按提交时间
按主题分类
按作者
按机构
  • Assessment of the induced radioactivity in the treatment room of the heavy‑ion medical machine in Wuwei using PHITS

    分类: 核科学技术 >> 辐射物理与技术 提交时间: 2023-05-31

    摘要: Carbon-ion radiotherapy (CIRT) offers unique physical and biological advantages over photon radiotherapy. However, some
    materials and devices in the CIRT treatment room become radioactive under bombardment by therapeutic carbon-ion beams
    due to nuclear reactions, thereby leading to possible radiation hazards to medical staff and additional and unwanted doses
    to patients. This study assessed the level of induced radioactivity in the treatment room of the Heavy-Ion Medical Machine
    (HIMM) in Wuwei. Monte Carlo simulations using PHITS were performed for a conservative case under the conditions of
    maximum beam energy and intensity provided by the HIMM facility. The geometry and configuration of Treatment Room
    2 of the HIMM facility in Wuwei were adopted. We evaluated the activation of air, the phantom, and the components of
    the beamline, such as the primary collimator (PC), ridge filter (RF), and multileaf collimator (MLC). For air activation,
    we calculated the medical staff immersion external exposure and inhalation internal exposure caused by the corresponding
    radionuclides. For phantom activation, we estimated the additional dose to the patient’s family members owing to secondary
    photons after treatment. In addition, the exemption or non-exemption of the component material activation was assessed.
    The results showed that external radiation caused by air activation was the main source of the annual effective dose at
    approximately 0.5 mSv/y. The induced radioactivity exposure to family members of a patient after CIRT was approximately
    40 μSv, sufficiently lower than the public dose limit of 1 mSv/a. The induced radioactivity of the PC, RF, and MLC was all
    above the exempt levels after the devices were retired, whereas the induced radioactivity of the RS and compensator could
    reach the exempt levels after one patient session. Our study indicated that medical staff engaged in CIRT should stay away
    from the high-dose-rate area of induced radioactivity along the beam direction, shorten the residence time in the treatment
    room as much as possible, and store the activated components in isolation after the equipment is out of use. Thus, this study
    provides guidance for accurately assessing the level of induced radioactivity in the treatment room for CIRT.

  • Normalized Glandular Dose Coefficients for Digital Breast Tomosynthesis with the Chinese Detailed Breast Models

    分类: 核科学技术 >> 辐射防护技术 提交时间: 2023-11-20

    摘要: Objective: The increasing incidence of breast cancer among Chinese women has necessitated the utilization of breast X-ray screening, which carries radiation risk. This work aims to provide a dosimetry protocol for the Chinese female population, to replace the traditional standard that utilize simplified breast models, for the accurate estimation of patients’ mean glandular dose undergoing digital breast tomosynthesis (DBT).
    Approach: We have constructed the first set of Chinese female detailed breast models with their representative breast parameters. Considering the backscatter radiation and computational efficiency, we improved the combination of these models and the Chinese reference adult female whole-body voxel phantom. The image acquisition for four commercial DBT systems, which are widely employed in China, were simulated using the Monte Carlo method to obtain the normalized glandular dose coefficients of DBT (D_gN^DBT) and glandular depth dose (Dgdepz ) for different breast characteristics and X-ray spectra.
    Main results: We calculated a series of D_gN^DBT  for breasts with different percentage mass glandularity (5%, 25%, 50%, 75%, and 100%) and compressed breast thicknesses (2cm, 3cm, 4cm, 5cm, 6cm, 7cm), at various tube potentials (25kV, 28kV, 30kV, 32kV, 35kV, and 49kV) and target/filter combinations (W/Rh, W/Al, Mo/Mo, Rh/Rh, Rh/Ag). The parameter dependence of breast characteristics and beam conditions on D_gN^DBT  of detailed breast models were investigated. The D_gN^DBT results were 14.6% - 51.0% lower than those of the traditional dosimetry standard in China. The difference in D_gN^DBT was mainly due to the decrease in the depth of the main energy deposition area caused by glandular distribution along the depth direction.
    Significance: The results obtained in this work could be employed for the improvement of breast dosimetry in China, and provide more detailed information about risk assessment undergoing DBT.
     

  • THUDosePD: a three-dimensional Monte Carlo platform for phantom dose assessment

    分类: 物理学 >> 核物理学 提交时间: 2023-10-23

    摘要: Monte Carlo simulations are frequently utilized in radiation dose assessments. However, many researchers find the prevailing computing platforms to be intricate. This highlights a pressing need for a specialized framework for phantom dose evaluation. To address this gap, we developed a user-friendly radiation dose assessment platform using the Monte Carlo toolkit, Geant4. The Tsinghua University Phantom Dose (THUDosePD) augments the flexibility of Monte Carlo simulations in dosimetric research. Originating from THUDose, a code with generic, functional, and application layers, THUDosePD focuses predominantly on anatomical phantom dose assessment. Additionally, it enables medical exposure simulation, intricate geometry creation, and supports both three-dimensional radiation dose analysis and phantom format transformations. The system operates on a multi-threaded parallel CPU architecture, with some modules enhanced for GPU parallel computing. Benchmark tests on the ICRP reference male illustrated the capabilities of THUDosePD in phantom dose assessment, covering the effective dose, three-dimensional dose distribution, and three-dimensional organ dose. We also conducted a voxelization conversion on the polygon mesh phantom, demonstrating the method’s efficiency and consistency. Extended applications based on THUDosePD further underline its broad adaptability. This intuitive, three-dimensional platform stands out as a valuable tool for phantom radiation dosimetry research.

  • Comparison between 4D Robust Optimization Methods for Carbon-Ion Treatment Planning

    分类: 核科学技术 >> 核科学与技术 提交时间: 2023-08-27

    摘要: Intensity-modulated particle therapy (IMPT) with carbon ions is comparatively susceptible to various uncertainties caused by breathing motion, including range, setup, and target positioning uncertainties. To determine relative biological effectiveness-weighted dose (RWD) distributions that are resilient to these uncertainties, the reference phase-based four-dimensional (4D) robust optimization (RP-4DRO) and each phase-based 4D robust optimization (EP-4DRO) method in carbon-ion IMPT treatment planning were evaluated and compared. Based on RWD distributions, 4DRO methods were compared with 4D conventional optimization using planning target volume (PTV) margins (PTV-based optimization) to assess the effectiveness of the robust optimization methods. Carbon-ion IMPT treatment planning was conducted in a cohort of five lung cancer patients. The results indicated that the EP-4DRO method provided better robustness (P=0.080) and improved plan quality (P=0.225) for the clinical target volume (CTV) in the individual respiratory phase when compared with the PTV-based optimization. Compared with the PTV-based optimization, the RP-4DRO method ensured the robustness (P = 0.022) of the dose distributions in the reference breathing phase, albeit with a slight sacrifice of the target coverage (P=0.450). Both 4DRO methods successfully maintained the doses delivered to the organs at risk (OARs) below tolerable levels, which were lower than the doses in the PTV-based optimization (P<0.05). Furthermore, the RP-4DRO method exhibited significantly superior performance when compared with the EP-4DRO method in enhancing overall OAR sparing in either the individual respiratory phase or reference respiratory phase (P<0.05). In general, both 4DRO methods outperformed the PTV-based optimization in terms of OAR sparing and robustness.

  • Effectiveness assessment of using riverine water eDNA to simultaneously monitor the riverine and riparian biodiversity information

    分类: 生物学 >> 生态学 提交时间: 2023-07-06

    摘要: 近年来,环境DNA技术在生态学研究中的应用日益广泛。基于自然径流驱动的流域生态系统过程,利用水体环境DNA,可以实现以下游样点监测上游河段生物组成状况,以及以水体样点监测汇水区内生物组成状况,但监测的有效度尚缺乏系统验证,影响了其应用的可信度。为了研究水体环境DNA分析在流域生态系统生物多样性监测中的有效度,我们以流域生物信息流为分析框架来探讨上述水体环境DNA监测应用的两种类型及其有效度。我们以青海湖主要入湖河流——沙柳河为研究区域,用环境DNA技术对河流水体微生物组成和岸带土壤微生物组成进行了对比分析。结果显示,(1)利用下游环境DNA监测上游微生物生物多样性的有效度主要受温度和流量影响,春季的监测有效度较低(上游1公里处的生物只有76%左右可被监测到),夏秋季的监测有效度较高(上游1公里处的生物有大于96%可被监测到);(2)利用水体环境DNA监测水系汇水区内陆地微生物生物多样性的有效度主要受季节和降雨影响,春季的监测有效度较低(相邻岸带土壤中的生物只有17%左右被监测到),夏秋季的监测有效度较高(相邻岸带土壤中的生物被监测到的比例可超过62%)。由此提出,(1)以下游样点监测上游生物多样性,夏秋繁殖季是费效比最好的监测期,春季的监测样点应适当增加密度;(2)以水体样点监测陆地生物多样性,夏秋季生物活动活跃期的降雨天及雨后水浊时是费效比最好的监测期,但检测有效度的问题值得一直关注。

  • Identification of Glycoproteins Containing Specific Glycans Using a Lectin-Chemical Method

    分类: 生物学 >> 生物物理学 提交时间: 2016-05-11

    摘要: Glycosylation is one of the most common protein modifications. Each glycoprotein can be glycosylated at multiple glycosites, and each glycosites can be modified by different glycans. Due to this heterogeneity of glycosylation, it has proven difficult to study the structure-function relationship of specific glycans and their affected glycoproteins. Here, we report a novel method for rapid and quantitative identification of glycoproteins containing specific glycans. Lectin affinity isolations are followed by chemical immobilization of the captured glycopeptides, allowing the identification of glycoproteins containing specific glycans by subsequent mass spectrometry. The application of the method should be useful to facilitate our understanding of how changes in glycan associate with diseases, and to discover novel glycoproteins with certain glycans that could serve as biomarkers or therapeutic targets.

  • Structural Basis of the Differential Function of the Two C. elegans Atg8 Homologs, LGG-1 and LGG-2, in Autophagy

    分类: 生物学 >> 生物物理学 >> 生物物理、生物化学与分子生物学 提交时间: 2016-05-15

    摘要: Multicellular organisms have multiple homologs of the yeast ATG8 gene, but the differential roles of these homologs in autophagy during development remain largely unknown. Here we investigated structure/function relationships in the two C. elegans Atg8 homologs, LGG-1 and LGG-2. lgg-1 is essential for degradation of protein aggregates, while lgg-2 has cargo-specific and developmental-stage-specific roles in aggregate degradation. Crystallography revealed that the N-terminal tails of LGG-1 and LGG-2 adopt the closed and open form, respectively. LGG-1 and LGG-2 interact differentially with autophagy substrates and Atg proteins, many of which carry a LIR motif. LGG-1 and LGG-2 have structurally distinct substrate binding pockets that prefer different residues in the interacting LIR motif, thus influencing binding specificity. Lipidated LGG-1 and LGG-2 possess distinct membrane tethering and fusion activities, which may result from the N-terminal differences. Our study reveals the differential function of two ATG8 homologs in autophagy during C. elegans development.