this review. The proposed models include linear penalty models, dose–volume models, mean‐tail dose models, quadratic penalty models, radiobiological models, and multiobjective models. The aim of this survey is twofold: (i) to give a broad overview over mathematical optimization models used for treatment planning of brachytherapy and (ii) to provide mathematical analyses and comparisons between models. New technologies for brachytherapy treatments and methods for treatment planning are also discussed. Of particular interest for future research is a thorough comparison between optimization models and algorithms on the same dataset, and clinical validation of proposed optimization approaches with respect to patient outcome.
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| 6. |
- Nyholm, Tufve, et al.
(författare)
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MR and CT data with multiobserver delineations of organs in the pelvic areaPart of the Gold Atlas project
- 2018
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Ingår i: Med Phys. - : Wiley. - 0094-2405 .- 2473-4209. ; 45:3, s. 1295-1300
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Tidskriftsartikel (refereegranskat)abstract
- PurposeWe describe a public dataset with MR and CT images of patients performed in the same position with both multiobserver and expert consensus delineations of relevant organs in the male pelvic region. The purpose was to provide means for training and validation of segmentation algorithms and methods to convert MR to CT like data, i.e., so called synthetic CT (sCT). Acquisition and validation methodsT1- and T2-weighted MR images as well as CT data were collected for 19 patients at three different departments. Five experts delineated nine organs for each patient based on the T2-weighted MR images. An automatic method was used to fuse the delineations. Starting from each fused delineation, a consensus delineation was agreed upon by the five experts for each organ and patient. Segmentation overlap between user delineations with respect to the consensus delineations was measured to describe the spread of the collected data. Finally, an open-source software was used to create deformation vector fields describing the relation between MR and CT images to further increase the usability of the dataset. Data format and usage notesThe dataset has been made publically available to be used for academic purposes, and can be accessed from . Potential applicationsThe dataset provides a useful source for training and validation of segmentation algorithms as well as methods to convert MR to CT-like data (sCT). To give some examples: The T2-weighted MR images with their consensus delineations can directly be used as a template in an existing atlas-based segmentation engine; the expert delineations are useful to validate the performance of a segmentation algorithm as they provide a way to measure variability among users which can be compared with the result of an automatic segmentation; and the pairwise deformably registered MR and CT images can be a source for an atlas-based sCT algorithm or for validation of sCT algorithm. (c) 2018 The Authors. Medical Physics published by Wiley Periodicals, Inc. on behalf of American Association of Physicists in Medicine.
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| 7. |
- Romero-Expósito, Maite, et al.
(författare)
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Range shifter contribution to neutron exposure of patients undergoing proton pencil beam scanning
- 2023
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Ingår i: Medical physics (Lancaster). - 0094-2405.
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Tidskriftsartikel (refereegranskat)abstract
- Background: Superficial targets require the use of the lowest energies within the available energy range in proton pencil-beam scanning (PBS) technique. However, the lower efficiency of the energy selection system at these energies and the requirement of a greater number of layers may represent disadvantages for this approach. The alternative is to use a range shifter (RS) at nozzle exit. However, one of the concerns of using this beamline element is that it becomes an additional source of neutrons that could irradiate organs situated far from the target.Purpose: The purpose of this study is to assess the increase in neutron dose due to the RS in proton PBS technique. Additionally, an analytical model for the neutron production is tested.Methods: Two clinical plans, designed to achieve identical target coverage, were created for an anthropomorphic phantom. These plans consisted of a lateral field delivering an absorbed dose of 60 Gy (RBE) to the target. One of the plans employed the RS. The MCNP code was used to simulate the plans, evaluating the distribution of neutron dose equivalent (Hn) and the equivalent dose in organ. In the plan with the RS plan, neutron production from both the patient and the RS were assessed separately. Hn values were also fitted versus the distance to field edge using a Gaussian function.Results: Hn per prescription dose, in the plan using the RS, ranged between 1.4 and 3.7 mSv/Gy at the field edge, whereas doses at 40 cm from the edge ranged from 9.9 to 32 μSv/Gy. These values are 1.2 to 10 times higher compared to those obtained without the RS. Both this factor and the contribution of neutrons originating from the RS increases with the distance from field edge. A triple-Gaussian function was able to reproduce the equivalent dose in organs within a factor of 2, although underestimating the values.Conclusions: The dose deposited in the patient by the neutrons originating from the RS predominantly affects areas away from the target (beyond approximately 25 cm from field edge), resulting in a neutron dose equivalent of the order of mSv. This indicates an overall low neutron contribution from the use of RS in PBS.
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| 8. |
- Roth, Daniel, et al.
(författare)
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A method for tumor dosimetry based on hybrid planar-SPECT/CT images and semiautomatic segmentation
- 2018
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Ingår i: Medical Physics. - : Wiley. - 0094-2405 .- 2473-4209. ; 45:11, s. 5004-5018
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: A hybrid planar-SPECT/CT method for tumor dosimetry in 177Lu-DOTATATE therapy, applicable to datasets consisting of multiple conjugate-view images and one SPECT/CT, is developed and evaluated. Methods: The imaging protocol includes conjugate-view imaging at 1, 24, 96, and 168 h post infusion (p.i.) and a SPECT/CT acquisition 24 h p.i. The dosimetry method uses the planar images to estimate the shape of the time–activity concentration curve, which is then rescaled to absolute units using the SPECT-derived activity concentration. The resulting time-integrated activity concentration coefficient (TIACC) is used to calculate the tumor-absorbed dose. Semiautomatic segmentation techniques are applied for tumor delineation in both planar and SPECT images, where the planar image segmentation is accomplished using an active-rays-based technique. The selection of tumors is done by visual inspection of planar and SPECT images and applying a set of criteria concerning the tumor visibility and possible interference from superimposed activity uptakes in the planar images. Five different strategies for determining values from planar regions of interest (ROIs), based on entire or partial ROIs, and with and without background correction, are evaluated. Evaluation is performed against a SPECT/CT-based method on data from six patients where sequential conjugate-view and SPECT/CT imaging have been performed in parallel and against ground truths in Monte Carlo simulated images. The patient data are also used to evaluate the interoperator variability and to assess the validity of the developed criteria for tumor selection. Results: For patient images, the hybrid method produces TIACCs that are on average 6% below those of the SPECT/CT only method, with standard deviations for the relative TIACC differences of 8%–11%. Simulations show that the hybrid and SPECT-based methods estimate the TIACCs to within approximately 10% for tumors larger than around 10 ml, while for smaller tumors, all methods underestimate the TIACCs due to underestimations of the activity concentrations in the SPECT images. The planar image segmentation has a low operator dependence, with a median Dice similarity coefficient of 0.97 between operators. The adopted criteria for tumor selection manage to discriminate the tumors for which the absorbed-dose deviations between the hybrid and SPECT methods are the highest. Conclusions: The hybrid method is found suitable for studies of tumor-absorbed doses in radionuclide therapy, provided that selection criteria regarding the visibility and overlapping activities in the planar images are applied.
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| 9. |
- Candela-Juan, C., et al.
(författare)
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Dosimetric characterization of two radium sources for retrospective dosimetry studies
- 2015
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Ingår i: Medical physics (Lancaster). - : American Association of Physicists in Medicine: Medical Physics. - 0094-2405 .- 2473-4209. ; 42:5, s. 2132-2142
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: During the first part of the 20th century, Ra-226 was the most used radionuclide for brachytherapy. Retrospective accurate dosimetry, coupled with patient follow up, is important for advancing knowledge on long-term radiation effects. The purpose of this work was to dosimetrically characterize two Ra-226 sources, commonly used in Sweden during the first half of the 20th century, for retrospective dose-effect studies. Methods: An 8 mg Ra-226 tube and a 10 mg Ra-226 needle, used at Radiumhemmet (Karolinska University Hospital, Stockholm, Sweden), from 1925 to the 1960s, were modeled in two independent Monte Carlo (MC) radiation transport codes: GEANT4 and MCNP5. Absorbed dose and collision kerma around the two sources were obtained, from which the TG-43 parameters were derived for the secular equilibrium state. Furthermore, results from this dosimetric formalism were compared with results from a MC simulation with a superficial mould constituted by five needles inside a glass casing, placed over a water phantom, trying to mimic a typical clinical setup. Calculated absorbed doses using the TG-43 formalism were also compared with previously reported measurements and calculations based on the Sievert integral. Finally, the dose rate at large distances from a Ra-226 point-like-source placed in the center of 1 m radius water sphere was calculated with GEANT4. Results: TG-43 parameters [including gL(r), F(r,theta), Lambda, and s(K)] have been uploaded in spreadsheets as additional material, and the fitting parameters of a mathematical curve that provides the dose rate between 10 and 60 cm from the source have been provided. Results from TG-43 formalism are consistent within the treatment volume with those of a MC simulation of a typical clinical scenario. Comparisons with reported measurements made with thermoluminescent dosimeters show differences up to 13% along the transverse axis of the radium needle. It has been estimated that the uncertainty associated to the absorbed dose within the treatment volume is 10%-15%, whereas uncertainty of absorbed dose to distant organs is roughly 20%-25%. Conclusions: The results provided here facilitate retrospective dosimetry studies of Ra-226 using modern treatment planning systems, which may be used to improve knowledge on long term radiation effects. It is surely important for the epidemiologic studies to be aware of the estimated uncertainty provided here before extracting their conclusions.
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| 10. |
- Tranel, Jonathan, et al.
(författare)
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Technical note: Errors introduced when using Dose Voxel Kernels for estimating absorbed dose from radiopharmaceutical therapies involving alpha emitters
- 2024
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Ingår i: MEDICAL PHYSICS. - 0094-2405 .- 2473-4209.
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Tidskriftsartikel (refereegranskat)abstract
- Background: In radiopharmaceutical therapies (RPT) involving beta emitters, absorbed dose (D-abs) calculations often employ the use of dose voxel kernels (DVK). Such methods are faster and easier to implement than Monte Carlo (MC) simulations. Using DVK methods implies a non-stochastic distribution of particles. This is a valid assumption for betas where thousands to tens of thousands of particles traversing the cell nucleus are required to achieve cell kill. However, alpha particles have linear energy transfers (LET) that are similar to 500 times higher than LETs of betas. This results in a significant probability of killing a cell from even a single traversal through its nucleus. Consequently, the activity used for therapy involving alphas is very low, and the use of DVKs for estimating D-abs will generate results that may be erroneous. Purpose: This work aims at illustrating how use of DVKs affect the resulting D-abs in small tumors when irradiated with clinically relevant amounts of beta- and alpha-emitters. The results are compared with those from using a Monte Carlo method where the energy deposition from individual tracks is simulated. Methods: To illustrate the issues associated with DVK for alpha radiopharmaceutical therapies at the microscale, a tumor cluster model was used to compare beta (Lu-177) and alphas (At-211, Ac-225, and Th-227) irradiations. We used 103 beta particles and 20 alpha particles per cell, which is within the range of the required number of particle traversals through its nucleus to sterilize a cell. Results from using both methods were presented with D-abs histograms, dose volume histograms, and D-abs error maps. Results: For beta-emitter (Lu-177) irradiating the modeled tumor cluster, resulting D-abs was similar for both DVK and MC methods. For all alpha emitters, the use of DVK led to an overestimation of D-abs when compared to results generated using a MC approach. Conclusions: Our results demonstrate that the use of DVK methods for alpha emitters can lead to an overestimation in the calculated D-abs. The use of DVKs for therapies involving alpha emitters may therefore not be appropriate when only referring to the mean D-abs metric.
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