Assessment of four dose calculation algorithms using IAEA-TECDOC-1583 with medium dependency correction factor (Kmed) application.

PURPOSE: This study discusses the measurement of dose in clinical commissioning tests described in IAEA-TECDOC-1583. It explores the application of Monte Carlo (MC) modelled medium dependency correction factors (Kmed) for accurate dose measurement in bone and lung materials using the CIRS phantom. METHODS: BEAMnrc codes simulate radiation sources and model radiation transport for 6 MV and 15 MV photon beams. CT images of the CIRS phantom are converted to an MC compatible phantom. The PTW 30013 farmer chamber measures doses within modeled CIRS phantom. Kmed are determined by averaging values from four central voxels within the sensitive volume of the farmer chamber. Kmed is calculated for Dm.m and Dw.w algorithm types in bone and lung media for both photon beams. RESULTS: Average modelled correction factors for Dm.m calculations using the farmer chamber are 0.976 (±0.1 %) for 6 MV and 0.979 (±0.1 %) for 15 MV in bone media. Correspondingly, correction factors for Dw.w calculations are 0.99 (±0.3 %) and 0.992 (±0.4 %), respectively. For lung media, average correction factors for Dm.m calculations are 1.02 (±0.3 %) for 6 MV and 1.022 (±0.4 %) for 15 MV. Correspondingly, correction factors for Dw.w calculations are 1.01 (±0.3 %) and 1.012 (±0.2 %), respectively. CONCLUSIONS: This study highlights the significant impact of applying Kmed on dose differences between measurement and calculation during the dose audit process.

Acesso a serviço de saúde e reabilitação auditiva de adultos e idosos durante o período inicial da pandemia COVID-19 no Brasil / Access to health service and hearing rehabilitation for adult and older adults during the initial period of the COVID-19 pandemic in Brazil / Acceso a servicios de salud yrehabilitación auditiva para adultos y ancianos durante el período inicial de la pandemia COVID-19 en Brasil

Introdução: A perda auditiva é uma deficiência comum na população mundial e contribui para dificuldade na comunicação verbal e redução da qualidade de vida, evidenciando a importância da identificação precoce, reabilitação e acompanhamento audiológico dessa deficiência para mitigar suas consequências. Durante a pandemia da COVID-19, as medidas restritivas diminuíram a capacidade de atendimento dos serviços de saúde auditiva e dificultaram a busca de auxílio para resolver problemas relacionados à adaptação aos dispositivos eletrônicos de amplificação sonora (DAES), sendo uma barreira no processo de reabilitação da perda auditiva. Objetivo: Caracterizar os usuários de DEAS e o processo inicial de reabilitação auditiva de adultos e idosos e verificar fatores associados ao retorno para a consulta de monitoramento auditivo durante o período inicial da pandemia da COVID-19.Métodos: Estudo observacional transversal com usuários adultos e idosos de um serviço ambulatorial de saúde auditiva com retorno para consulta de monitoramento auditivo agendada no período inicial da implementação das medidas restritivas da pandemia da COVID-19 no Brasil. Resultados: A maioria dos participantes conseguiu retornou para a consulta de monitoramento auditivo, sendo eles em sua maioria idosos, do sexo feminino e vacinados contra a COVID-19. Houve maior prevalência de adaptação adequada aos DAES. Não houve associação estatística entre as variáveis relacionadas à adaptação aos DAES, COVID-19 e saúde mental e o retorno à consulta de monitoramento auditivo. Conclusão: Os fatores relacionados à adaptação aos DAES, à COVID-19 ou à saúde mental não influenciaram o retorno à consulta de monitoramento auditivo na presente pesquisa. (AU)

Introduction: Hearing loss is a common disability in the world population and contributes to difficulty in verbal communication and reduced quality of life, highlighting the importance of early identification, rehabilitation and audiological monitoring of this disability to mitigate its consequences. During the COVID-19 pandemic, restrictive measures reduced the service capacity of hearing health services and made it difficult to seek help to solve problems related to adaptation to personal sound amplification products (PSAPs), being a barrier in the rehabilitation process of hearing loss. Aim: To characterize PSAPs users and the initial hearing rehabilitation process for adults and elderly people and verify the factors associated with the return to hearing monitoring consultations in the initial period of the COVID-19 pandemic. Methods: Cross-sectional observational study with adults and elderly people: elderly users of an outpatient hearing health service who return for a scheduled hearing monitoring consultation in the initial period of the implementation of restrictive measures of the COVID-19 pandemic in Brazil. Results: Most participants were able to return to the hearing monitoring clinic, the majority of whom were elderly, female and vaccinated against COVID-19. There was a higher prevalence of adequate adaptation to the PSAPs. There was no statistical association between variables related to adaptation to PSAPs, COVID-19 and mental health and return to hearing monitoring consultation. Conclusion: Factors related to adaptation to PSAPs, COVID-19 or mental health did not influence the return to hearing monitoring consultation in the present investigation. (AU)

Introducción: La pérdida auditiva es una discapacidad común en la población mundial y contribuye a la dificultad en la comunicación verbal y a la reducción de la calidad de vida, destacando la importancia de la identificación temprana, rehabilitación y seguimiento audiológico de esta discapacidad para mitigar sus consecuencias. Durante la pandemia de COVID-19, las medidas restrictivas redujeron la capacidad de atención de los servicios de salud auditiva y dificultaron la búsqueda de ayuda para resolver problemas relacionados con la adaptación a dispositivos electrónicos de amplificación del sonido (DEAS), siendo una barrera en el proceso de rehabilitación de la pérdida auditiva. Objetivo: Caracterizar a los usuarios de DEAS y el proceso inicial de rehabilitación auditiva de adultos y ancianos y verificar los factores asociados al retorno a las consultas de monitorización auditiva en el período inicial de la pandemia COVID-19. Métodos: Estudio observacional transversal con adultos y ancianos: ancianos usuarios de un servicio ambulatorio de salud auditiva que regresan para consulta de monitorización auditiva programada en el período inicial de la implementación de medidas restrictivas de la pandemia de COVID-19 en Brasil. Resultados: La mayoría de los participantes pudieron regresar a la clínica de monitorización auditiva, la mayoría de los cuales eran ancianos, mujeres y estaban vacunados contra COVID-19. Hubo mayor prevalencia de adaptación adecuada a la DEAS. No hubo asociación estadística entre variables relacionadas con adaptación a DEAS, COVID-19 y salud mental y retorno a consulta de monitorización auditiva. Conclusión: Los factores relacionados con la adaptación a DEAS, el COVID-19 o la salud mental no influyeron en el retorno a la consulta de monitorización auditiva en la presente investigación. (AU)

A deep-learning-based scatter correction with water equivalent path length map for digital radiography.

We proposed a new deep learning (DL) model for accurate scatter correction in digital radiography. The proposed network featured a pixel-wise water equivalent path length (WEPL) map of subjects with diverse sizes and 3D inner structures. The proposed U-Net model comprises two concatenated modules: one for generating a WEPL map and the other for predicting scatter using the WEPL map as auxiliary information. First, 3D CT images were used as numerical phantoms for training and validation, generating observed and scattered images by Monte Carlo simulation, and WEPL maps using Siddon's algorithm. Then, we optimised the model without overfitting. Next, we validated the proposed model's performance by comparing it with other DL models. The proposed model obtained scatter-corrected images with a peak signal-to-noise ratio of 44.24 ± 2.89 dB and a structural similarity index measure of 0.9987 ± 0.0004, which were higher than other DL models. Finally, scatter fractions (SFs) were compared with other DL models using an actual phantom to confirm practicality. Among DL models, the proposed model showed the smallest deviation from measured SF values. Furthermore, using an actual radiograph containing an acrylic object, the contrast-to-noise ratio (CNR) of the proposed model and the anti-scatter grid were compared. The CNR of the images corrected using the proposed model are 16% and 82% higher than those of the raw and grid-applied images, respectively. The advantage of the proposed method is that no actual radiography system is required for collecting training dataset, as the dataset is created from CT images using Monte Carlo simulation.

A Deep-Learning-Based Partial-Volume Correction Method for Quantitative 177Lu SPECT/CT Imaging.

With the development of new radiopharmaceutical therapies, quantitative SPECT/CT has progressively emerged as a crucial tool for dosimetry. One major obstacle of SPECT is its poor resolution, which results in blurring of the activity distribution. Especially for small objects, this so-called partial-volume effect limits the accuracy of activity quantification. Numerous methods for partial-volume correction (PVC) have been proposed, but most methods have the disadvantage of assuming a spatially invariant resolution of the imaging system, which does not hold for SPECT. Furthermore, most methods require a segmentation based on anatomic information. Methods: We introduce DL-PVC, a methodology for PVC of 177Lu SPECT/CT imaging using deep learning (DL). Training was based on a dataset of 10,000 random activity distributions placed in extended cardiac-torso body phantoms. Realistic SPECT acquisitions were created using the SIMIND Monte Carlo simulation program. SPECT reconstructions without and with resolution modeling were performed using the CASToR and STIR reconstruction software, respectively. The pairs of ground-truth activity distributions and simulated SPECT images were used for training various U-Nets. Quantitative analysis of the performance of these U-Nets was based on metrics such as the structural similarity index measure or normalized root-mean-square error, but also on volume activity accuracy, a new metric that describes the fraction of voxels in which the determined activity concentration deviates from the true activity concentration by less than a certain margin. On the basis of this analysis, the optimal parameters for normalization, input size, and network architecture were identified. Results: Our simulation-based analysis revealed that DL-PVC (0.95/7.8%/35.8% for structural similarity index measure/normalized root-mean-square error/volume activity accuracy) outperforms SPECT without PVC (0.89/10.4%/12.1%) and after iterative Yang PVC (0.94/8.6%/15.1%). Additionally, we validated DL-PVC on 177Lu SPECT/CT measurements of 3-dimensionally printed phantoms of different geometries. Although DL-PVC showed activity recovery similar to that of the iterative Yang method, no segmentation was required. In addition, DL-PVC was able to correct other image artifacts such as Gibbs ringing, making it clearly superior at the voxel level. Conclusion: In this work, we demonstrate the added value of DL-PVC for quantitative 177Lu SPECT/CT. Our analysis validates the functionality of DL-PVC and paves the way for future deployment on clinical image data.

Experimental comparison of cylindrical and plane parallel ionization chambers for reference dosimetry in continuous and pulsed scanned proton beams.

Objective. In this experimental work we compared the determination of absorbed dose to water using four ionization chambers (ICs), a PTW-34045 Advanced Markus, a PTW-34001 Roos, an IBA-PPC05 and a PTW-30012 Farmer, irradiated under the same conditions in one continuous- and in two pulsed-scanned proton beams.Approach. The ICs were positioned at 2 cm depth in a water phantom in four square-field single-energy scanned-proton beams with nominal energies between 80 and 220 MeV and in the middle of 10 × 10 × 10 cm3dose cubes centered at 10 cm or 12.5 cm depth in water. The water-equivalent thickness (WET) of the entrance window and the effective point of measurement was considered when positioning the plane parallel (PP) ICs and the cylindrical ICs, respectively. To reduce uncertainties, all ICs were calibrated at the same primary standards laboratory. We used the beam quality (kQ) correction factors for the ICs under investigation from IAEA TRS-398, the newly calculated Monte Carlo (MC) values and the anticipated IAEA TRS-398 updated recommendations.Main results. Dose differences among the four ICs ranged between 1.5% and 3.7% using both the TRS-398 and the newly recommendedkQvalues. The spread among the chambers is reduced with the newlykQvalues. The largest differences were observed between the rest of the ICs and the IBA-PPC05 IC, obtaining lower dose with the IBA-PPC05.Significance. We provide experimental data comparing different types of chambers in different proton beam qualities. The observed dose differences between the ICs appear to be related to inconsistencies in the determination of thekQvalues. For PP ICs, MC studies account for the physical thickness of the entrance window rather than the WET. The additional energy loss that the wall material invokes is not negligible for the IBA-PPC05 and might partially explain the lowkQvalues determined for this IC. To resolve this inconsistency and to benchmark MC values,kQvalues measured using calorimetry are needed.

Evaluation of radiation detectors for the determination of field output factors in Leksell Gamma Knife dosimetry using 3D printed phantom inserts.

The Leksell Gamma Knife® Perfexion™ and Icon™ have a unique geometry, containing 192 60Co sources with collimation for field sizes of 4 mm, 8 mm, and 16 mm. 4 mm and 8 mm collimated fields lack lateral charged particle equilibrium, so accurate field output factors are essential. This study performs field output factor measurements for the microDiamond, microSilicon, and RAZOR™ Nano detectors. 3D printed inserts for the spherical Solid Water® Phantom were fabricated for microDiamond detector, the microSilicon unshielded diode and the RAZOR™ Nano micro-ionisation chamber. Detectors were moved iteratively to identify the peak detector signal for each collimator, representing the effective point of measurement of the chamber. In addition, field output correction factors were calculated for each detector relative to vendor supplied Monte Carlo simulated field output factors and field output factors measured with a W2 scintillator. All field output factors where within 1.1 % for the 4 mm collimator and within 2.3 % for the 8 mm collimator. The 3D printed phantom inserts were suitable for routine measurements if the user identifies the effective point of measurement, and ensures a reproducible setup by marking the rotational alignment of the cylindrical print. Measurements with the microDiamond and microSilicon can be performed faster compared to the RAZOR™ Nano due to differences in the signal to noise ratio. All detectors are suitable for field output factor measurements for the Leksell Gamma Knife® Perfexion™ and Icon™.

Impact of scatter correction on personalized dosimetry in selective internal radiotherapy using 166Ho-PLLA: a single-center study including Monte-Carlo simulation, phantom and patient imaging.

BACKGROUND: Developments in transarterial radioembolization led to the conception of new microspheres loaded with holmium-166 (166Ho). However, due to the complexity of the scatter components in 166Ho single photon emission computed tomography (SPECT), questions about image quality and dosimetry are emerging. The aims of this work are to investigate the scatter components and correction methods to propose a suitable solution, and to evaluate the impact on image quality and dosimetry including Monte-Carlo (MC) simulations, phantom, and patient data. METHODS: Dual energy window (DEW) and triple energy window (TEW) methods were investigated for scatter correction purposes and compared using Contrast Recovery Coefficients (CRC) and Contrast to Noise Ratios (CNR). First, MC simulations were carried out to assess all the scatter components in the energy windows used, also to confirm the choice of the parameter needed for the DEW method. Then, MC simulations of acquisitions of a Jaszczak phantom were conducted with conditions mimicking an ideal scatter correction. These simulated projections can be reconstructed and compared with real acquisitions corrected by both methods and then reconstructed. Finally, both methods were applied on patient data and their impact on personalized dosimetry was evaluated. RESULTS: MC simulations confirmed the use of k = 1 for the DEW method. These simulations also confirmed the complexity of scatter components in the main energy window used with a high energy gamma rays component of about half of the total counts detected, together with a negligible X rays component and a negligible presence of fluorescence. CRC and CNR analyses, realized on simulated scatter-free projections of the phantom and on scatter corrected acquisitions of the same phantom, suggested an increased efficiency of the TEW method, even at the price of higher level of noise. Finally, these methods, applied on patient data, showed significant differences in terms of non-tumoral liver absorbed dose, non-tumoral liver fraction under 50 Gy, tumor absorbed dose, and tumor fraction above 150 Gy. CONCLUSIONS: This study demonstrated the impact of scatter correction on personalized dosimetry on patient data. The use of a TEW method is proposed for scatter correction in 166Ho SPECT imaging.

Assessment of refractive outcomes in eyes that underwent intraocular lens implantation in the posterior chamber but not "in-the-capsular bag:" A comparative retrospective study.

PURPOSE: The purpose of this study was to report visual and refractive outcomes in eyes that underwent intraocular lens (IOL) fixation in the absence of capsular support. METHODS: This was a retrospective chart review of cases undergoing posterior chamber iris-fixated IOL (IFIOL) and scleral-fixated IOL (SFIOL) implants from June 2014 to March 2020 with more than 3 months of follow-up and having a preoperative best-corrected visual acuity of 20/80 and more. RESULTS: Records of 120 eyes of 112 patients were reviewed. The mean age of the patients was 46.9 ± 22.3 (14.4-98.0) years, and 62% (n = 70) of participants were male. Most of the eyes (102: 85%) were aphakic at the time of surgery. The mean follow-up was 22.95 ± 17.1 months. The efficacy index of sutured IFIOL and glued SFIOL outperformed sutured SFIOL at 3 months and final visits postoperatively (P < 0.001). All techniques studied here resulted in a similar safety index at 3 months (P = 0.4). The mean predictive error (postoperative spherical equivalent refraction minus intended target refraction) was +0.07 ± 1.5 D and -0.12 ± 1.4 D at 3 months and the final postoperative visit, respectively. CONCLUSION: The studied techniques have relatively good visual and refractive outcomes in this series. In addition, techniques involving a small corneal incision with foldable IOL fixation to the iris or scleral tissue have superior efficacy and safety indices compared to creating large corneoscleral wounds for rigid IOL fixation techniques.

Improvement of diffusion tensor imaging-based tractography by free-water correction in nonedematous gliomas: assessment with brain mapping.

OBJECTIVE: The free-water correction algorithm (Freewater Estimator Using Interpolated Initialization [FERNET]) can be applied to standard diffusion tensor imaging (DTI) tractography to improve visualization of subcortical bundles in the peritumoral area of highly edematous brain tumors. Interest in its use for presurgical planning in purely infiltrative gliomas without peritumoral edema has never been evaluated. Using subcortical maps obtained with direct electrostimulation (DES) in awake surgery as a reference standard, the authors sought to 1) assess the accuracy of preoperative DTI-based tractography with FERNET in a series of nonedematous glioma patients, and 2) determine its potential usefulness in presurgical planning. METHODS: Based on DES-induced functional disturbances and tumor topography, the authors retrospectively reconstructed the putatively stimulated bundles and the peritumoral tracts of interest (various associative and projection pathways) of 12 patients. The tractography data obtained with and without FERNET were compared. RESULTS: The authors identified 21 putative tracts from 24 stimulation sites and reconstituted 49 tracts of interest. The number of streamlines of the putative tracts crossing the DES area was 26.8% higher (96.04 vs 75.75, p = 0.016) and their volume 20.4% higher (13.99 cm3 vs 11.62 cm3, p < 0.0001) with FERNET than with standard DTI. Additionally, the volume of the tracts of interest was 22.1% higher (9.69 cm3 vs 7.93 cm3, p < 0.0001). CONCLUSIONS: Free-water correction significantly increased the anatomical plausibility of the stimulated fascicles and the volume of tracts of interest in the peritumoral area of purely infiltrative nonedematous gliomas. Because of the functional importance of the peritumoral zone, applying FERNET to DTI could have potential implications on surgical planning and the safety of glioma resection.

Bias correction models for electronic health records data in the presence of non-random sampling.

Electronic health records (EHRs) contain rich clinical information for millions of patients and are increasingly used for public health research. However, non-random inclusion of subjects in EHRs can result in selection bias, with factors such as demographics, socioeconomic status, healthcare referral patterns, and underlying health status playing a role. While this issue has been well documented, little work has been done to develop or apply bias-correction methods, often due to the fact that most of these factors are unavailable in EHRs. To address this gap, we propose a series of Heckman type bias correction methods by incorporating social determinants of health selection covariates to model the EHR non-random sampling probability. Through simulations under various settings, we demonstrate the effectiveness of our proposed method in correcting biases in both the association coefficient and the outcome mean. Our method augments the utility of EHRs for public health inferences, as we show by estimating the prevalence of cardiovascular disease and its correlation with risk factors in the New York City network of EHRs.

Assessment of attenuation properties for SLA and SLS 3D-printing materials in X-ray imaging and nuclear medicine.

In recent years, access to 3D printers has become increasingly affordable. Alongside industrial and private applications, the significance of 3D printing in the clinical context is also growing. For instance, 3D printing processes enable the production of individual anatomical models that can be used to support patient communication or aid in surgical planning. While filament 3D printing is common, stereolithography (SLA) and selective laser sintering (SLS) printing processes offer higher precision. For the use of 3D printing materials in radiology, understanding their attenuation properties concerning ionizing radiation is crucial. Polymethyl methacrylate (PMMA) serves as an important reference material for radiological applications in this regard. In this research, linear- and mass attenuation coefficients of 38 SLA-/SLS-materials from Formlabs (Somerville, Massachusetts, USA) and PMMA will be determined through intensity measurements in nuclear medicine for the radionuclides technetium-99 m and iodine-131, as well as for X-ray imaging in the range of 60 kVp - 110 kVp tube voltage. Based on the mass attenuation coefficients, correction factors in respect to PMMA will be calculated for each material. A significant number of materials exhibit a deviance within approximately ±5% in respect to PMMA regardless of radiation energy. However, certain materials from the dental and industrial application show deviances up to +500% at the lower end of radiation energy spectrum. In conclusion, most materials can be considered equivalent to PMMA with only minor adjustments required. Materials with high deviances can be utilized as high-contrast materials in custom X-ray phantoms.

Quantitative assessment of muscle activity of back and lower extremities, whole body sagittal alignment, body sway, and health-related quality of life in adult spinal deformity patients before and after spinopelvic correction surgery: From the standpoint of the "cone of economy".

BACKGROUND AND AIMS: Pain and muscle fatigue in the low back and lower extremity associated with adult spinal deformity (ASD) markedly limit daily activities and affect quality of life. This study aimed to clarify if spinal correction surgery decreases the muscle activity requirements in relation to alignment and balance parameters. METHODS: Integrated electromyogram (I-EMG) studies of the low back and lower extremity in addition to whole body alignment, body sway, and health-related quality of life (HRQOL) were evaluated in 16 patients with ASD before and after surgery. Sixteen healthy volunteers were included as control subjects. Muscle activities of the bilateral lumbar paravertebral, biceps femoris, rectus femoris, gastrocnemius, and tibialis anterior were measured using surface electromyogram in both resting and working standing positions. Surgical outcomes were based on improvements in muscle fatigue using the sum of the whole muscle I-EMGs and body sway. HRQOL was evaluated by SRS-22r, which measures 4 domains (function, pain, self-image, mental health) and subtotal scores. RESULTS: In controls, the sum of the 10 whole I-EMGs (mVms; mean ± SD) was 3316 ± 1247 in the resting standing position and 5625 ± 2065 in the working standing position. The I-EMG values were higher in ASD patients than in healthy subjects; in the resting standing position, the sum of the whole 10 I-EMGs significantly decreased from baseline (9125 ± 3529) to 3 (6088 ± 1793) and 6 (6381 ± 1776) months postoperatively (p < 0.01). In the working standing position, the sum in ASD patients also significantly decreased from baseline (14,160 ± 5474) to 3 (8085 ± 2540) and 6 (8557 ± 3025) months postoperatively (p < 0.01). I-EMG values did not differ significantly between the 3- and 6-month time points in either condition. Body sway was also improved postoperatively at 3 months and maintained at 6 months along with the amelioration of whole-body sagittal alignment, and 4 domains and subtotal SRS-22r scores significantly increased postoperatively. CONCLUSION: Following spinopelvic correction surgery, whole body sagittal alignment was improved, and muscle activity based on I-EMG and body sway were significantly decreased. The SRS-22r scores after surgery also indicated significant improvement, suggesting that muscle fatigue in the standing position was ameliorated, i.e., the "cone of economy" was normalized.

RPCA-based techniques for pattern extraction, hotspot identification and signal correction using data from a dense network of low-cost NO2 sensors in London.

High-density low-cost air quality sensor networks are a promising technology to monitor air quality at high temporal and spatial resolution. However the collected data is high-dimensional and it is not always clear how to best leverage this information, particularly given the lower data quality coming from the sensors. Here we report on the use of robust Principal Component Analysis (RPCA) using nitrogen dioxide data obtained from a recently deployed dense network of 225 air pollution monitoring nodes based on low-cost sensors in the Borough of Camden in London. RPCA addresses the brittleness of singular value decomposition towards outliers by using a decomposition of the data into low-rank and sparse contributions, with the latter containing outliers. The modal decomposition enabled by RPCA identifies major periodic patterns including spatial and temporal bias, dominant spatial variance, and north-south bias. The five most descriptive components capture 98 % of the data's variance, achieving a compression by a factor of 1500. We present a new technique that uses the sparse part of the data to identify hotspots. The data indicates that at the locations of the top 15 % most susceptible nodes in the network, the model identifies 23 % more hotspots than in all other locations combined. Moreover, the median hotspot event at these at-risk locations exceeds the mean NO2concentration by 33µg/m3. We show the potential of RPCA for signal correction; it corrects random errors yielding a reference signal with R2>0.8. Moreover, RPCA successfully reconstructs missing data from a sensor with R2=0.72 from the rest of the sensor network, an improvement upon PCA of around 50 %, allowing air quality estimations even if a sensor is out of use temporarily.

Fano cavity test and investigation of the response of the Roos chamber irradiated by proton beams in perpendicular magnetic fields up to 1 T.

Objective. The aim of this work is to investigate the response of the Roos chamber (type 34001) irradiated by clinical proton beams in magnetic fields.Approach. At first, a Fano test was implemented in Monte Carlo software package GATE version 9.2 (based on Geant4 version 11.0.2) using a cylindrical slab geometry in a magnetic field up to 1 T. In accordance to an experimental setup (Fuchset al2021), the magnetic field correction factorskQB⃗of the Roos chamber were determined at different energies up to 252 MeV and magnetic field strengths up to 1 T, by separately simulating the ratios of chamber signalsMQ/MQB⃗,without and with magnetic field, and the dose-conversion factorsDw,QB⃗/Dw,Qin a small cylinder of water, with and without magnetic field. Additionally, detailed simulations were carried out to understand the observed magnetic field dependence.Main results. The Fano test was passed with deviations smaller than 0.25% between 0 and 1 T. The ratios of the chamber signals show both energy and magnetic field dependence. The maximum deviation of the dose-conversion factors from unity of 0.22% was observed at the lowest investigated proton energy of 97.4 MeV andB⃗= 1 T. The resultingkQB⃗factors increase initially with the applied magnetic field and decrease again after reaching a maximum at around 0.5 T; except for the lowest 97.4 MeV beam that show no observable magnetic field dependence. The deviation from unity of the factors is also larger for higher proton energies, where the maximum lies at 1.0035(5), 1.0054(7) and 1.0069(7) for initial energies ofE0= 152, 223.4 and 252 MeV, respectively.Significance. Detailed Monte Carlo studies showed that the observed effect can be mainly attributed to the differences in the transport of electrons produced both outside and inside of the air cavity in the presence of a magnetic field.

Calibration system correction factor for measuring the reference air kerma rate (RAKR) applied to high dose rate192Ir sources (HDR).

The aim of this study was to use computer simulation to analyze the impact of the aluminum fixing support on the Reference Air Kerma (RAK), a physical quantity obtained in a calibration system that was experimentally developed in the Laboratory of Radiological Sciences of the University of the State of Rio de Janeiro (LCR-UERJ). Correction factors due to scattered radiation and the geometry of the192Ir sources were also sought to be determined. The computational simulation was validated by comparing some parameters of the experimental results with the computational results. These parameters were: verification of the inverse square law of distance, determination of (RAKR), analysis of the source spectrum with and without encapsulation, and the sensitivity curve of the Sourcecheck 4PI ionization chamber response, as a function of the distance from the source along the axial axis, using the microSelectron-v2 (mSv2) and GammaMedplus (GMp) sources. Kerma was determined by activity in the Reference air, with calculated values of 1.725 × 10-3U. Bq-1and 1.710 × 10-3U. Bq-1for the ionization chamber NE 2571 and TN 30001, respectively. The expanded uncertainty for these values was 0.932% and 0.919%, respectively, for a coverage factor (k = 2). The correction factor due to the influence of the aluminum fixing support for measurements at 1 cm and 10 cm from the source was 0.978 and 0.969, respectively. The geometric correction factor of the sources was ksg= 1.005 with an expanded uncertainty of 0.7% for a coverage factor (k = 2). This value has a difference of approximately 0.2% compared to the experimental values.

A practical method of estimating medium-heterogeneity corrected dose without a Monte Carlo calculation in ocular brachytherapy using 125I COMS plaques.

PURPOSE: To provide a practical method of estimating medium-heterogeneity corrected dose without a Monte Carlo (MC) calculation in ocular brachytherapy using 125I Collaborative Ocular Melanoma Study (COMS) plaques. METHODS AND MATERIALS: Using egs_brachy, MC simulations (1) under task group-43 assumptions with fully loaded seed configurations in water (HOMO) and (2) with effects of plaque backing, insert and inter-seed interactions (HETERO) were performed for seven 125I COMS plaques (10 mm-22 mm in diameter), and homogeneous dose (DHOMO) and heterogeneous dose (DHETERO) for central-axis and off-axis points were determined. For DHOMO, 85 Gy was normalized to a depth of 5 mm. Central-axis heterogeneity correction factors (HCFs) from a depth of 0 mm (inner sclera) to 22 mm (opposite retina) were derived from a ratio of DHETERO to DHOMO. Off-axis HCFs for optic disc/macula and lens as a function of distance from optic disc/macula (DT/MT) for various basal dimensions of tumor (BD/BM) were derived from DHETERO/DHOMO. RESULTS: Central-axis HCF varied with a dose reduction of 10.3-19.8% by heterogeneity. Off-axis HCF for optic disc/macula varied significantly depending on DT/MT and BD/BM with a dose reduction of 11.3-38.3%. Off-axis HCF for lens had a dependence on MT and BM with its variation of 11.0-19.0%. A clinical example of using HCFs to estimate DHETERO was presented. CONCLUSIONS: The practical method of using depth-dependent central-axis HCF and DT/MT- and BD/BM-dependent off-axis HCF provided in this study will facilitate a heterogeneous dose estimate for 125I COMS plaques without MC calculations.

Correcting for Sampling Error in between-Cluster Effects: An Empirical Bayes Cluster-Mean Approach with Finite Population Corrections.

With clustered data, such as where students are nested within schools or employees are nested within organizations, it is often of interest to estimate and compare associations among variables separately for each level. While researchers routinely estimate between-cluster effects using the sample cluster means of a predictor, previous research has shown that such practice leads to biased estimates of coefficients at the between level, and recent research has recommended the use of latent cluster means with the multilevel structural equation modeling framework. However, the latent cluster mean approach may not always be the best choice as it (a) relies on the assumption that the population cluster sizes are close to infinite, (b) requires a relatively large number of clusters, and (c) is currently only implemented in specialized software such as Mplus. In this paper, we show how using empirical Bayes estimates of the cluster means can also lead to consistent estimates of between-level coefficients, and illustrate how the empirical Bayes estimate can incorporate finite population corrections when information on population cluster sizes is available. Through a series of Monte Carlo simulation studies, we show that the empirical Bayes cluster-mean approach performs similarly to the latent cluster mean approach for estimating the between-cluster coefficients in most conditions when the infinite-population assumption holds, and applying the finite population correction provides reasonable point and interval estimates when the population is finite. The performance of EBM can be further improved with restricted maximum likelihood estimation and likelihood-based confidence intervals. We also provide an R function that implements the empirical Bayes cluster-mean approach, and illustrate it using data from the classic High School and Beyond Study.

Motion-compensated image reconstruction for improved kidney function assessment using dynamic contrast-enhanced MRI.

Accurately measuring renal function is crucial for pediatric patients with kidney conditions. Traditional methods have limitations, but dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) provides a safe and efficient approach for detailed anatomical evaluation and renal function assessment. However, motion artifacts during DCE-MRI can degrade image quality and introduce misalignments, leading to unreliable results. This study introduces a motion-compensated reconstruction technique for DCE-MRI data acquired using golden-angle radial sampling. Our proposed method achieves three key objectives: (1) identifying and removing corrupted data (outliers) using a Gaussian process model fitting with a k -space center navigator, (2) efficiently clustering the data into motion phases and performing interphase registration, and (3) utilizing a novel formulation of motion-compensated radial reconstruction. We applied the proposed motion correction (MoCo) method to DCE-MRI data affected by varying degrees of motion, including both respiratory and bulk motion. We compared the outcomes with those obtained from the conventional radial reconstruction. Our evaluation encompassed assessing the quality of images, concentration curves, and tracer kinetic model fitting, and estimating renal function. The proposed MoCo reconstruction improved the temporal signal-to-noise ratio for all subjects, with a 21.8% increase on average, while total variation values of the aorta, right, and left kidney concentration were improved for each subject, with 32.5%, 41.3%, and 42.9% increases on average, respectively. Furthermore, evaluation of tracer kinetic model fitting indicated that the median standard deviation of the estimated filtration rate ( σ F T ), mean normalized root-mean-squared error (nRMSE), and chi-square goodness-of-fit of tracer kinetic model fit were decreased from 0.10 to 0.04, 0.27 to 0.24, and, 0.43 to 0.27, respectively. The proposed MoCo technique enabled more reliable renal function assessment and improved image quality for detailed anatomical evaluation in the case of bulk and respiratory motion during the acquisition of DCE-MRI.

Do expenditures on public health reduce preventable mortality in the long run? Evidence from the Canadian provinces.

BACKGROUND: Investments in public health - prevention of illnesses, and promotion, surveillance, and protection of population health - may improve population health, however, effects may only be observed over a long period of time. OBJECTIVE: To investigate the potential long-run relationship between expenditures on public health and avoidable mortality from preventable causes. METHODS: We focused on the country spending the most on public health in the OECD, Canada. We constructed a longitudinal dataset on mortality, health care expenditures and socio-demographic information covering years 1979-2017 for the ten Canadian provinces. We estimated error correction models for panel data to disentangle short-from long-run relationships between expenditures on public health and avoidable mortality from preventable causes. We further explored some specific causes of mortality to understand potential drivers. For comparison, we also estimated the short-run relationship between curative expenditures and avoidable mortality from treatable causes. RESULTS: We find evidence of a long-run relationship between expenditures on public health and preventable mortality, and no consistent short-run associations between these two variables. Findings suggest that a 1% increase in expenditures on public health could lead to 0.22% decrease in preventable mortality. Reductions in preventable mortality are greater for males (-0.29%) compared to females (-0.09%). These results are robust to different specifications. Reductions in some cancer and cardiovascular deaths are among the probable drivers of this overall decrease. By contrast, we do not find evidence of a consistent short-run relationship between curative expenditures and treatable mortality, except for males. CONCLUSION: This study supports the argument that expenditures on public health reap health benefits primarily in the long run, which, in this case, represents a reduction in avoidable mortality from preventable causes. Reducing public health expenditures on the premise that they have no immediate measurable benefits might thus harm population health outcomes in the long run.

Beam quality correction factors for ionization chambers in a 0.35 T magnetic resonance (MR)-linac - A Monte Carlo study.

PURPOSE: The purpose of this study was to directly calculate [Formula: see text] correction factors for four cylindrical ICs for a 0.35 T MR-linac using the Monte Carlo (MC) method. METHODS: A previously-validated TOPAS/GEANT4 MC head model of the 0.35 T MR-linac was employed. The MR-compatible Exradin A12, A1SL, A26, and A28 cylindrical ICs were modeled considering the dead volume in the air cavity. The [Formula: see text] correction factor was determined for initial electron energies of 5-7 MeV. The correction factor was calculated for all four angular orientations in the lateral plane. The impact of the 0.35 T magnetic field on the IC response was also investigated. RESULTS: The maximum beam quality dependence in the [Formula: see text] exhibited by the A12, A1SL, A26, and A28 ICs was 1.10 %, 2.17 %, 0.81 %, and 1.75 %, respectively, considering all angular orientations. The magnetic field dependence was < 1 % and the maximum [Formula: see text] correction was < 2 % when the detector was aligned along the direction of the magnetic field at 0° and 180° angles. The A12 IC over-responded up to 5.40 % for the orthogonal orientation. An asymmetry in the response of up to 8.30 % was noted for the A28 IC aligned at 90° and 270° angles. CONCLUSIONS: A parallel orientation for the IC, with respect to the magnetic field, is recommended for reference dosimetry in MRgRT. Both over and under-response in the IC signal was noted for the orthogonal orientations, which is highly dependent on the cavity diameter, cavity length, and the dead volume.