Dose Rate Research Articles

Natural Radionuclides Concentrations and Associated Radiation Hazard of Some Building Rocks Used in Taiz City, Yemen

Building materials comprise a diverse range of natural rocks that contain varying mineral components including radionuclides. Gamma spectrometry-based high-purity Germanium detectors were utilized to measure the activity concentrations of natural radionuclides: Radium-226 (226Ra), Thorium-232 (232Th), and Potassium-40 (40K) in various building rock samples found within and surrounding Taiz city. The activity concentrations of 226Ra, 232Th, and 40K vary from 27.79 ± 0.77 to 234.49 ± 3.13 Bq.kg-1, 25.82 ± 0.40 to 415.31 ± 2.47 Bq.kg-1, and 457.91±2.61 to 1139.56 ± 5.43 Bq.kg-1 with overall average value of 71.55 Bq.kg-1, 93.87 Bq.kg-1, 966.88 Bq.kg-1 respectively, these values were higher than the permissible thresholds. Furthermore, several radiation hazard indices were estimated including the radium equivalent (Raeq), the external hazard index (Hex), the internal hazard index (Hin), the gamma level index (Iɤ), the dose rate(Dɤ), the annual effective dose equivalent (AEDE), the excess lifetime cancer risk (ELCR), and the annual gonadal dose equivalent (AGDE). The findings illustrated that Basalt rocks have the minimum values of radiation hazard indices while the Himatite rocks have the maximum values of radiation hazard. The average values of radiation risks for most of building rocks fall below the recommended limits for safety. Based on the Radiation hazard indices of building rock samples, it can be concluded that with the exception of hematite rocks, all the examined rocks are considered safe for use in construction materials and pose non-significant radiation risks. The awareness about natural radioactivity levels of building rocks is critical for planning and performing strategies in radiation safety of buildings.

Mobile vs Fixed Fluoroscopy System for EVAR Image Quality and Radiation Doses for Patients and Professionnals: Mobile C-Arm vs Hybrid Room for EVAR

Abstract Background Allowing less invasive treatments, endovascular aortic repair (EVAR) has become the gold standard worldwide for the treatment of abdominal aortic aneurysms, leading to questions regarding staff and patients’ exposure to radiation. Widely performed in our center, EVAR was initially carried out on mobile C-arm (Cios-alpha, Siemens). Since 2022, EVAR was then performed in a hybrid room (Artis-Pheno, Siemens). Aims The aim of this study is to compare image quality and patients and professionals’ radiation exposure between both systems. Methods Image quality has been tested for fluoroscopy and fluorography mode on the moving system, with PMMA plates and copper disc. A Radcal ionization chamber was used to measure patient skin dose. Dosimetric and clinical parameters (e.i. Kerma, fluoroscopy time, BMI…) were recorded for 79 and 43 patients, respectively, on mobile C-arm and hybrid room. Staff exposure was measured with thermoluminescent detectors, on an anthropomorphic phantom, representative of the physician. Scattered radiation was created by irradiating PMMA plates. Different radiation protection gears have been tested comparable to daily clinical use. Results We showed that using the fluoroscopy mode, Cios-alpha was more irradiating for similar image quality as compared to the Artis-Pheno. Moreover, using the fluorography mode, Artis-Pheno provided a comparable dose rate but significantly better image quality. When comparing similar patient cohorts (BMI, sex), kerma was twice higher on Artis-Pheno due to fluorography, accounting for 27% of the total dose. In terms of staff exposure, the dose rate decreased by 51% and 99% in fluoroscopy, and 22% and 99% in fluorography when using Artis-Pheno compared to Cios-alpha (respectively, without any and with radiation protection gear). Conclusion Our study highlights the advantage of a fixed system (hybrid room) in term of both image quality and staff exposure compared to mobile system. However, particular attention must be paid to optimize protocols of such a machine to guarantee the best possible radiation protection for the patient.

Combined optimization of spot positions and weights for better FLASH proton therapy.

In Intensity Modulated Proton Therapy (IMPT), the weights of individual pencil-beams or spots are optimized to fulfil dosimetric constraints. Theses spots are usually located on a regular lattice and their positions are fixed during optimization. In many cases, the range of spot weights may however be limited, leading sometimes to sub-optimal plan quality. An emblematic use case is the delivery of a plan at ultra-high dose rate (FLASH-RT), for which the spot weights are typically constrained to high values. To improve further the quality of IMPT FLASH plans, we propose here a novel algorithm to optimize both the spot weights and positions directly based on the objectives defined by the treatment planner. For all cases considered, optimizing the spot positions lead to an enhanced dosimetric score, while maintaining a high dose rate. Overall, this approach resulted in a substantial plan quality improvement compared to optimizing only the spot weights, and in a similar execution time.

Statistical evaluation of individual external exposure dose of outdoor worker and ambient dose rate at evacuation ordered zones after the Fukushima Daiichi nuclear power station accident.

Following the accident at the Fukushima Daiichi Nuclear Power Station, evacuation orders were issued for the surrounding communities. In order to lift the evacuation order, it is necessary to determine individual external doses in the evacuated areas. The purpose of this study was to determine the quantitative relationship between individual external doses and ambient dose rates per hour as conversion coefficients.
More specifically, individual external doses of Tokyo Electric Power Company Holdings employees in difficult-to-return zone were measured broadly over a long period (FY2020 to FY2022). To obtain highly accurate estimates, we used not only ambient dose rates based on airborne radiological monitoring data, but also Integrated dose rate map data that had been statistically corrected to correspond to local ambient dose rate gradients on the ground.
 As a result, the conversion coefficients based on the ambient dose rate map measured by airborne radiological monitoring were 0.42 for the Evacuation-Order Lifted Zones (ELZs), 0.37 for the Special Zones for Reconstruction and Rehabilitation (SZRRs), and 0.47 for the Difficult-to-Return Zones without a SZRRs (DRZs). On the other hand, the conversion coefficients based on the Integrated dose rate map which is a highly accurate dose rate map based on statistical analysis of various types of monitoring that have been studied in government projects in recent years, were 0.78 for the ELZs, 0.72 for the SZRRs and 0.82 for the DRZs. Using these conversion coefficients, the individual external dose can be estimated from two representative ambient dose rate maps provided by the government.&#xD.

Absorbed dose rates and biological consequences of discrete alpha-emitting particles embedded in tissue

This study calculates dose rate in Gy y-1 for individual dust, soil, and sediment particles that contain significant amounts of alpha-emitting uranium or thorium. When inhaled or ingested, these particles deliver radiation dose to organs where they embed. The presented method uses X-ray microscopy to measure alpha emitting elements in environmental microparticles, followed by calculation of dose rates delivered to the targeted volume of tissues that surround embedded microparticles. The example calculations use a real-world, 89% uranium house dust particle.

Practical experience with initial quality assurance of a high dose rate brachytherapy grid-based Boltzmann solver algorithm.

The purpose of this study was to validate the use of a model-based dose calculation algorithm (MBDCA), Acuros BV, for high dose rate brachytherapy treatment planning for a community-based hospital with a Bravos afterloader. Based on published AAPM recommendations, this work details a practical approach for community-based clinics to complete initial validation of Acuros BV, in order to add a MBDCA to a TG-43 based brachytherapy treatment planning program. Source dimensions and materials used in Acuros BV and TG-43 source models were compared to the physical source. TG-186 testing was completed with standardized test cases externally calculated with Monte Carlo compared to locally calculated with Acuros BV. Point doses calculated using TG-43 were compared to those calculated with Acuros BV in water at various dose grid settings. Secondary dose check software was used to evaluate dose distributions resembling clinical patient plans, both in water and on CT datasets representative of patient anatomy. The major source of discrepancy of source models was the length of modeled steel cable. TG-186 testing showed that the largest differences between Monte Carlo and Acuros BV dose distributions were located along the source axis for cases calculated in water, as well as located in regions of high dose gradients and within the applicator for the case calculated with a generic shielded applicator. An audit of point doses calculated with both TG-43 and Acuros BV in water found that dose grid settings significantly affected agreement. Secondary dose check software indicated that Acuros BV functioned satisfactorily, and a 5% threshold was adopted for secondary dose checks on gynecologic plans. This validation process indicated that Acuros BV met expected standards and affirmed its suitability for integration into this clinical practice's brachytherapy treatment planning.

Optimization of treatment workflow for 0.35T MR-Linac system.

This study presents a novel and comprehensive framework for evaluating magnetic resonance guided radiotherapy (MRgRT) workflow by integrating the Failure Modes and Effects Analysis (FMEA) approach with Time-Driven Activity-Based Costing (TDABC). We assess the workflow for safety, quality, and economic implications, providing a holistic understanding of the MRgRT implementation. The aim is to offer valuable insights to healthcare practitioners and administrators, facilitating informed decision-making regarding the 0.35T MRIdian MR-Linac system's clinical workflow. For FMEA, a multidisciplinary team followed the TG-100 methodology to assess the MRgRT workflow's potential failure modes. Following the mitigation of primary failure modes and workflow optimization, a treatment process was established for TDABC analysis. The TDABC was applied to both MRgRT and computed tomography guided RT (CTgRT) for typical five-fraction stereotactic body RT (SBRT) treatments, assessing total workflow and costs associated between the two treatment workflows. A total of 279 failure modes were identified, with 31 categorized as high-risk, 55 as medium-risk, and the rest as low-risk. The top 20% risk priority numbers (RPN) were determined for each radiation oncology care team member. Total MRgRT and CTgRT costs were assessed. Implementing technological advancements, such as real-time multi leaf collimator (MLC) tracking with volumetric modulated arc therapy (VMAT), auto-segmentation, and increasing the Linac dose rate, led to significant cost savings for MRgRT. In this study, we integrated FMEA with TDABC to comprehensively evaluate the workflow and the associated costs of MRgRT compared to conventional CTgRT for five-fraction SBRT treatments. FMEA analysis identified critical failure modes, offering insights to enhance patient safety. TDABC analysis revealed that while MRgRT provides unique advantages, it may involve higher costs. Our findings underscore the importance of exploring cost-effective strategies and key technological advancements to ensure the widespread adoption and financial sustainability of MRgRT in clinical practice.

Tissue Dose-rate Kernels for Bremsstrahlung Exposure from Internal Electron Emitters.

Radionuclides emitting high-energy beta rays are frequently employed for therapeutic purposes in the field of medicine. However, it is widely recognized that such radionuclides have the potential to generate in vivo bremsstrahlung radiation. This research study focused on investigating the dose rate of bremsstrahlung radiation emanating from a radioactive source embedded in a patient. To accomplish this, we estimate the spectral energy distribution of the generated bremsstrahlung. By employing this spectral distribution, we present a novel method for estimating the bremsstrahlung dose rate kernel applicable to a given combination of source and material. This method considers photon buildup and attenuation, as well as the encapsulation of the radiation source. Furthermore, we provide formulas for both monoenergetic electrons and beta-transition electrons that account for radioactive decay.

Assessment of radiation exposure in the phosphate mining area of Gafsa (Southeastern Tunisia)

ABSTRACT This study investigates the radiological health implications of sixty-three (63) samples of soil, food, and drinking water collected from the phosphate mining area of Gafsa in Southeastern Tunisia. Additionally, it assesses the exposure to radon concentrations in houses located around the phosphate mining sites. The activity concentrations in soil samples were found to be 382.1, 36.1 and 16.3 Bq kg−1 respectively for 40K, 232Th and 226Ra. The average activity of 232Th was higher than worldwide average value of 30 Bq kg−1. Eleven (11) radiological hazard parameters were computed based on various exposure scenarios including external gamma dose rate (GDR), annual effective dose (AED) and risk assessment (RA). The calculated GDR values were of 3.2 nGy h−1 in food and 45.4 nGy h−1 in soil samples, while the average AED values were of 3.9 µSv y−1 in food and 83.5 µSv y−1 in soil samples. Internal AED due to ingestion of radionuclides was found to have a mean value of 0.1 µSv y−1 in soil, 264.4 µSv y−1 in food and 10 µSv y−1 in drinking water samples. The AED values due to inhalation of soil-dust and radon were assessed to be 2.1 and 1.2 µSv y−1, respectively. The RA average values in food and drinking water samples were found to be 3 × 10−5 and 2.4 × 10−4, respectively. Based on the exposure pathway, inhalation of radioactivity through soil and radon resulted in highest total AED values, which remained below the reference limit. This was followed by internal exposure, with total AED values of 274.5 µSv y−1.

Maximum tumor diameter and renal function can predict the declining surface dose rate after 177Lu-Dotatate: preliminary results of single institution in Japan.

This study aimed to develop a user-friendly prediction formula for dose rate adjustment after initial 177Lu-Dotatate therapy from a prospective observational study of patients. This study included consenting patients in a prospective observational study who underwent their firsttreatment in four cycles of 177Lu-Dotatate treatment at our hospital between January 2022 and February 2024. All patients received 7.4GBq of 177Lu-Dotatate. The prediction formula was derived from the regression analysis of tumor-related factors and renal function. Creatinine clearance was estimated using the Cockcroft-Gault equation in this study for renal function. Among the 13 patients (seven males, six females, median age: 59years), logarithmically transformed total tumor volume (cc) and maximum tumor diameter (mm) of primary tumors or metastases showed strong correlations (p < 0.001, R2 = 0.897). As such, the maximum tumor diameter was used as the tumor parameter in the prediction formula. Additionally, maximum tumor diameter and creatinine clearance showed strong (p < 0.001, R2 = 0.768) and moderate (p = 0.013, R2 = 445) correlations, respectively, with the ratio of the dose rate 5.5-h post-administration to the dose rate immediately post-administration (%) at 1m from the body surface. The resulting formula, 51.4 + 0.360 × maximum tumor diameter (mm) - 0.212 × creatinine clearance (ml/min), demonstrated an extremely strong correlation (p < 0.001, R2 = 0.937). The present study showed that the maximum tumor diameter and renal function affected the declining the dose rate of patients surface after 177Lu-Dotatate, which can inform post-administration dose rate management and potentially facilitate outpatient treatment in Japan.

Pulsed Reduced Dose Rate Re-Irradiation for Patients with Recurrent Grade 2 Gliomas

Abstract BACKGROUND Patients with grade 2 glioma exhibit highly variable survival. Re-irradiation for recurrent disease has limited mature clinical data. We report treatment results of pulsed reduced dose rate (PRDR) radiation for patients with recurrent grade 2 glioma. METHODS A retrospective analysis of 58 patients treated with PRDR from 2000-2021 was performed. Radiation was delivered in 0.2 Gy pulses every three minutes encompassing tumor plus margin. Survival outcomes and prognostic factors on outcome were Kaplan Meier and Cox regression analyses. RESULTS The median survival from date of initial surgery was 8.6 years (95% CI 5.5-11.8 yrs). 69% of patients showed malignant transformation to grade 3 (38%) or grade 4 (31%) glioma. Overall survival following PRDR was 12.6 months (95% CI 8.3-17.0 mo) and progression free survival was 6.2 months (95% CI 3.8-8.6 mo). Overall response rate based on post PRDR MRI was 36%. In patients who maintained grade 2 histology at recurrence, overall survival from PRDR was 22.0 months with five patients remaining disease free, the longest at 8.2 and 11.4 years. PRDR was generally well tolerated. CONCLUSIONS To our knowledge, this is the largest reported series of patients with recurrent grade 2 gliomas treated with PRDR radiation for disease recurrence. We demonstrate promising survival and acceptable toxicity profiles following re-irradiation. In the cohort of patients who maintain grade 2 disease, prolonged survival (&amp;gt;5 years) is observed in selected patients. For the entire cohort, 1p19q co-deletion, KPS, and longer time from initial diagnosis to PRDR were associated with improved survival.

4Din vivodosimetry for a FLASH electron beam using radiation-induced acoustic imaging.

&#xD;The primary goal of this research is to demonstrate the feasibility of radiation-induced acoustic imaging (RAI) as a volumetric dosimetry tool for ultra-high dose rate FLASH electron radiotherapy (FLASH-RT) in real time. This technology aims to improve patient outcomes by accurate measurements of in vivo dose delivery to target tumor volumes.&#xD;Approach:&#xD;The study utilized the FLASH-capable eRT6 LINAC to deliver electron beams under various doses (1.2 Gy/pulse to 4.95 Gy/ pulse) and instantaneous dose rates (1.55×105 Gy/s to 2.75×106 Gy/s), for imaging the beam in water and in a rabbit cadaver with RAI. A custom 256-element matrix ultrasound array was employed for real-time, volumetric (4D) imaging of individual pulses. This allowed for the exploration of dose linearity by varying the dose per pulse and analyzing the results through signal processing and image reconstruction in RAI.&#xD;Main Results:&#xD;By varying the dose per pulse through changes in source-to-surface distance (SSD), a direct correlation was established between the peak-to-peak amplitudes of pressure waves captured by the RAI system and the radiochromic film dose measurements. This correlation demonstrated dose rate linearity, including in the FLASH regime, without any saturation even at an instantaneous dose rate up to 2.75×106 Gy/s. Further, the use of the 2D matrix array enabled 4D tracking of FLASH electron beam dose distributions on animal tissue for the first time.&#xD;Significance:&#xD;This research successfully shows that 4D in vivo dosimetry is feasible during FLASH-RT using a RAI system. It allows for precise spatial (~mm) and temporal (25 frames/s) monitoring of individual FLASH beamlets during delivery. This advancement is crucial for the clinical translation of FLASH-RT as enhancing the accuracy of dose delivery to the target volume the safety and efficacy of radiotherapeutic procedures will be improved.&#xD.

Influence of grandchildren on COVID-19 vaccination uptake among older adults in China: a parallel-group, cluster-randomized controlled trial.

The uptake of COVID-19 booster vaccination among older adults in China is suboptimal. Here, we report the results of a parallel-group cluster-randomized controlled trial evaluating the efficacy of promoting COVID-19 booster vaccination among grandparents (≥60 years) through a health education intervention delivered to their grandchildren (aged ≥16 years) in a Chinese cohort (Chinese Clinical Trial Registry: ChiCTR2200063240 ). The primary outcome was the uptake rate of COVID-19 booster dose among grandparents. Secondary outcomes include grandparents' attitude and intention to get a COVID-19 booster dose. A total of 202 college students were randomized 1:1 to either the intervention arm of web-based health education and 14 daily reminders (n = 188 grandparents) or control arm (n = 187 grandparents) and reported their grandparents' COVID-19 booster vaccination status at baseline and 21 days. Grandparents in the intervention arm were more likely to receive COVID-19 booster vaccination compared to control cohort (intervention, 30.6%; control, 16.9%; risk ratio = 2.00 (95% CI, 1.09 to 3.66)). Grandparents in the intervention arm also had greater attitude change (β = 0.28 (95% CI, 0.04 to 0.52)) and intention change (β = 0.32 (95% CI, 0.12 to 0.52)) to receive a COVID-19 booster dose. Our results show that an educational intervention targeting college students increased COVID-19 booster vaccination uptake among grandparents in China.

Effect of hydrogen, helium and dose rate on the evolution of dislocation loop in pure iron during in-situ ion irradiation

Simulating neutron irradiation with ion irradiation requires considering the comprehensive effects of hydrogen, helium and dose rate to fully understand the microstructure evolution of material in an irradiation environment. Here, the characterization and evolution of dislocation loops in pure iron were investigated under heavy ion irradiation with four different injected gas ion types (Fe+, Fe++H2+, Fe++He+and Fe++H2++He+) and under dual-beam (Fe++He+) irradiation with four different dose rates using in-situ transmission electron microscopy at 723 K. Comparing to the single-beam (Fe+) irradiation, the additional injection of H or He, or co-injected H and He, mainly promoted the nucleation of dislocation loops at the early stage of irradiation and enhanced loop growth after that. Among them, the simultaneous irradiation of triple beams (Fe++H2++He+) was most pronounced. Moreover, triple-beam (Fe++H2++He+) irradiation resulted in the highest ratio of the rotation of loop habit-plane. Under dual-beam (Fe++He+) irradiation, the results demonstrated that as the dose rate increased, the loop density increased and the loop size decreased. Moreover, the fraction of 〈100〉 loops at low dose rate was noticeably greater than that at high dose rate. The results of the current work provide important references for a better understanding of the effectiveness of ion irradiation in simulating neutron irradiation.

Quantifying the Growth Kinetics of Lithium Metal Reduced from Solid Ionic Conductors.

Investigating the growth kinetics of Li metal in solid-state batteries is crucial to both a fundamental understanding and practical application. Here, by directly observing the formation of Li metal from Ta-doped Li6.4La3Zr1.4Ta0.6O12 (LLZTO) in a transmission electron microscope, the growth kinetics is analyzed quantitatively. The growth kinetics of Li deposits shows a cubic-curve characteristic for LLZTO with Li-source-free. Instead, a linear growth process is observed with Li-source supplied. The impact of the illuminating electron dose rate on the growth kinetics is clarified, indicating that even low dose rates (1-3 e-/Å2/s) could affect Li growth, highlighting the significance of controlling dose rates. Furthermore, a new pathway for the formation of Li metal from Li-containing materials utilizing the field-emission effect is reported. This work has implications on the failure mechanism in solid batteries by using limited Li anodes and opens pathways for regulating Li growth in LLZTO at various scenarios, which can also extend to other ionic conductors.

Dynamic model of changes in the trophic structure of an ecosystem affected by chronic radiation exposure

The conceptual dynamic ecosystem model was developed to evaluate the self-organization of trophic structure in ecosystems during the course of biogenic succession. This model was applied to analyze the possible changes in the ecosystem under impact of the anthropogenic physical stressor – chronic exposure to ionizing irradiation. The model predicts that amount of the limiting biogenic nutrient in the environment can modify the ecological effects of ionizing radiation. Negative effects of the chronic exposure are less significant in ecosystems with high food supply. The model does not show presence of any ecological effect of radiation at the exposure rates less than the derived consideration reference levels, obtained by International Commission on Radiological Protection for individual nature organisms. If the dose rates are higher than those levels, radiation exposure can affect ecological interactions between species. The model shows that environmental hormesis can exist in the ecosystems, impacted by the chronic radiation exposure. The reason of this effect is change of the ecological coefficients (for example, decrease of the predation rate), which in the certain range of parameters leads to the increase of biomasses of all species at the same amount of the limiting biogenic nutrient in ecosystem. Trigger regimes exist in the model ecosystem with mixed-feeding consumers. Within the trigger area, the realization of a particular trophic structure depends on initial species biomasses. A hysteresis phenomenon exists in such ecosystems, which means that the successive changes in the trophic structures realized following the increase of the influencing factor are not reproduced in the same order if the influencing factor was gradually decreased back to its previous values. The model predicts for this case, that the radioactively contaminated ecosystem does not necessarily return to its initial trophic structure, despite the dose rate decreases to the initial levels.

Impact of medication dosage on Helicobacter pylori eradication rates among pediatric patients.

Helicobacter pylori rates of eradication to common first-line regimens continue to decline globally. Prescription of the appropriate medication dosage is an important consideration, particularly in the pediatric population due to medication weight-based dosing. Limited data is available on the impact of guideline-recommended weight-based dosing on the successful eradication of H. pylori in children. Retrospective study of patients with histologic evidence of H. pylori from two pediatric tertiary care centers in New England. We excluded patients who were not treated or those missing eradication data. We compared the eradication rates of patients prescribed recommended weight-based dosages, duration, and frequency of treatment with those who were not. One hundred forty-four patients were included. The overall eradication rate was 73.6% (106/144). All treatment regimens were properly prescribed for 14 days. There was a high rate of improper weight-based dosing: proton pump inhibitor (PPI) 31.2% (45/144), amoxicillin 31.7% (39/123), metronidazole (MET) 19.4% (12/62), clarithromycin (CLA) 23.9% (22/70), tetracycline 50% (6/12), bismuth 26.1% (6/23). When PPIs were properly weight-dosed, there was a 78.8% eradication rate that dropped to 62.2% with suboptimal dosing (p = 0.036, OR: 2.26, CI: 1.04-4.87). When amoxicillin was properly weight-dosed, successful eradication was achieved in 81% versus only 53.8% when improperly dosed (p = 0.002; OR: 3.64, CI: 1.58-8.37). There was no statistically significant impact on eradication rates with improper weight-based dosing of MET, CLA, tetracycline, or bismuth. Proper weight-based dosing of amoxicillin and PPI is important for the successful eradication of H. pylori among children in the New England area.

The effect of electron backscatter and charge build up in media on beam current transformer signal for ultra-high dose rate (FLASH) electron beam monitoring

Objective. Beam current transformers (BCT) are promising detectors for real-time beam monitoring in ultra-high dose rate (UHDR) electron radiotherapy. However, previous studies have reported a significant sensitivity of the BCT signal to changes in source-to-surface distance (SSD), field size, and phantom material which have until now been attributed to the fluctuating levels of electrons backscattered within the BCT. The purpose of this study is to evaluate this hypothesis, with the goal of understanding and mitigating the variations in BCT signal due to changes in irradiation conditions. Approach. Monte Carlo simulations and experimental measurements were conducted with a UHDR-capable intra-operative electron linear accelerator to analyze the impact of backscattered electrons on BCT signal. The potential influence of charge accumulation in media as a mechanism affecting BCT signal perturbation was further investigated by examining the effects of phantom conductivity and electrical grounding. Finally, the effectiveness of Faraday shielding to mitigate BCT signal variations is evaluated. Main Results. Monte Carlo simulations indicated that the fraction of electrons backscattered in water and on the collimator plastic at 6 and 9 MeV is lower than 1%, suggesting that backscattered electrons alone cannot account for the observed BCT signal variations. However, our experimental measurements confirmed previous findings of BCT response variation up to 15% for different field diameters. A significant impact of phantom type on BCT response was also observed, with variations in BCT signal as high as 14.1% when comparing measurements in water and solid water. The introduction of a Faraday shield to our applicators effectively mitigated the dependencies of BCT signal on SSD, field size, and phantom material. Significance. Our results indicate that variations in BCT signal as a function of SSD, field size, and phantom material are likely driven by an electric field originating in dielectric materials exposed to the UHDR electron beam. Strategies such as Faraday shielding were shown to effectively prevent these electric fields from affecting BCT signal, enabling reliable BCT-based electron UHDR beam monitoring.

Rapid multi-catheter segmentation for magnetic resonance image-guided catheter-based interventions.

Magnetic resonance imaging (MRI) is the gold standard for delineating cancerous lesions in soft tissue. Catheter-based interventions require the accurate placement of multiple long, flexible catheters at the target site. The manual segmentation of catheters in MR images is a challenging and time-consuming task. There is a need for automated catheter segmentation to improve the efficiency of MR-guided procedures. To develop and assess a machine learning algorithm for the detection of multiple catheters in magnetic resonance images used during catheter-based interventions. In this work, a 3D U-Net was trained to retrospectively segment catheters in scans acquired during clinical MR-guided high dose rate (HDR) prostate brachytherapy cases. To assess confidence in segmentation, multiple AI models were trained. On clinical test cases, average segmentation results were used to plan the brachytherapy delivery. Dosimetric parameters were compared to the original clinical plan. Data was obtained from 35 patients who underwent HDR prostate brachytherapy for focal disease with a total of 214 image volumes. 185 image volumes from 30 patients were used for training using a five-fold cross validation split to divide the data for training and validation. To generate confidence measures of segmentation accuracy, five trained models were generated. The remaining five patients (29 volumes) were used to test the performance of the trained model by comparison to manual segmentations of three independent observers and assessment of dosimetric impact on the final clinical brachytherapy plans. The network successfully identified 95% of catheters in the test set at a rate of 0.89s per volume. The multi-model method identified the small number of cases where AI segmentation of individual catheters was poor, flagging the need for user input. AI-based segmentation performed as well as segmentations by independent observers. Plan dosimetry using AI-segmented catheters was comparable to the original plan. The vast majority of catheters were accurately identified by AI segmentation, with minimal impact on plan outcomes. The use of multiple AI models provided confidence in the segmentation accuracy and identified catheter segmentations that required further manual assessment. Real-time AI catheter segmentation can be used during MR-guided insertions to assess deflections and for rapid planning of prostate brachytherapy.

Evaluation of lower detection limit and performance analyses related to the incident angle of X-rays and absolute dose using a triple-type dosimeter

When using a wearable active-type dosimeter for real-time dosimetry during X-ray fluoroscopic procedures, medical staff should be aware of the potential for an inaccurate exposure dose due to the large angular dependence. To address this issue, our research group has proposed a triple-type active dosimeter. With this device, the incident angle of scattered X-rays can be determined based on the signal difference between two dosimeters placed side-by-side, in which the wedge filters on the entrance windows are arranged symmetrically. In addition, the absolute dose can be determined from the central dosimeter with angular dependence correction. Although the concept of using wedge filters was proven in a previous study, the wedge filter materials have not been sufficiently studied. In this study, therefore, we sought to determine which of several materials was best suited as a wedge filter material for medical applications: aluminum (Al), titanium (Ti), or copper (Cu). We analyzed the performance of dosimeters with the different wedge filter materials in terms of estimation accuracy and lower detection limit. Using a clinical fluoroscopic system with a tube voltage of 80 kV, the scattered X-rays generated from an elliptical cylinder water phantom were measured while varying the incident direction of the X-rays from −50° to +50° in 10-degree intervals. The experimental results showed that the incident angles were properly determined when using the Ti filter, but the estimation accuracy was slightly lower when using the Al and Cu filters. The accuracy of absolute dose was evaluated from the standard deviation of the absolute dose data between −50° and +50°. As a result, the accuracies when using the Al, Ti, and Cu filters were 3.6%, 3.9%, and 5.9%, respectively. The lower detection limit when using the Cu filter showed a significantly higher value (0.50 μSv/s), but that with the Ti filter was reasonable (0.07 μSv/s). Based on these experimental evaluations, we concluded that the Ti filter would be suitable for use in a triple-type dosimeter. Finally, we investigated the expected dose rates of scattered X-rays in various interventional radiology (IVR) procedures described in the literature and determined that our dosimeter could be used for actual dose measurement.