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The influence of dopants on thermoluminescence of Sr2MgSi2O7
摘要： We report the influence of dopants on the thermoluminescence of Sr2MgSi2O7. Samples studied comprise undoped Sr2MgSi2O7 and doped versions, namely, Sr2MgSi2O7:Dy3+, Sr2MgSi2O7:Eu3+, Sr2MgSi2O7:Tb3+ and Sr2MgSi2O7:Tb3+,Eu3+ phosphors. All samples show a broad glow peak near 60oC when measured at 1 °C/s after irradiation to 10 Gy. The peak changes with partial heating, irradiation and fades between irradiation and measurement in a manner expected of a composite one. The behaviour is used to exemplify the analysis of a composite peak on the basis that particular features reflect those of the dominant component.
关键词： dose response,thermoluminescence,glow curve,phosphor
更新于2025-09-04 15:30:14
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On the instantaneous dose rate and angular dependence of monolithic silicon array detectors
摘要： The use of small radiation fields characterized by very steep dose gradients is common in modulated arc x-ray radiotherapy. Dosimeters for quality assurance applications would ideally have sensitive volumes relatively small with respect to the field, along with negligible instantaneous dose rate and angular dependence. Silicon-based dosimeters can be fabricated with sensitive volumes < 100 μm across, provide a stable and near energy-independent response in megavoltage photon beams, along with a good linearity with accumulated dose and real-time read-out. However, their sensitivity is instantaneous dose rate and angular dependent. Monolithic silicon array detectors with sufficiently small sensitive volumes and pitch are suitable for high-resolution 2D dose mapping in radiation fields with steep dose gradients. The Octa is a 2D monolithic silicon array detector. It has 512 diode-sensitive volumes arranged with a sub-millimeter pitch. The physical characteristics of the substrate on which it is based, in terms of resistivity and defects concentration, strongly affect its performance. We report on the experimental characterization of two versions of the Octa, manufactured on a bulk and on an epitaxial substrate respectively. Their performance is compared and discussed in terms of their instantaneous dose rate and angular dependence in the context of quality assurance applications in small radiation fields delivered with modulated arc radiotherapy.
关键词： small-field dosimetry,angular dependence,instantaneous dose rate dependence,2D monolithic silicon array detector
更新于2025-09-04 15:30:14
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Surface scanning for 3D dose calculation in intraoperative electron radiation therapy
摘要： Dose calculations in intraoperative electron radiation therapy (IOERT) rely on the conventional assumption of water-equivalent tissues at the applicator end, which defines a flat irradiation surface. However, the shape of the irradiation surface modifies the dose distribution. Our study explores, for the first time, the use of surface scanning methods for three-dimensional dose calculation of IOERT. Two different three-dimensional scanning technologies were evaluated in a simulated IOERT scenario: a tracked conoscopic holography sensor (ConoProbe) and a structured-light three-dimensional scanner (Artec). Dose distributions obtained from computed tomography studies of the surgical field (gold standard) were compared with those calculated under the conventional assumption or from pseudo-computed tomography studies based on surfaces. In the simulated IOERT scenario, the conventional assumption led to an average gamma pass rate of 39.9% for dose values greater than 10% (two configurations, with and without blood in the surgical field). Results improved when considering surfaces in the dose calculation (88.5% for ConoProbe and 92.9% for Artec). More accurate three-dimensional dose distributions were obtained when considering surfaces in the dose calculation of the simulated surgical field. The structured-light three-dimensional scanner provided the best results in terms of dose distributions. The findings obtained in this specific experimental setup warrant further research on surface scanning in the IOERT context owing to the clinical interest of improving the documentation of the actual IOERT scenario.
关键词： Intraoperative radiotherapy,Structured-light 3D scanner,IOERT,Dose distribution,Surface scanning,Conoscopic holography
更新于2025-09-04 15:30:14
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Quantitative Analysis of <sup>18</sup> F-PF-06684511, a Novel PET Radioligand for Selective β-secretase 1 Imaging, in Non-human Primate Brain
摘要： Beta-secretase 1 (BACE1) is a key enzyme in the generation of beta-amyloid, which is accumulated in the brain of Alzheimer’s disease (AD) patients. PF-06684511 was identified as a candidate PET ligand for imaging BACE1 in the brain, and showed high specific binding in an initial assessment in a non-human primate (NHP) PET study utilizing 18F-PF-06684511. In this effort, we aimed to quantitatively evaluate the regional brain distribution of 18F-PF-06684511 in NHPs under baseline and blocking conditions as well as assess the target occupancy of BACE1 inhibitors. In addition, NHP whole body PET measurements were performed to estimate the effective radiation dose. Methods: Initial brain PET measurements were performed at baseline and after oral administration of 5 mg/kg of LY2886721, a BACE1 inhibitor, in two cynomolgus monkeys. Kinetic analysis was performed with the radiometabolite-corrected plasma input function. In addition, a wide dose range of another BACE1 inhibitor, PF-06663195, was examined to investigate the relationship between the brain target occupancy and plasma concentration of the drug. Finally, the effective radiation dose of 18F-PF-06684511 was estimated based on the whole body PET measurements in NHPs. Results: Radiolabeling was accomplished successfully with an incorporation radiochemical yield of 4-12% (decay corrected) from fluorine-18 ion. The radiochemical purity was greater than 99%. The whole brain uptake of 18F-PF-06684511 reached peak (approximately 220%SUV) at approximately 20 minutes and decreased thereafter (approximately 100%SUV at 180 minutes). Two-tissue compartment model described the time activity curves well. Pre-treatment with LY2886721 reduced the total distribution volume of 18F-PF-06684511 by 48 – 80% depending on the brain regions, confirming its in vivo specificity. BACE1 occupancy of PF-06663195, estimated using Lassen occupancy plot, showed a dose-dependent increase. The effective dose of 18F-PF-06684511 was 0.043 mSv/MBq for humans. Conclusion: 18F-PF-06684511 is the first successful PET radioligand for BACE1 brain imaging that demonstrates favorable in vivo binding and brain kinetics in NHPs. (306/350 words)
关键词： PET,brain,BACE1,occupancy,radiation dose,non-human primate
更新于2025-09-04 15:30:14
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Fabrication of high fill-factor aspheric microlens array by dose-modulated lithography and low temperature thermal reflow
摘要： A cost-effective fabrication method for high quality and high fill-factor aspheric microlens arrays (MLAs) is developed. In this method, the complex shape of aspheric microlens is pre-modeled via dose modulation in a digital micromirror device (DMD) based maskless projection lithography system. Digital masks for several bottom layers are replaced from circle to hexagon for the purpose of enhancing the fill-factor of MLAs, then a low temperature thermal reflow process is conducted, after which the average surface roughness of microlens is improved to * 0.427 nm while the pre-modeled profile keeps unchanged. Experimental results show that the fabricated aspheric MLAs have almost 100% fill-factor, high shape accuracy and high surface quality. The presented method may provide a promising approach for rapidly fabricating high quality and high fill-factor aspheric microlens in a simple and low-cost way.
关键词： high fill-factor,dose-modulated lithography,aspheric microlens arrays,surface roughness,low temperature thermal reflow
更新于2025-09-04 15:30:14
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Absorbed doses in salivary and thyroid glands from panoramic radiography and cone beam computed tomography
摘要： Introduction: Panoramic radiography and cone beam computed tomography (CBCT) are very important in the diagnosis of oral diseases, however patients are exposed to the risk of ionizing radiation. This paper describes our study aimed at comparing absorbed doses in the salivary glands and thyroid due to panoramic radiography and CBCT and estimating radiation induced cancer risk associated with those methods. Methods: Absorbed doses of two CBCT equipment (i?CAT? Next Generation and SCANORA? 3D) and a digital panoramic device (ORTHOPANTOMOGRAPH? OP200D) were measured using thermoluminescent dosimeters loaded in an anthropomorphic phantom on sublingual, submandibular, parotid and thyroid glands. Results: Absorbed doses in the i?CAT? device ranged between 0.02 (+/?0.01) and 2.23 mGy (+/?0.03), in the SCANORA? device ranged from 0.01 (+/?0.01) to 2.96 mGy (+/?0.29) and in the ORTHOPANTOMOGRAPH? OP200D ranged between 0.04 mGy and 0.78 mGy. The radiation induced cancer risk was highlighted in the salivary glands, which received higher doses. The protocols that offer the highest risk of cancer are the high resolution protocols of CBCT equipment. Conclusion: CBCT exposes patients to higher levels of radiation than panoramic radiography, so the risks and benefits of each method should be considered. The doses in CBCT were dependent on equipment and exposure parameters, therefore adequate selection minimizes the radiation dose.
关键词： Radiation dose,Cone beam computed tomography,Thermoluminescent dosimetry,Panoramic radiograph
更新于2025-09-04 15:30:14
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Organ doses evaluation for chest computed tomography procedures with TL dosimeters: Comparison with Monte Carlo simulations
摘要： Purpose: To evaluate organ doses in routine and low‐dose chest computed tomography (CT) protocols using an experimental methodology. To compare experimental results with results obtained by the National Cancer Institute dosimetry system for CT (NCICT) organ dose calculator. To address the differences on organ dose measurements using tube current modulation (TCM) and fixed tube current protocols. Methods: An experimental approach to evaluate organ doses in pediatric and adult anthropomorphic phantoms using thermoluminescent dosimeters (TLDs) was employed in this study. Several analyses were performed in order to establish the best way to achieve the main results in this investigation. The protocols used in this study were selected after an analysis of patient data collected from the Institute of Radiology of the School of Medicine of the University of S?o Paulo (InRad). The image quality was evaluated by a radiologist from this institution. Six chest adult protocols and four chest pediatric protocols were evaluated. Lung doses were evaluated for the adult phantom and lung and thyroid doses were evaluated for the pediatric phantom. The irradiations were performed using both a GE and a Philips CT scanner. Finally, organ doses measured with dosimeters were compared with Monte Carlo simulations performed with NCICT. Results: After analyzing the data collected from all CT examinations performed during a period of 3 yr, the authors identified that adult and pediatric chest CT are among the most applied protocol in patients in that clinical institution, demonstrating the relevance on evaluating organ doses due to these examinations. With regards to the scan parameters adopted, the authors identified that using 80 kV instead of 120 kV for a pediatric chest routine CT, with TCM in both situations, can lead up to a 28.7% decrease on the absorbed dose. Moreover, in comparison to the standard adult protocol, which is performed with fixed mAs, TCM, and ultra low‐dose protocols resulted in dose reductions of up to 35.0% and 90.0%, respectively. Finally, the percent differences found between experimental and Monte Carlo simulated organ doses were within a 20% interval. Conclusions: The results obtained in this study measured the impact on the absorbed dose in routine chest CT by changing several scan parameters while the image quality could be potentially preserved.
关键词： Monte Carlo simulations,computed tomography,dosimetry/exposure assessment,organ dose,image quality
更新于2025-09-04 15:30:14
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Dose reconstruction from PET images in carbon ion therapy: a deconvolution approach
摘要： Dose and range verification have become important tools to bring carbon ion therapy to a higher level of confidence in clinical applications. Positron emission tomography is among the most commonly used approaches for this purpose and relies on the creation of positron emitting nuclei in nuclear interactions of the primary ions with tissue. Predictions of these positron emitter distributions are usually obtained from time-consuming Monte Carlo simulations or measurements from previous treatment fractions, and their comparison to the current, measured image allows for treatment verification. Still, a direct comparison of planned and delivered dose would be highly desirable, since the dose is the quantity of interest in radiation therapy and its confirmation improves quality assurance in carbon ion therapy. In this work, we present a deconvolution approach to predict dose distributions from PET images in carbon ion therapy. Under the assumption that the one-dimensional PET distribution is described by a convolution of the depth dose distribution and a filter kernel, an evolutionary algorithm is introduced to perform the reverse step and predict the depth dose distribution from a measured PET distribution. Filter kernels are obtained from either a library or are created for any given situation on-the-fly, using predictions of the β+-decay and depth dose distributions, and the very same evolutionary algorithm. The applicability of this approach is demonstrated for monoenergetic and polyenergetic carbon ion irradiation of homogeneous and heterogeneous solid phantoms as well as a patient computed tomography image, using Monte Carlo simulated distributions and measured in-beam PET data. Carbon ion ranges are predicted within less than 0.5 mm and 1 mm deviation for simulated and measured distributions, respectively.
关键词： evolutionary algorithm,PET imaging,range verification,carbon ion therapy,dose reconstruction
更新于2025-09-04 15:30:14
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A two-year study of diffused retinal pigment epitheliopathy treated with half-dose photodynamic therapy guided by simultaneous angiography and optical coherence tomography
摘要： Objectives Diffused retinal pigment epitheliopathy (DRPE) is not necessarily the same as chronic central serous chorioretinopathy (CSC), but a severe subgroup under the umbrella of chronic CSC. This study was to evaluate the efficacy and safety of half-dose PDT treating DRPE. Methods A retrospective case series design was used. Forty-eight consecutive patients (48 eyes) with DRPE treated with half-dose PDT underwent follow-up at baseline, 3 months, 6 months, 12 months and 24 months. Simultaneous FA, ICGA and OCT were used for the treatment and follow-up. The primary outcomes were the subretinal fluid and best-corrected visual acuity in optical coherence tomography. Results Complete fluid absorption was achieved in 95.8% of eyes at 3 months and 100.0% of eyes at 24 months. The baseline logarithm of the minimum angle of resolution (logMAR) BCVA, which was 0.51 ± 0.36, significantly improved to 0.43 ± 0.38 (p < 0.001) at 6 months. The boost continued to 0.29 ± 0.37 (p < 0.001) at 12 months and 0.19 ± 0.39 (p < 0.001) at 24 months. The integrities of the ellipsoid zone (EZ) and interdigitation zone (IZ) improved throughout. Regression analyses showed the BCVA in logMAR was inversely correlated with the EZ (p < 0.01) and IZ (p < 0.01). The recurrence rate was 6.3%. No severe complications were witnessed. Conclusions In 48 eyes with DRPE, simultaneous angiography and OCT facilitated a more comprehensive guidance for half-dose PDT treatment and follow-up. The BCVA improvement occurred at 6 months, which may be attributed to the restoration of the outer retinal structure.
关键词： chronic central serous chorioretinopathy,half-dose photodynamic therapy,Diffused retinal pigment epitheliopathy,angiography,CSC,optical coherence tomography,OCT,DRPE,PDT
更新于2025-09-04 15:30:14
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Feasibility Study of Patient Specific Quality Assurance Using Transit Dosimetry Based on Measurement with an Electronic Portal Imaging Device
摘要： This study was designed to measure transit dose with an electronic portal imaging device (EPID) in eight patients treated with intensity modulated radiotherapy (IMRT), and to verify the accuracy of dose delivery to patients. The calculated dose map of the treatment planning system (TPS) was compared with the EPID based dose measured on the same plane with a gamma index method. The plan for each patient was verified prior to treatment with a diode array (MapCHECK) and portal dose image prediction (PDIP). To simulate possible patient positioning errors during treatment, outcomes were evaluated after an anthropomorphic phantom was displaced 5 and 10 mm in various directions. Based on 3%/3 mm criteria, the mean±SD passing rates of MapCHECK, PDIP (pre-treatment QA) for 47 IMRT were 99.8±0.1%, 99.0±0.7%, and, respectively. Besides, passing rates using transit dosimetry was 90.0±1.5% for the same condition. Setup errors of 5 and 10 mm reduced the mean passing rates by 1.3% and 3.0% (inferior to superior), 2.2% and 4.3% (superior to inferior), 5.9% and 10.9% (left to right), and 8.9% and 16.3% (right to left), respectively. These findings suggest that the transit dose-based IMRT verification method using EPID, in which the transit dose from patients is compared with the dose map calculated from the TPS, may be useful in verifying various errors including setup and/or patient positioning error, inhomogeneity and target motions.
关键词： Linear accelerator,Transit dose,Gamma index,EPID
更新于2025-09-04 15:30:14