| 5021. |
- Leide Svegborn, Sigrid
(författare)
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External radiation exposure of personnel in nuclear medicine from F-18, Tc-99m and I-131 with special reference to fingers, eyes and thyroid
- 2012
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Ingår i: Radiation Protection Dosimetry. - : Oxford University Press (OUP). - 1742-3406 .- 0144-8420. ; 149:2, s. 196-206
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Tidskriftsartikel (refereegranskat)abstract
- The radiation exposure of fingers, thyroid and eyes of workers handling radiopharmaceuticals during various nuclear medicine procedures was measured using thermoluminescent dosemeters. Dosemeters were placed on the finger tips of 19 workers on several different occasions for various procedures. Additionally, the routinely determined whole-body doses to various groups of workers were analysed. The finger dose measurements demonstrated clear differences between the various tasks, from 0.0012 µGy MBq(-1) (unpacking and installing (99)Mo/(99m)Tc-generator) to 3.0 µGy MBq(-1) (syringe withdrawal, injection and waste handling of (18)F-FDG). As long as the worker was handling (99m)Tc, the dose to the fingers was well below the ICRP dose limits, even when the activity was high. Special concern should, however, be devoted to the handling of (18)F, since the dose to the fingers could easily reach the dose limits. The estimated dose to eyes and thyroid was well below the dose limits. Since the introduction of the positron emission tomography/computed tomography facility, the annual whole-body dose has increased for those directly involved in the handling of (18)F. The annual whole-body dose of 0.2-2.5 mGy was, however, well below the dose limits.
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| 5022. |
- Leide Svegborn, Sigrid
(författare)
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Radiation exposure of patients and personnel from a PET/CT procedure with F-18-FDG
- 2010
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Ingår i: Radiation Protection Dosimetry. - : Oxford University Press (OUP). - 1742-3406 .- 0144-8420. ; 139:1-3, s. 208-213
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Tidskriftsartikel (refereegranskat)abstract
- The positron emission tomography (PET)/computed tomography (CT) camera is a combination of a PET camera and a CT. The image from the PET camera is based on the detection of radiation that is emitted from a radioactive tracer, which has been given to the patient as an intravenous injection. The radiation that is emitted from the radioactive tracer is more energetic than any other radiation used in medical diagnostic procedures and this requires special radiation protection routines. The CT image is based on the detection of radiation produced from an X-ray tube and transmitted through the patient. The radiation exposure of the personnel during the CT procedure is generally very low. Regarding radiation exposure of the patient, it is important to notice whether a CT scan has been performed prior to the PET/CT in order to avoid any unnecessary irradiation. The total effective dose to the patient from a PET/CT procedure is approximately 10 mSv. The major part comes from internal irradiation due to radiopharmaceuticals within the patients (e.g. (18)F-FDG: approximately 6-7 mSv), and a minor part is due to the CT scan (low-dose CT scan: approximately 2-4 mSv). If a full diagnostic CT investigation is performed, the effective dose may be considerably higher. If the patient is pregnant, a PET/CT procedure should be avoided or postponed, unless it is vital for the patient. An interruption in breastfeeding is not necessary after a PET/CT procedure of the nursing mother. Close contact between the patient and a small child should however be avoided for a couple of hours after the administration of the radiopharmaceutical. The radiation dose to the personnel arises mainly due to handling of the radiopharmaceuticals (syringe withdrawal, injection, waste handling, etc.) and from close contact to the patient. This radiation dose can be limited by using the inverse-square law, i.e. by using the fact that the absorbed dose decreases substantially with increasing distance between the radiation source and the personnel.
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| 5023. |
- Leigh, Richard, et al.
(författare)
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Imaging the physiological evolution of the ischemic penumbra in acute ischemic stroke
- 2018
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Ingår i: Journal of Cerebral Blood Flow and Metabolism. - 1559-7016. ; 38:9, s. 1500-1516
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Forskningsöversikt (refereegranskat)abstract
- We review the hemodynamic, metabolic and cellular parameters affected during early ischemia and their changes as a function of approximate cerebral blood flow ( CBF) thresholds. These parameters underlie the current practical definition of an ischemic penumbra, namely metabolically affected but still viable brain tissue. Such tissue is at risk of infarction under continuing conditions of reduced CBF, but can be rescued through timely intervention. This definition will be useful in clinical diagnosis only if imaging techniques exist that can rapidly, and with sufficient accuracy, visualize the existence of a mismatch between such a metabolically affected area and regions that have suffered cell depolarization. Unfortunately, clinical data show that defining the outer boundary of the penumbra based solely on perfusion-related thresholds may not be sufficiently accurate. Also, thresholds for CBF and cerebral blood volume ( CBV) differ for white and gray matter and evolve with time for both inner and outer penumbral boundaries. As such, practical penumbral imaging would involve parameters in which the physiology is immediately displayed in a manner independent of baseline CBF or CBF threshold, namely pH, oxygen extraction fraction ( OEF), diffusion constant and mean transit time ( MTT). Suitable imaging technologies will need to meet this requirement in a 10-20 min exam.
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| 5024. |
- Leinonen, Ville, et al.
(författare)
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Diagnostic effectiveness of quantitative [¹⁸F]flutemetamol PET imaging for detection of fibrillar amyloid β using cortical biopsy histopathology as the standard of truth in subjects with idiopathic normal pressure hydrocephalus.
- 2014
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Ingår i: Acta neuropathologica communications. - : Springer Science and Business Media LLC. - 2051-5960. ; 2, s. 46-
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Tidskriftsartikel (refereegranskat)abstract
- INTRODUCTION: PET imaging of amyloid-β (Aβ) in vivo holds promise for aiding in earlier diagnosis and intervention in Alzheimer's disease (AD) and mild cognitive impairment. AD-like Aβ pathology is a common comorbidity in patients with idiopathic normal pressure hydrocephalus (iNPH). Fifty patients with iNPH needing ventriculo-peritoneal shunting or intracranial pressure monitoring underwent [18F]flutemetamol PET before (N = 28) or after (N = 22) surgery. Cortical uptake of [18F]flutemetamol was assessed visually by blinded reviewers, and also quantitatively via standard uptake value ratio (SUVR) in specific neocortical regions in relation to either cerebellum or pons reference region: the cerebral cortex of (prospective studies) or surrounding (retrospective studies) the biopsy site, the contralateral homolog, and a calculated composite brain measure. Aβ pathology in the biopsy specimen (standard of truth [SoT]) was measured using Bielschowsky silver and thioflavin S plaque scores, percentage area of grey matter positive for monoclonal antibody to Aβ (4G8), and overall pathology impression. We set out to find (1) which pair(s) of PET SUVR and pathology SoT endpoints matched best, (2) whether quantitative measures of [18F]flutemetamol PET were better for predicting the pathology outcome than blinded image examination (BIE), and (3) whether there was a better match between PET image findings in retrospective vs. prospective studies.RESULTS: Of the 24 possible endpoint/SoT combinations, the one with composite-cerebellum SUVR and SoT based on overall pathology had the highest Youden index (1.000), receiver operating characteristic area under the curve (1.000), sensitivity (1.000), specificity (1.000), and sum of sensitivity and specificity for the pooled data as well as for the retrospective and prospective studies separately (2.00, for all 3). The BIE sum of sensitivity and specificity, comparable to that for quantitation, was highest using Bielschowsky silver as SoT for all SUVRs (ipsilateral, contralateral, and composite, for both reference regions). The composite SUVR had a 100% positive predictive value (both reference regions) for the overall pathology diagnosis. All SUVRs had a 100% negative predictive value for the Bielschowsky silver result.CONCLUSION: Bielschowsky silver stain and overall pathology judgment showed the strongest associations with imaging results.
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| 5025. |
- Leinonen, V, et al.
(författare)
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Positron emission tomography with [18F]flutemetamol and [11C]PiB for in vivo detection of cerebral cortical amyloid in normal pressure hydrocephalus patients.
- 2013
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Ingår i: European Journal of Neurology. - : Wiley. - 1351-5101 .- 1468-1331. ; 20:7, s. 1043-52
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND AND PURPOSE: This study determined the correlation between uptake of the amyloid positron emission tomography (PET) imaging agent [(18) F]flutemetamol and amyloid-β measured by immunohistochemical and histochemical staining in a frontal cortical biopsy.METHODS: Fifteen patients with possible normal pressure hydrocephalus (NPH) and previous brain biopsy obtained during intracranial pressure monitoring underwent [18F]flutemetamol PET. Seven of these patients also underwent [11C] Pittsburgh compound B (PiB) PET. [18F]Flutemetamol and [11C]PiB uptake was quantified using standardized uptake value ratio (SUVR) with the cerebellar cortex as a reference region. Tissue amyloid-β was evaluated using the monoclonal antibody 4G8, Thioflavin-S and Bielschowsky silver stain.RESULTS: [18F]Flutemetamol and [11C]PiB SUVRs correlated with biopsy specimen amyloid-β levels contralateral (r = 0.86, P < 0.0001; r = 0.96, P = 0.0008) and ipsilateral (r = 0.82, P = 0.0002; r = 0.87, P = 0.01) to the biopsy site. Association between cortical composite [(18) F]flutemetamol SUVRs and [11C]PiB SUVRs was highly significant (r = 0.97, P = 0.0003).CONCLUSIONS: [18F]Flutemetamol detects brain amyloid-β in vivo with moderate to high sensitivity and high specificity. This agent, therefore, represents a valuable new tool to study and verify the presence of amyloid-β pathology, both in patients with possible NPH and among the wider population.
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| 5026. |
- Leitao, Charles Dahlsson, et al.
(författare)
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Evaluating the Therapeutic Efficacy of Mono- and Bivalent Affibody-Based Fusion Proteins Targeting HER3 in a Pancreatic Cancer Xenograft Model
- 2020
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Ingår i: Pharmaceutics. - : MDPI. - 1999-4923. ; 12:6
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Tidskriftsartikel (refereegranskat)abstract
- Human epidermal growth factor receptor 3 (HER3) has been increasingly scrutinized as a potential drug target since the elucidation of its role in mediating tumor growth and acquired therapy resistance. Affibody molecules are so-called scaffold proteins with favorable biophysical properties, such as a small size for improved tissue penetration and extravasation, thermal and chemical stability, and a high tolerance to modifications. Additionally, affibody molecules are efficiently produced in prokaryotic hosts or by chemical peptide synthesis. We have previously evaluated the biodistribution profiles of five mono- and bivalent anti-HER3 affibody molecules (designated as 3) fused to an albumin-binding domain (designated as A), 3A, 33A, 3A3, A33, and A3, that inhibit ligand-dependent phosphorylation. In the present study, we examined the therapeutic efficacy of the three most promising variants, 3A, 33A, and 3A3, in a direct comparison with the HER3-targeting monoclonal antibody seribantumab (MM-121) in a preclinical BxPC-3 pancreatic cancer model. Xenografted mice were treated with either an affibody construct or MM-121 and the tumor growth was compared to a vehicle group. Receptor occupancy was estimated by positron emission tomography/computed tomography (PET/CT) imaging using a HER3-targeting affibody imaging agent [Ga-68]Ga-(HE)(3)-Z(08698)-NODAGA. The affibody molecules could inhibit ligand-dependent phosphorylation and cell proliferation in vitro and demonstrated tumor growth inhibition in vivo comparable to that of MM-121. PET/CT imaging showed full receptor occupancy for all tested drug candidates. Treatment with 3A and 3A3 affibody constructs was more efficient than with 33A and similar to the anti-HER3 antibody seribantumab, showing that the molecular design of affibody-based therapeutics targeting HER3 in terms of the relative position of functional domains and valency has an impact on therapeutic effect.
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| 5027. |
- Lempart, Michael, et al.
(författare)
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Development of a novel radiotherapy motion phantom using a stepper motor driver circuit and evaluation using optical surface scanning
- 2017
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Ingår i: Australasian Physical and Engineering Sciences in Medicine. - : Springer Science and Business Media LLC. - 0158-9938 .- 1879-5447. ; 40:3, s. 717-727
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Tidskriftsartikel (refereegranskat)abstract
- Abstract: Recent developments in radiotherapy have focused on the management of patient motion during treatment. Studies have shown that significant gains in treatment quality can be made by ‘gating’ certain treatments, simultaneously keeping target coverage, and increasing separation to nearby organs at risk (OAR). Motion phantoms can be used to simulate patient breathing motion and provide the means to perform quality control (QC) and quality assurance (QA) of gating functionality as well as to assess the dosimetric impact of motion on individual patient treatments. The aim of this study was to design and build a motion phantom that accurately reproduces the breathing motion of patients to enable end-to-end gating system quality control of various gating systems as well as patient specific quality assurance. A motion phantom based on a stepper motor driver circuit was designed. The phantom can be programmed with both real patient data from an external gating system and with custom signals. The phantom was programmed and evaluated with patient data and with a square wave signal to be tracked with a Sentinel™ (C-Rad, Uppsala, Sweden) motion monitoring system. Results were compared to the original curves with respect to amplitude and phase. The comparison of patient curve data showed a mean error value of −0.09 mm with a standard deviation of 0.24 mm and a mean absolute error of 0.29 mm. The square wave signals could be reproduced with a mean error value of −0.03 mm, a standard deviation of 0.04 mm and a mean absolute error of 0.13 mm. Breathing curve data acquired from an optical scanning system can be reproduced accurately with the help of the in-house built motion phantom. The phantom can also be programmed to follow user designed curve data. This offers the potential for QC of gating systems and various dosimetric quality control applications. Graphical Abstract: [Figure not available: see fulltext.]
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| 5028. |
- Lempart, M., et al.
(författare)
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Latency Characterization of Gated Radiotherapy Treatment Beams Using a PIN Diode Circuit
- 2016
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Ingår i: IRBM. - : Elsevier BV. - 1959-0318. ; 37:3, s. 144-151
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Tidskriftsartikel (refereegranskat)abstract
- Background: Radiotherapy is based on the premise of accurate dose delivery to target volumes within a patient, while minimizing dose to surrounding tissues. Recent developments in the treatment of breast cancer have focused on “gating” the delivery of the treatment beams to minimize the effect of patient motion during treatment, and increasing separation between the target volume and organs at risk (OAR), such as lung, heart and left anterior descending coronary artery. The basic principle involves rapidly switching the treatment beam on or off depending on the patient breathing cycle. It is therefore important to know the characteristics of gated treatments such as latency. Methods: In this work an electrical PIN diode circuit (EPDC) was designed for quality assurance (QA) purposes to examine beam latency timing properties. Evaluation of the EPDC was performed on a TrueBeam™ (Varian, Palo Alto) linear accelerator and its internal gating system. The EPDC was coupled to a moving stage to simulate a binary pattern with fast beam triggering within predefined limits, the so called “gating window”. Pulses of radiation were measured with the PIN diode and the results were compared to measurements of current produced across the linac target. Processing of the beam pulses and calculation of the latency timings was performed by an Atmega328P microcontroller. Results: For beam-on latencies, 2.11 ms (6 MV) and 2.12 ms (10 MV) were measured using the PIN diode, compared to 2.13 ms (6 MV) and 2.15 ms (10 MV) using the target current signal. For beam-off latencies, 57.69 ms (6 MV) and 57.73 ms (10 MV) were measured using the PIN diode, compared to 57.33 ms (6 MV) and 56.01 ms (10 MV) using the target current. Conclusions: PIN diodes can be used for accurate determination of the beam-on and beam-off latency characteristics, which could potentially lead to improvements in gated radiotherapy treatments, for example optimizing the gating windows and in estimating dosimetric errors associated with treatment beam latencies.
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| 5029. |
- Lempart, Michael, et al.
(författare)
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Pelvic U-Net : multi-label semantic segmentation of pelvic organs at risk for radiation therapy anal cancer patients using a deeply supervised shuffle attention convolutional neural network
- 2022
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Ingår i: Radiation Oncology. - : Springer Science and Business Media LLC. - 1748-717X. ; 17:1
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Tidskriftsartikel (refereegranskat)abstract
- Background: Delineation of organs at risk (OAR) for anal cancer radiation therapy treatment planning is a manual and time-consuming process. Deep learning-based methods can accelerate and partially automate this task. The aim of this study was to develop and evaluate a deep learning model for automated and improved segmentations of OAR in the pelvic region. Methods: A 3D, deeply supervised U-Net architecture with shuffle attention, referred to as Pelvic U-Net, was trained on 143 computed tomography (CT) volumes, to segment OAR in the pelvic region, such as total bone marrow, rectum, bladder, and bowel structures. Model predictions were evaluated on an independent test dataset (n = 15) using the Dice similarity coefficient (DSC), the 95th percentile of the Hausdorff distance (HD95), and the mean surface distance (MSD). In addition, three experienced radiation oncologists rated model predictions on a scale between 1–4 (excellent, good, acceptable, not acceptable). Model performance was also evaluated with respect to segmentation time, by comparing complete manual delineation time against model prediction time without and with manual correction of the predictions. Furthermore, dosimetric implications to treatment plans were evaluated using different dose-volume histogram (DVH) indices. Results: Without any manual corrections, mean DSC values of 97%, 87% and 94% were found for total bone marrow, rectum, and bladder. Mean DSC values for bowel cavity, all bowel, small bowel, and large bowel were 95%, 91%, 87% and 81%, respectively. Total bone marrow, bladder, and bowel cavity segmentations derived from our model were rated excellent (89%, 93%, 42%), good (9%, 5%, 42%), or acceptable (2%, 2%, 16%) on average. For almost all the evaluated DVH indices, no significant difference between model predictions and manual delineations was found. Delineation time per patient could be reduced from 40 to 12 min, including manual corrections of model predictions, and to 4 min without corrections. Conclusions: Our Pelvic U-Net led to credible and clinically applicable OAR segmentations and showed improved performance compared to previous studies. Even though manual adjustments were needed for some predicted structures, segmentation time could be reduced by 70% on average. This allows for an accelerated radiation therapy treatment planning workflow for anal cancer patients.
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| 5030. |
- Lenfeldt, Niklas, et al.
(författare)
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Cerebrospinal fluid pulse pressure method: a possible substitute for the examination of B waves
- 2004
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Ingår i: Journal of Neurosurgery. - : American Association of Neurological Surgeons. - 0022-3085 .- 1933-0693. ; 101:6, s. 944-950
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Tidskriftsartikel (refereegranskat)abstract
- Object. The appearance of numerous B waves during intracranial pressure (ICP) registration in patients with idiopathic adult hydrocephalus syndrome (IAHS) is considered to predict good outcome after shunt surgery. The aim of this study was to describe which physical parameters of the cerebrospinal fluid (CSF) system B-waves reflect and to find a method that could replace long-term B-wave analysis.Methods. Ten patients with IAHS were subjected to long-term registration of ICP and a lumbar constant-pressure infusion test. The B-wave presence, CSF outflow resistance (Rout), and relative pulse pressure coefficient (RPPC) were assessed using computerized analysis. The RPPC was introduced as a parameter reflecting the joint effect of elastance and pulsatory volume changes on ICP and was determined by relating ICP pulse amplitudes to mean ICP.Conclusions. The B-wave presence on ICP registration correlates strongly with RPPC (r = 0.91, p < 0.001, 10 patients) but not with CSF Rout. This correlation indicates that B waves—like RPPC—primarily reflect the ability of the CSF system to reallocate and store liquid rather than absorb it. The RPPC-assessing lumbar short-term CSF pulse pressure method could replace the intracranial long-term B-wave analysis.
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