Neuro-Oncologic Veterinary Trial for the Clinical Transfer of Microbeam Radiation Therapy: Acute to Subacute Radiotolerance after Brain Tumor Irradiation in Pet Dogs.

Synchrotron Microbeam Radiation Therapy (MRT) has repeatedly proven its superiority compared with conventional radiotherapy for glioma control in preclinical research. The clinical transfer phase of MRT has recently gained momentum; seven dogs with suspected glioma were treated under clinical conditions to determine the feasibility and safety of MRT. We administered a single fraction of 3D-conformal, image-guided MRT. Ultra-high-dose rate synchrotron X-ray microbeams (50 µm-wide, 400 µm-spaced) were delivered through five conformal irradiation ports. The PTV received ~25 Gy peak dose (within microbeams) per port, corresponding to a minimal cumulated valley dose (diffusing between microbeams) of 2.8 Gy. The dogs underwent clinical and MRI follow-up, and owner evaluations. One dog was lost to follow-up. Clinical exams of the remaining six dogs during the first 3 months did not indicate radiotoxicity induced by MRT. Quality of life improved from 7.3/10 [±0.7] to 8.9/10 [±0.3]. Tumor-induced seizure activity decreased significantly. A significant tumor volume reduction of 69% [±6%] was reached 3 months after MRT. Our study is the first neuro-oncologic veterinary trial of 3D-conformal Synchrotron MRT and reveals that MRT does not induce acute to subacute radiotoxicity in normal brain tissues. MRT improves quality of life and leads to remarkable tumor volume reduction despite low valley dose delivery. This trial is an essential step towards the forthcoming clinical application of MRT against deep-seated human brain tumors.

Efficient Modeling of Single Event Transient Effect with Limited Peak Current: Implications for Logic Circuits.

The problem that the conventional double-exponential transient current model (DE model) can overdrive the circuit, which leads to the overestimation of the soft error rate of the logic cell, is solved. Our work uses a new and accurate model for predicting the soft error rate that brings the soft error rate closer to the actual. The piecewise double-exponential transient current model (PDE model) is chosen, and the accuracy of the model is reflected using the Layout Awareness Single Event Multi Transients Soft Error Rate Calculation tool (LA-SEMT-SER tool). The model can characterize transient current pulses piecewise and limit the peak current magnitude to not exceed the conduction current. TCAD models are constructed from 28 nm process library and cell layouts. The transfer characteristic curves of devices are calibrated, and functional timing verification is performed to ensure the accuracy of the TCAD model. The experimental results show that the PDE model is not only more consistent with TCAD simulation than the DE model in modeling the single event transient currents of the device, but also that the SER calculated by the LA-SEMT-SER tool based on the PDE model has a smaller error than the SER calculated by the LA-SEMT-SER tool based on the DE model.

Controlled CMS Data Demonstrates a Cost and Clinical Advantage for Hyperbaric Oxygen for Radiation Cystitis.

Introduction: Increasing cancer survivorship, in part due to new radiation treatments, has created a larger population at risk for delayed complications of treatment. Radiation cystitis continues to occur despite targeted radiation techniques. Materials and Methods: To investigate value-based care applying hyperbaric oxygen (HBO2) to treat delayed radiation cystitis, we reviewed public-access Medicare data from 3,309 patients from Oct 1, 2014, through Dec 31, 2019. Using novel statistical modeling, we compared cost and clinical effectiveness in a hyperbaric oxygen group to a control group receiving conventional therapies. Results: Treatment in the hyperbaric group provided a 36% reduction in urinary bleeding, a 78% reduced frequency of blood transfusion for hematuria, a 31% reduction in endoscopic procedures, and fewer hospitalizations when study patients were compared to control. There was a 53% reduction in mortality and reduced unadjusted Medicare costs of $5,059 per patient within the first year after completion of HBO2 treatment per patient. When at least 40 treatments were provided, cost savings per patient increased to $11,548 for the HBO2 study group compared to the control group. This represents a 37% reduction in Medicare spending for the HBO2-treated group. We also validate a dose-response curve effect with a complete course of 40 or more HBO2 treatments having better clinical outcomes than those treated with fewer treatments. Conclusion: These data support previous studies that demonstrate clinical benefits now with cost- effectiveness when adjunctive HBO2 treatments are added to routine interventions. The methodology provides a comparative group selected without bias. It also provides validation of statistical modeling techniques that may be valuable in future analysis, complementary to more traditional methods.

Efficacy of radiation attenuating caps in reducing radiation doses received at the cerebral level in interventional physicians: a systematic review.

Background.Anecdotal reports are appearing in the scientific literature about cases of brain tumors in interventional physicians who are exposed to ionizing radiation. In response to this alarm, several designs of leaded caps have been made commercially available. However, the results reported on their efficacy are discordant.Objective.To synthesize, by means of a systematic review of the literature, the capacity of decreasing radiation levels conferred by radiation attenuating devices (RADs) at the cerebral level of interventional physicians.Methodology.A systematic review was performed including the following databases: MEDLINE, SCOPUS, EBSCO, Science Direct, Cochrane Controlled Trials Register (CENTRAL), WOS, WHO International Clinical Trials Register, Scielo and Google Scholar, considering original studies that evaluated the efficacy of RAD in experimental or clinical contexts from January 1990 to May 2023. Data selection and extraction were performed in triplicate, with a fourth author resolving discrepancies.Results.Twenty articles were included in the review from a total of 373 studies initially selected from the databases. From these, twelve studies were performed under clinical conditions encompassing 3801 fluoroscopically guided procedures, ten studies were performed under experimental conditions with phantoms, with a total of 88 procedures, four studies were performed using numerical calculations with a total of 63 procedures. The attenuation and effectiveness of provided by the caps analyzed in the present review varying from 12.3% to 99.9%, and 4.9% to 91% respectively.Conclusion.RAD were found to potentially provide radiation protection, but a high heterogeneity in the shielding afforded was found. This indicates the need for local assessment of cap efficiency according to the practice.

Hydrogen isotope population near dislocations in zirconium from molecular dynamics.

Performance of zirconium tritides used for hydrogen isotope storage is significantly changed under reactor environments. This can be attributed to the formation of various radiation-induced dislocations. To help gain insight, molecular dynamics simulations have been employed to investigate hydrogen isotope population in zirconium containing different types of edge dislocations. Our studies reveal that hydrogen isotope concentration is highest near the tensile side of dislocation cores and varies based on dislocation type. This increase in hydrogen isotope concentration can be explained by the Boltzmann equation based on calculations using swelling volume and pressure field, with significantly reduced computational cost. Strikingly, because hydrogen isotope in the compressive regions of dislocations is depleted, the overall hydrogen isotope content is found to be unchanged by dislocation formation. These results counter the previous view that the dislocation trapping effect increases hydrogen isotope solubility and provide an understanding of changes in hydrogen isotope pressure under reactor conditions. By elucidating the impact of dislocations on hydrogen isotope storage performance, this research offers insights for optimizing zirconium tritides in nuclear applications. and contributes to the advancement of hydrogen isotope storage materials.

The effects of high-dose radiation therapy on bone: a scoping review.

PURPOSE: This scoping review presents the preclinical and clinical data on the effects of high-dose radiation therapy (RT) on bone structure and function. MATERIALS AND METHODS: An extensive PubMed search was performed for the relevant questions. The data were then synthesized into a comprehensive summary of the available relevant in-vitro, preclinical and clinical literature. RESULTS: In-vitro studies of high-dose RT on cell cultures show considerable damage in the viability and functional capacity of the primary cells of the bones; the osteoclasts, the osteoblasts, and the osteocytes. In-vivo animal models show that high-dose RT induces significant morphological changes to the bone, inhibits the ability of bone to repair damage, and increases the fragility of the bone. Clinical data show that there is an increasing risk over time of damage to the bone, such as fractures, after high-dose RT. CONCLUSION: These findings suggest that there may be a limit to the safe dose for single-fraction RT, and the long-term consequences of high-dose RT for the patients must be considered.

A Machine Learning Approach to Predict Radiation Effects in Microelectronic Components.

This paper presents an innovative technique, Advanced Predictor of Electrical Parameters, based on machine learning methods to predict the degradation of electronic components under the effects of radiation. The term degradation refers to the way in which electrical parameters of the electronic components vary with the irradiation dose. This method consists of two sequential steps defined as 'recognition of degradation patterns in the database' and 'degradation prediction of new samples without any kind of irradiation'. The technique can be used under two different approaches called 'pure data driven' and 'model based'. In this paper, the use of Advanced Predictor of Electrical Parameters is shown for bipolar transistors, but the methodology is sufficiently general to be applied to any other component.

Modalidades de radioterapia empregadas para o câncer de cabeça e pescoço / Radiotherapy modalities used for head and neck cancer

O câncer de cabeça e pescoço (CCP) refere-se ao grupo de tumores que atingem a laringe, cavidade nasal, nasofaringe, orofaringe, cavidade oral e glândulas salivares. A radioterapia no paciente com CCP representa uma terapia para manutenção do órgão, através da destruição das células neoplásicas malignas. O objetivo do presente estudo foi identificar estratégias radioterápicas aplicadas ao paciente com CCP e seus respectivos efeitos colaterais em cavidade oral, além de investigar as principais modalidades utilizadas nos sistemas de saúde do Brasil. Tratou-se de uma revisão narrativa da literatura com busca ativa das bases eletrônicas PUBMED, LILACS e SCIELO. Após todas as etapas de refinamento, um total de 58 artigos foram incluídos na presente revisão. A radioterapia possui papel de destaque no tratamento do CCP. No entanto, por não ser um método terapêutico com alta especificidade, resulta em efeitos adversos ao tratamento como mucosite oral, trismo e disfunção salivar, que findam por reduzir a qualidade de vida do paciente. Dentre as principais técnicas radioterapêuticas utilizadas no Brasil, a IMRT e VMAT caracterizam-se como as formas mais avançadas da terapia em 3D, proporcionando doses equivalentes para cada área da lesão tumoral, poupando áreas teciduais circunvizinhas que não necessitam de irradiação. Além da toxicidade reduzida, uma maior sobrevida pode ser observada em pacientes tratados com essas técnicas. Um dos maiores desafios atuais na radioterapia contra o CCP é a proteção de tecidos saudáveis. Nesse sentido, a IMRT e VMAT apresentam superioridade em relação às demais técnicas.

Head and neck cancer (CCP) refers to the group of tumors that affect the larynx, nasal cavity, nasopharynx, oropharynx, oral cavity and salivary glands. Radiotherapy in patients with CCP represents a therapy for organ maintenance, through the destruction of malignant neoplastic cells. The aim of this study was to identify radiotherapy strategies applied to patients with CCP and their respective side effects in the oral cavity, and to investigate the main modalities used in health systems in Brazil. It was a narrative review of the literature with active search of electronic databases PUBMED, LILACS and SCIELO. After all stages of refinement, a total of 58 articles were included in this review. Radiotherapy has a prominent role in the treatment of CCP. However, because it is not a therapeutic method with high specificity, it results in adverse effects to treatment such as oral mucositis, trismus and salivary dysfunction, which end up reducing the quality of life of the patient. Among the main radiotherapeutic techniques used in Brazil, IMRT and VMAT are characterized as the most advanced forms of 3D therapy, providing equivalent doses for each area of the tumor sparing surrounding tissue areas that do not require irradiation. In addition to reduced toxicity, greater survival can be observed in patients treated with these techniques. One of the biggest current challenges in radiation therapy against CCP is the protection of healthy tissues. In this sense, the IMRT and VMAT present superiority in relation to the other techniques.

Cardiac substructure delineation in radiation therapy - A state-of-the-art review.

Delineation of cardiac substructures is crucial for a better understanding of radiation-related cardiotoxicities and to facilitate accurate and precise cardiac dose calculation for developing and applying risk models. This review examines recent advancements in cardiac substructure delineation in the radiation therapy (RT) context, aiming to provide a comprehensive overview of the current level of knowledge, challenges and future directions in this evolving field. Imaging used for RT planning presents challenges in reliably visualising cardiac anatomy. Although cardiac atlases and contouring guidelines aid in standardisation and reduction of variability, significant uncertainties remain in defining cardiac anatomy. Coupled with the inherent complexity of the heart, this necessitates auto-contouring for consistent large-scale data analysis and improved efficiency in prospective applications. Auto-contouring models, developed primarily for breast and lung cancer RT, have demonstrated performance comparable to manual contouring, marking a significant milestone in the evolution of cardiac delineation practices. Nevertheless, several key concerns require further investigation. There is an unmet need for expanding cardiac auto-contouring models to encompass a broader range of cancer sites. A shift in focus is needed from ensuring accuracy to enhancing the robustness and accessibility of auto-contouring models. Addressing these challenges is paramount for the integration of cardiac substructure delineation and associated risk models into routine clinical practice, thereby improving the safety of RT for future cancer patients.

Predictive factors for radiation-induced pituitary damage in pediatric patients with brain tumors.

BACKGROUND AND PURPOSE: Multiple studies demonstrated hypothalamic-pituitary dysfunction in survivors of pediatric brain tumors. However, few studies investigated the trajectories of pituitary height in these patients and their associations with pituitary function. We aimed to evaluate longitudinal changes of pituitary height in children and adolescents with brain tumors, and their association with endocrine deficiencies. MATERIALS AND METHODS: We conducted a retrospective analysis of 193 pediatric patients (54.9% male) diagnosed with brain tumors from 2002 to 2018, with a minimum of two years of radiological follow-up. Pituitary height was measured using MRI scans at diagnosis and at 2, 5, and 10 years post-diagnosis, with clinical data sourced from patient charts. RESULTS: Average age at diagnosis was 7.6 ± 4.5 years, with a follow-up of 6.1 ± 3.4 years. 52.8% underwent radiotherapy and 37.8% experienced pituitary hormone deficiency. Radiation treatment was a significant predictor of decreased pituitary height at all observed time points (p = 0.016, p < 0.001, p = 0.008, respectively). Additionally, chemotherapy (p = 0.004) or radiotherapy (p = 0.022) history and pituitary height at 10 years (p = 0.047) were predictors of endocrine deficiencies. ANOVA revealed an expected increase in pituitary height over time in pediatric patients, but this growth was significantly impacted by radiation treatment and gender (p for interaction = 0.005 and 0.025, respectively). CONCLUSION: Cranial irradiation in pediatric patients is associated with impairment of the physiologic increase in pituitary size; in turn, decreased pituitary height is associated with endocrine dysfunction. We suggest that pituitary gland should be evaluated on surveillance imaging of pediatric brain tumor survivors, and if small for age, clinical endocrine evaluation should be pursued.

In vitro study of radiosensitivity in colorectal cancer cell lines associated with Lynch syndrome.

Introduction: Lynch syndrome patients have an inherited predisposition to cancer due to a deficiency in DNA mismatch repair (MMR) genes which could lead to a higher risk of developing cancer if exposed to ionizing radiation. This pilot study aims to reveal the association between MMR deficiency and radiosensitivity at both a CT relevant low dose (20 mGy) and a therapeutic higher dose (2 Gy). Methods: Human colorectal cancer cell lines with (dMMR) or without MMR deficiency (pMMR) were analyzed before and after exposure to radiation using cellular and cytogenetic analyses i.e., clonogenic assay to determine cell reproductive death; sister chromatid exchange (SCE) assay to detect the exchange of DNA between sister chromatids; γH2AX assay to analyze DNA damage repair; and apoptosis analysis to compare cell death response. The advantages and limitations of these assays were assessed in vitro, and their applicability and feasibility investigated for their potential to be used for further studies using clinical samples. Results: Results from the clonogenic assay indicated that the pMMR cell line (HT29) was significantly more radio-resistant than the dMMR cell lines (HCT116, SW48, and LoVo) after 2 Gy X-irradiation. Both cell type and radiation dose had a significant effect on the yield of SCEs/chromosome. When the yield of SCEs/chromosome for the irradiated samples (2 Gy) was normalized against the controls, no significant difference was observed between the cell lines. For the γH2AX assay, 0, 20 mGy and 2 Gy were examined at post-exposure time points of 30 min (min), 4 and 24 h (h). Statistical analysis revealed that HT29 was only significantly more radio-resistant than the MLH1-deficient cells lines, but not the MSH2-deficient cell line. Apoptosis analysis (4 Gy) revealed that HT29 was significantly more radio-resistant than HCT116 albeit with very few apoptotic cells observed. Discussion: Overall, this study showed radio-resistance of the MMR proficient cell line in some assays, but not in the others. All methods used within this study have been validated; however, due to the limitations associated with cancer cell lines, the next step will be to use these assays in clinical samples in an effort to understand the biological and mechanistic effects of radiation in Lynch patients as well as the health implications.

Impact on the Transcriptome of Proton Beam Irradiation Targeted at Healthy Cardiac Tissue of Mice.

Proton beam therapy is considered a step forward with respect to electromagnetic radiation, thanks to the reduction in the dose delivered. Among unwanted effects to healthy tissue, cardiovascular complications are a known long-term radiotherapy complication. The transcriptional response of cardiac tissue from xenografted BALB/c nude mice obtained at 3 and 10 days after proton irradiation covering both the tumor region and the underlying healthy tissue was analyzed as a function of dose and time. Three doses were used: 2 Gy, 6 Gy, and 9 Gy. The intermediate dose had caused the greatest impact at 3 days after irradiation: at 2 Gy, 219 genes were differently expressed, many of them represented by zinc finger proteins; at 6 Gy, there were 1109, with a predominance of genes involved in energy metabolism and responses to stimuli; and at 9 Gy, there were 105, mainly represented by zinc finger proteins and molecules involved in the regulation of cardiac function. After 10 days, no significant effects were detected, suggesting that cellular repair mechanisms had defused the potential alterations in gene expression. The nonlinear dose-response curve indicates a need to update the models built on photons to improve accuracy in health risk prediction. Our data also suggest a possible role for zinc finger protein genes as markers of proton therapy efficacy.

Safety evaluation of sinus patency after stereotactic radiosurgery for transverse-sigmoid sinus dural arteriovenous fistulas: implications of treatment options for patients with Borden type I fistulas.

OBJECTIVE: This study aimed to assess the efficacy and safety of stereotactic radiosurgery (SRS) in treating transverse-sigmoid sinus dural arteriovenous fistulas (TSS DAVFs), and to investigate post-SRS sinus patency, focusing on the risk factors associated with treated sinus occlusion. METHODS: Data from 34 patients treated with SRS between January 2006 and April 2023 were analyzed. Detailed angioarchitecture was confirmed using digital subtraction angiography before SRS. Angiography of the ipsilateral internal carotid artery and vertebral artery was performed to evaluate whether the involved side of the TSS was used for normal venous drainage. TSS stenosis was defined as sinus diameter < 50% of the normal proximal diameter. DAVF shunt obliteration, TSS occlusion, neurological status, and adverse events were also evaluated. RESULTS: Of the 34 patients, 21 had Borden type I and 14 had Borden type II DAVFs. The median age at SRS was 64 years (interquartile range 54-71 years), and the follow-up period was 31 months (interquartile range 15-94 months). Complete shunt obliteration was achieved in 24 (70.6%) patients. The cumulative 2-, 3-, and 5-year shunt obliteration rates were 49.6%, 71.2%, and 86.0%, respectively. Borden type I had higher obliteration rates (60.5%, 83.1%, and 94.4%, respectively) than Borden type II (41.7%, 51.4%, and 75.7%, respectively; p = 0.034). TSS occlusion occurred in 5 patients (14.7%). The cumulative 1-, 5-, and 10-year TSS occlusion rates were 2.9%, 8.3%, and 23.6%, respectively, across the entire cohort. All occlusions occurred exclusively in the sinuses that were not used for normal venous drainage. Cox proportional analyses revealed that TSS stenosis and the sinus not being used for normal venous drainage were significantly associated with a greater risk of TSS occlusion after SRS (HR 9.44, 95% CI 1.01-77.13; p = 0.049). CONCLUSIONS: SRS is effective and safe for TSS DAVF and results in favorable shunt obliteration, symptom improvement, and low complication rates. TSS occlusion after SRS is asymptomatic and is limited to sinuses that are not used for normal venous drainage.

Pathologic features of brain hemorrhage after radiation treatment: case series with somatic mutation analysis.

BACKGROUND: Radiation treatment for diseases of the brain can result in hemorrhagic adverse radiation effects. The underlying pathologic substrate of brain bleeding after irradiation has not been elucidated, nor potential associations with induced somatic mutations. METHODS: We retrospectively reviewed our department's pathology database over 5 years and identified 5 biopsy specimens (4 patients) for hemorrhagic lesions after brain irradiation. Tissues with active malignancy were excluded. Samples were characterized using H&E, Perl's Prussian Blue, and Masson's Trichrome; immunostaining for B-cells (anti-CD20), T-cells (anti-CD3), endothelium (anti-CD31), macrophages (anti-CD163), α-smooth muscle actin, and TUNEL. DNA analysis was done by two panels of next-generation sequencing for somatic mutations associated with known cerebrovascular anomalies. RESULTS: One lesion involved hemorrhagic expansion among multifocal microbleeds that had developed after craniospinal irradiation for distant medulloblastoma treatment. Three bleeds arose in the bed of focally irradiated arteriovenous malformations (AVM) after confirmed obliteration. A fifth specimen involved the radiation field distinct from an irradiated AVM bed. From these, 2 patterns of hemorrhagic vascular pathology were identified: encapsulated hematomas and cavernous-like malformations. All lesions included telangiectasias with dysmorphic endothelium, consistent with primordial cavernous malformations with an associated inflammatory response. DNA analysis demonstrated genetic variants in PIK3CA and/or PTEN genes but excluded mutations in CCM genes. CONCLUSIONS: Despite pathologic heterogeneity, brain bleeding after irradiation is uniformly associated with primordial cavernous-like telangiectasias and disruption of genes implicated in dysangiogenesis but not genes implicated as causative of cerebral cavernous malformations. This may implicate a novel signaling axis as an area for future study.

0.263 terahertz irradiation induced genes expression changes in Caenorhabditis elegans.

The biosafety of terahertz (THz) waves has emerged as a new area of concern with the gradual application of terahertz radiation. Even though many studies have been conducted to investigate the influence of THz radiation on living organisms, the biological effects of terahertz waves have not yet been fully revealed. In this study, Caenorhabditis elegans (C. elegans) was used to evaluate the biological consequences of whole-body exposure to 0.263 THz irradiation. The integration of transcriptome sequencing and behavioral tests of C. elegans revealed that high-power THz irradiation damaged the epidermal ultrastructures, inhibited the expression of the cuticle collagen genes, and impaired the movement of C. elegans. Moreover, the genes involved in the immune system and the neural system were dramatically down-regulated by high-power THz irradiation. Our findings offer fresh perspectives on the biological impacts of high-power THz radiation that could cause epidermal damage and provoke a systemic response.

Evaluation of risks of cardiovascular disease from radiation exposure linked to computed tomography scans in the UK.

Epidemiological studies of patient populations have shown that high doses of radiation increase risks of cardiovascular disease (CVD). Results from a recent meta-analysis of 93 epidemiological studies covering a wide range of doses provided evidence of a causal association between radiation exposure and CVD, and indicated excess relative risk per Gy for maximum dose below 500 mGy or delivered at low dose rates. These doses cover the range of organ doses expected from multiple diagnostic computed tomography (CT) scans. Dose-effect factors for the excess absolute risk of mortality from CVD following radiation exposure were derived from the meta-analysis. The present study uses these factors to estimate excess risks of mortality for various types of CVD, including cerebrovascular disease (CeVD), from CT scans of the body and head, assuming that the meta-analytic factors were accurate and represented a causal relationship. Estimates are based on cumulative doses to the heart and brain from CT scans performed on 105 574 patients on 12 CT scanners over a period of 5½ years. The results suggest that the excess number of deaths from CeVD could be 7 or 26 per 100 000 patients depending whether threshold brain doses of 200 mGy or 50 mGy, respectively are assumed. These results could have implications for head CT scans. However, the results rely on the validity of risk factors derived in the meta-analysis informing this assessment and which include significant uncertainties. Further incidence studies should provide better information on risk factors and dose thresholds, particularly for CeVD following head CT scans.

Interplay of immune modulation, adaptive response and hormesis: Suggestive of threshold for clinical manifestation of effects of ionizing radiation at low doses?

The health impacts of low-dose ionizing radiation exposures have been a subject of debate over the last three to four decades. While there has been enough evidence of "no adverse observable" health effects at low doses and low dose rates, the hypothesis of "Linear No Threshold" continues to rule and govern the principles of radiation protection and the formulation of regulations and public policies. In adopting this conservative approach, the role of the biological processes underway in the human body is kept at abeyance. This review consolidates the available studies that discuss all related biological pathways and repair mechanisms that inhibit the progression of deleterious effects at low doses and low dose rates of ionizing radiation. It is pertinent that, taking cognizance of these processes, there is a need to have a relook at policies of radiation protection, which as of now are too stringent, leading to undue economic losses and negative public perception about radiation.

Delayed Imaging Changes 18 Months or Longer After Stereotactic Radiosurgery for Brain Metastases: Necrosis or Progression.

OBJECTIVE: Imaging changes after stereotactic radiosurgery (SRS) can occur for years after treatment, although the available data on the incidence of tumor progression and adverse radiation effects (ARE) are generally limited to the first 2 years after treatment. METHODS: A single-institution retrospective review was conducted of patients who had >18 months of imaging follow-up available. Patients who had ≥1 metastatic brain lesions treated with Gamma Knife SRS were assessed for the time to radiographic progression. Those with progression ≥18 months after the initial treatment were included in the present study. The lesions that progressed were characterized as either ARE or tumor progression based on the tissue diagnosis or imaging characteristics over time. RESULTS: The cumulative incidence of delayed imaging radiographic progression was 35% at 5 years after the initial SRS. The cumulative incidence curves of the time to radiographic progression for lesions determined to be ARE and lesions determined to be tumor progression were not significantly different statistically. The cumulative incidence of delayed ARE and delayed tumor progression was 17% and 16% at 5 years, respectively. Multivariate analysis indicated that the number of metastatic brain lesions present at the initial SRS was the only factor associated with late radiographic progression. CONCLUSIONS: The timing of late radiographic progression does not differ between ARE and tumor progression. The number of metastatic brain lesions at the initial SRS is a risk factor for late radiographic progression.

Comparison of typical radiation doses and risks using an anthropomorphic 'bone fracture' phantom for commonly performed X-ray projections in a 5-year-old.

INTRODUCTION: Diagnostic reference levels (DRLs) are typical dose levels for medical imaging examinations for groups of standard-sized patients or standard phantoms for broadly defined types of equipment used as a tool to aid optimisation of protection for medical exposures. Currently, there are no paediatric DRLs for conventional radiography (i.e. general X-rays) published in Australia. The aim of this study was to establish typical radiation doses and risks that are representative of those delivered for commonly performed X-ray projections for a 5-year-old/20 kg child using a 5-year-old anthropomorphic 'bone fracture' phantom in three dedicated paediatric radiology departments in Victoria. METHODS: A total of 20 projection images were acquired for a standard 5-year-old/20 kg phantom using digital radiography X-ray equipment. The air kerma-area product (KAP) measured at each centre by a KAP metre, which was calibrated to a national primary standard, was considered to represent the median value for that centre for each X-ray projection. Organ doses and effective dose were estimated using PCXMC software, and risks of radiation-induced cancer and radiation-induced death were calculated based on the BEIR VII report. RESULTS: The typical doses for the individual X-ray projections ranged from 3 mGy•cm2 to 86 mGy•cm2 , whilst the effective doses ranged from 0.00004 to 0.07 mSv. The radiation risks were 'minimal' to 'negligible'. CONCLUSION: The estimation of typical radiation doses and associated risks for a 5-year-old/20 kg phantom study provides reference values for guidance and is a first step in assisting optimisation at other institutions until national DRLs, based on patient data from the clinical setting, are published.

A Super-Resolution Diffusion Model for Recovering Bone Microstructure from CT Images.

Purpose: To use a diffusion-based deep learning model to recover bone microstructure from low-resolution images of the proximal femur, a common site of traumatic osteoporotic fractures. Materials and Methods: Training and testing data in this retrospective study consisted of high-resolution cadaveric micro-CT scans (n = 26), which served as ground truth. The images were downsampled prior to use for model training. The model was used to increase spatial resolution in these low-resolution images threefold, from 0.72 mm to 0.24 mm, sufficient to visualize bone microstructure. Model performance was validated using microstructural metrics and finite element simulation-derived stiffness of trabecular regions. Performance was also evaluated across a handful of image quality assessment metrics. Correlations between model performance and ground truth were assessed using intraclass correlation coefficients (ICCs) and Pearson correlation coefficients. Results: Compared with popular deep learning baselines, the proposed model exhibited greater accuracy (mean ICC of proposed model, 0.92 vs ICC of next best method, 0.83) and lower bias (mean difference in means, 3.80% vs 10.00%, respectively) across the physiologic metrics. Two gradient-based image quality metrics strongly correlated with accuracy across structural and mechanical criteria (r > 0.89). Conclusion: The proposed method may enable accurate measurements of bone structure and strength with a radiation dose on par with current clinical imaging protocols, improving the viability of clinical CT for assessing bone health.Keywords: CT, Image Postprocessing, Skeletal-Appendicular, Long Bones, Radiation Effects, Quantification, Prognosis, Semisupervised Learning Online supplemental material is available for this article. © RSNA, 2023.