辐射引起的电子自旋共振信号在回顾剂量学中的应用

辐射可以激发某些材料以及生物样品产生自由基,电子自旋共振(ESR)波谱仪可以检测到这些自由基信号,而信号的强度与受到电离辐射的剂量相关。利用牙齿的ESR波谱估算核事故的辐射剂量是一种经典的方法。近年来,很多学者研究了指(趾)甲、头发、手机屏幕等易获取材料的ESR波谱与辐射剂量的关系。该文从这些材料的背景信号、剂量学的线性关系、探测下限以及信号的稳定性等方面进行综述,以期为核事故的剂量估算提供更好的依据。     

Application of GEANT4 radiation transport toolkit to dose calculations in anthropomorphic phantoms

In this paper, we present a novel implementation of a dose calculation application, based on the GEANT4 Monte Carlo toolkit. Validation studies were performed with an homogeneous water phantom and an Alderson–Rando anthropomorphic phantom both irradiated with high-energy photon beams produced by a clinical linear accelerator. As input, this tool requires computer tomography images for automatic codification of voxel-based geometries and phase-space distributions to characterize the incident radiation field. Simulation results were compared with ionization chamber, thermoluminescent dosimetry data and commercial treatment planning system calculations. In homogeneous water phantom, overall agreement with measurements were within 1–2%. For anthropomorphic simulated setups (thorax and head irradiation) mean differences between GEANT4 and TLD measurements were less than 2%. Significant differences between GEANT4 and a semi-analytical algorithm implemented in the treatment planning system, were found in low-density regions, such as air cavities with strong electronic disequilibrium.     

用电子顺磁共振波谱拟合方法估算牙釉质辐射剂量

目的 探讨运用电子顺磁共振(electron paramagnetic resonance, EPR)波谱拟合技术估算牙釉质EPR辐射剂量的准确性。方法 编制多成分叠加型EPR粉末波谱拟合软件,分别拟合牙齿本底信号(background signal,BS)和辐照诱发信号(radiation-induced signal,RS)的EPR波谱模型,用波谱模型叠加计算方法拟合出实际辐照后牙釉质的EPR波谱,从复合谱中提取出RS成分并计算其相对强度,建立剂量响应曲线,估算样品剂量,并将剂量估算结果与传统的波谱强度测量方法进行比较。结果 拟合获得的BS信号为单峰高斯线形粉末谱,g=2.0035,线宽Hpp=0.650-1.100 mT; RS信号为轴对称多晶粉末谱线形,其g_⊥=2.0018,g_‖＝1.9965,线宽Hpp=0.335-0.400 mT;分离BS与RS后得到的RS相对强度与辐照剂量呈线性相关,剂量响应方程为:y=240.74x+76 724(R²=0.9947),剂量估算结果相对误差期望值为0.13。结论 EPR波谱拟合方法在一定程度上提高了牙釉质辐射剂量估计的准确性和可信度。     

Organ and effective dose conversion coefficients for radiographic examinations of the pediatric skull estimated by Monte Carlo methods

The objective of the present work was to provide precise effective and organ dose data for radiographic examinations of the skull performed on pediatric patients. To accomplish this, the MCNP4C2 transport code was utilized and 18 mathematical anthropomorphic phantoms, representing ages from a newborn child to a 17-year-old adolescent, were developed. Three common projections, anterior–posterior, posterior–anterior and lateral, were considered. The results consist of effective and organ radiation doses normalized to the entrance surface dose. Normalized data are presented for a wide range of peak kilovoltages and beam filtration values so that doses for any X-ray unit can be calculated. Both organ and effective dose values showed an inverse correlation with age. Good agreement was observed between the normalized effective doses produced in this study and values derived from calculations based on the National Radiological Protection Board coefficients for specific mathematical phantoms representing 1-, 5-, 10- and 15-year-old children. In the present work, dose data for nine mathematical phantoms representing 0-, 1-, 2-, 3-, 4-, 5-, 6-, 9- and 14-year-old pediatric patients were provided for estimation of organ and effective doses delivered to pediatric patients from radiographic examinations of the skull.     

Numerical signal treatment for optimized alanine/ESR dosimetry in the therapy-level dose range

Electron spin resonance (ESR) spectra of alanine detectors irradiated to absorbed doses below 5 Gy are affected by a varying non-linear background which mainly influences the lower limit of detection in alanine/ESR dosimetry. A mathematical method based on fast Fourier transform is described capable of filtering simultaneously background and noise in the frequency domain of ESR spectra. It provides clearer alanine/ESR signals down to 50 mGy. Even in non-irradiated but long-term stored alanine detectors an ESR signal could be observed similar to irradiated alanine (pre-signal). A linear ESR signal vs absorbed dose relationship was found above 200 mGy, after correction for background and pre-signal. The number of repeated ESR read-out cycles and hence the time required for a precise and reliable low-dose evaluation have significantly been reduced. The method has been worked out for the therapy-level dosimetry range and tested on a Bruker ESP 300 and for comparison Bruker EMS 104 ESR spectrometer.     

Beta-particle dosimetry in radiation synovectomy

Beta-particle dosimetry of various radionuclides used in the treatment of rheumatoid arthritis was estimated using Monte Carlo radiation transport simulation coupled with experiments using reactor-produced radionuclides and radiachromic film dosimeters inserted into joint phantoms and the knees of cadavers. Results are presented as absorbed dose factors (cGy-cm²/MBq-s) versus depth in a mathematical model of the rheumatoid joint which includes regions of bone, articular cartilage, joint capsule, and tissue (synovium) found in all synovial joints. The factors can be used to estimate absorbed dose and dose rate distributions in treated joints. In particular, guidance is provided for those interested in (a) a given radionuclide's therapeutic range, (b) the amount of radioactivity to administer on a case-by-case basis, (c) the expected therapeutic dose to synovium, and (d) the radiation dose imparted to other, nontarget components in the joint, including bone and articular cartilage.     

牙釉质ESR回顾性剂量技术与剂量重建

电子自旋共振作为一种回顾性剂量测定技术在剂量重建中应用日益广泛。介绍了电子自旋共振剂量估算的基本原理和过程,包括样品的收集和准备、ESR的测量和信号处理、剂量校准、结果的解释、误差来源及新的进展。另外,还介绍了此技术在剂量重建中的一些应用实例。     

Radiation dose and risk from fluoroscopically guided percutaneous transluminal angioplasty and stenting in the abdominal region

The objective of this study was to estimate the radiation dose and associated risks resulting from fluoroscopically guided percutaneous transluminal angioplasty with or without stent placement in the abdominal region. Average examination parameters for renal and aortoiliac procedures were derived using data from 80 consecutive procedures performed in our institute. Organ and effective doses were estimated for endovascular procedures with the use of a Monte Carlo (MC) transport code and an adult mathematical phantom. Thermoluminescent dosimeters were used in an anthropomorphic phantom to verify MC calculations. Radiation-induced risks were estimated. Results are presented as doses normalized to dose area product, so that the patient dose from any technique and X-ray unit can be easily calculated for iliac and renal PTA/stenting sessions. The average effective dose varied from 75 to 371 μSv per Gycm² depending on the beam quality, procedure scheme and sex of the patient. Differences up to 17% were observed between MC-calculated data and data derived from thermoluminescent dosimetry. The radiation-induced cancer risk may be considerable for younger individuals undergoing transluminal angioplasty with stent placement.     

牙釉质电子顺磁共振剂量重建研究的若干进展

介绍了牙釉质电子顺磁共振回顾性剂量学的目前研究概况,着重阐述了低剂量区去除背景信号的新方法,同时也对其在体测量及紫外线影响等方面进行了讨论。     

嚼烟习俗地区的牙釉质电子自旋共振剂量学的研究

目的 研究嚼烟习俗对牙釉质电子自旋共振(ESR)剂量学的影响。方法 用机械方法获得20个孟买地区的舌侧牙釉质样品与10个混合均匀的日本人舌侧牙釉质样品。用⁶⁰Co γ射线分别照射部分牙釉质样品,使用ESR波谱仪测量辐射前和不同辐射剂量后牙釉质样品的ESR信号。结果 9个孟买牙釉质样品,其ESR的本底信号强度明显高于日本人的平均水平,为日本人水平的1.5~3.3倍。ESR本底信号强度较高的样品,γ射线照射后,剂量学信号的辐射响应略低,说明高本底可能降低了辐射剂量的灵敏度。6个样品辐射响应的平均值为(0.42±0.03)mGy,与日本牙釉质混合样品很相近。结论 嚼烟地区的部分牙釉质的ESR本底水平明显高于一般平均水平,可能是嚼烟中大量的烟碱与牙釉质相互作用的结果。进一步研究特殊生活习俗对牙釉质ESR剂量学的影响,有助于提高不同地区剂量重建的精度,为正确地评价辐射事故剂量提供科学依据。     

Radiation dosimetry in cell biology: comparison of calculated and measured absorbed dose for a range of culture vessels and clinical beam qualities

Purpose: Cell culture studies are frequently used to evaluate the effects of cancer treatments such as radiotherapy, hormone therapy, chemotherapy, nanoparticle enhancement, and to determine any synergies between the treatments. To achieve valid results, the absorbed dose of each therapy needs to be well known and controlled. In this study, we aim to determine the uncertainty associated with radiation exposure in different experimental conditions.

Materials and methods: We have performed an in-depth evaluation of the absorbed dose and dose distribution that would be delivered to a cell sample when cultivated in a number of the more popular designs of culture vessels. We focus on exposure to two beam types: a kilovoltage x-ray beam and a megavoltage photon beam, both of which are routinely used to treat cancer patients in the clinical environment.

Conclusions: Our results identify large variations of up to 16% in the absorbed dose across multi-well culture plates, which if ignored in radiobiological experiments, have the potential to lead to erroneous conclusions.     

Accuracy of the convolution/superposition dose calculation algorithm at the condition of electron disequilibrium

Using Monte Carlo simulation and the convolution/superposition algorithm, this work examines percent depth dose curves of the central axis in an acrylic phantom (20×20×20 cm³) with variously sized air cavities (20×20×1.0, 20×20×2.0, 20×20×3.0, 20×20×4.0 and 20×20×4.95 cm³ for study of longitudinal electron disequilibrium (ED) and 3.6×3.6×4.95, 4.5×4.5×4.95, 5.4×5.4×4.95 and 20×20×4.95 cm³ for study of lateral ED). Radiochromic film samples are also measured to verify the Monte Carlo results. The Monte Carlo simulation is performed using OMEGA/BEAM and DOSXYZ codes, and the convolution/superposition calculation relies on an ADAC commercial treatment planning system.

Underestimating the dose kernel expansion leads to overestimating the dose of what was found in the air cavity of ED using the convolution/superposition algorithm. Consequently, the dose in the rebuild-up region is influenced. The influenced region is on the acrylic phantom surface to a depth of about 0.5 cm. The density scaling method of the convolution/superposition algorithm, applied to heterogeneous media, should be enhanced to account for the over-expansion of the dose kernel in the cavity of ED.     

Overview of physical dosimetry methods for triage application integrated in the new European network RENEB

Abstract

Purpose: In the EC-funded project RENEB (Realizing the European Network in Biodosimetry), physical methods applied to fortuitous dosimetric materials are used to complement biological dosimetry, to increase dose assessment capacity for large-scale radiation/nuclear accidents. This paper describes the work performed to implement Optically Stimulated Luminescence (OSL) and Electron Paramagnetic Resonance (EPR) dosimetry techniques.

Materials and methods: OSL is applied to electronic components and EPR to touch-screen glass from mobile phones. To implement these new approaches, several blind tests and inter-laboratory comparisons (ILC) were organized for each assay.

Results: OSL systems have shown good performances. EPR systems also show good performance in controlled conditions, but ILC have also demonstrated that post-irradiation exposure to sunlight increases the complexity of the EPR signal analysis.

Conclusions: Physically-based dosimetry techniques present high capacity, new possibilities for accident dosimetry, especially in the case of large-scale events. Some of the techniques applied can be considered as operational (e.g. OSL on Surface Mounting Devices [SMD]) and provide a large increase of measurement capacity for existing networks. Other techniques and devices currently undergoing validation or development in Europe could lead to considerable increases in the capacity of the RENEB accident dosimetry network.     

质子加速器治疗室辐射防护优化研究

目的 研究铁屏蔽体在主防护墙中不同深度对防护墙外周围剂量当量率的影响。方法 采用FLUKA蒙特卡罗模拟程序构建了质子治疗室的模型,治疗室的屏蔽体由混凝土和钢构成。分别模拟220和250 MeV的质子照射水模体,以获得不同情况下的周围剂量当量率分布。结果 随着嵌入防护墙的铁屏蔽体深度的变化,两种模拟条件下质子治疗机房主防护墙外30 cm处的周围剂量当量率发生显著变化,最大周围剂量当量率（220 MeV：3.42 μSv/h,250 MeV：6.39 μSv/h）比最小周围剂量当量率（220 MeV：1.75 μSv/h,250 MeV：3.32 μSv/h）高2倍。结论 在质子治疗加速器的设计中,应仔细评估铁屏蔽体在主防护墙中的位置。     

Feasibility study of SPECT system for online dosimetry imaging in boron neutron capture therapy

A single collimator version of a proposed PG-SPECT system was manufactured and experimentally tested. Combining this experimental data with Monte Carlo simulation, the viability of Ge and CdTe semiconductors detectors was calculated. It was determined that the best detector of the ones compared would be a CdTe detector of 2–3 mm, aided by the benefit of adding a Compton-suppression anti-coincidence timing detector.     

Effects of heterogeneities in dose distributions under nonreference conditions: Monte Carlo simulation vs dose calculation algorithms

The purpose of this study is to evaluate the performance of dose calculation algorithms used in radiotherapy treatment planning systems (TPSs) in comparison with Monte Carlo (MC) simulations in nonelectronic equilibrium conditions. MC simulations with PENELOPE package were performed for comparison of doses calculated by pencil beam convolution (PBC), analytical anisotropy algorithm (AAA), and Acuros XB TPS algorithms. Relative depth dose curves were calculated in heterogeneous water phantoms with layers of bone (1.8?g/cm³) and lung (0.3?g/cm³) equivalent materials for radiation fields between 1?×?1?cm² and 10?×?10?cm². Analysis of relative depth dose curves at the water-bone interface shows that PBC and AAA algorithms present the largest differences to MC calculations (u_MC?=?0.5%), with maximum differences of up to 4.3% of maximum dose. For the lung-equivalent material and 1?×?1?cm² field, differences can be up to 24.3% for PBC, 11.5% for AAA, and 7.5% for Acuros. Results show that Acurus presents the best agreement with MC simulation data with equivalent accuracy for modeling radiotherapy dose deposition especially in regions where electronic equilibrium does not hold. For typical (nonsmall) fields used in radiotherapy, AAA and PBC can exhibit reasonable agreement with MC results even in regions of heterogeneities.     

一起介入手术过量照射事件中术者关键组织器官吸收剂量和有效剂量的蒙特卡罗估算

目的 使用蒙特卡罗方法对一起介入手术过量照射事件中两名术者的组织器官剂量和有效剂量进行估算。方法 基于国际放射防护委员会(ICRP)145号报告的成人网格型参考计算体模(MRCPs)和体模变形技术构建术者模型和前期工作中构建的患者模型,根据现场设备和照射条件构建实际照射场景模型,使用蒙特卡罗模拟方法评估术者眼晶状体、甲状腺等关键组织和器官的吸收剂量和全身有效剂量。结果 在本次事件特定曝光条件下,两名术者主要器官的最大吸收剂量均产生在左眼晶状体,分别为1.216和0.223 mGy,甲状腺吸收剂量分别为0.074和0.019 mGy,两术者有效剂量分别为0.088和0.021 mSv。穿戴铅衣和铅围脖时两术者有效剂量降低率分别为67.16%和78.79%。结论 结合蒙特卡罗方法和人体曲面模型可较高程度还原某一特定照射场景,用于估算受照人员的物理剂量。     

An in silico study on the effect of host tissue at brachytherapy dose enhancement by gold nanoparticles

PurposeIridium-192 brachytherapy dose enhancement by gold nanoparticles was investigated in five different tumor tissues to observe the tissue-related differences as an effective environmental factor in the applications of nanoparticles as radio-enhancer agents.Methods and MaterialsThe brachytherapy high-dose-rate source of BEBIG Ir-192, a tumor volume with five different tissues including water, Plexiglas, soft tissue, adipose, and bone with and without a uniform distribution of gold nanoparticles were mimicked by MCNPX Monte Carlo simulation code using lattice feature. Dose enhancement factors in the tumor volume were measured separately regarding the types of tissue, and a previous study using GEometry ANd Tracking 4 simulation was used for result validation.ResultsThe results demonstrated that various types of tissue, as the host of gold nanoparticles, lead to different dose enhancement level, so that the bone and adipose have the lowest and the highest amount of dose enhancement factor with values 20.8% and 39.75%, respectively. The maximum difference of 4.8% was achieved from data benchmarking.ConclusionsThe results of this study indicate that the MCNPX code can be used as a valid tool for dose measurement in the presence of nanoparticles. Moreover, tissue types of tumor as an environmental feature, alongside with the nanoparticle's size and concentration as well as the conditions of radiotherapy, should be considered in the dose calculation.     

Monte carlo dose calculations in the treatment of a pelvis with implant and comparison with pencil-beam calculations

In the present paper, dose distribution calculated with the Monte Carlo code EGS4 and with a pencil-beam algorithm are compared for the treatment of a pelvis with an implant. Overestimations of dose values inside the target volume by the pencil-beam algorithm of up to 10% were found, which are attributed to the underestimation of the absorption of photons by the implant. The differences in dose distributions are also expressed by comparing the tumor control probability (TCP) of the Monte Carlo dose calculations with the TCP of the pencil-beam calculations. A TCP reduction of order of 30% was found.     

Simulations of thermal tissue coagulation and their value for the planning and monitoring of laser-induced interstitial thermotherapy (LITT).

MRI information is widely used for the monitoring of thermal therapies, such as laser-induced interstitial thermotherapy (LITT). However, a detailed knowledge about the relationship between time/temperature exposure and resulting tissue thermal damage is needed to estimate the lesion extent. The aims of this work were to model the thermal response of laser-irradiated tissue and to assess the value of Monte Carlo simulation (MCS) for tumor therapy planning and monitoring. MCS yielded true 3D distributions of laser-induced temperature and thermal damage. These results were compared with 2D MR thermometry data from in vitro experiments performed on animal liver tissue over an ordinary range of laser powers (10-25 W) and irradiation times (5-25 min). Clinical reference data were available from MR-guided liver LITT procedures. MCS correctly predicted the shape of temperature and damage distributions. The quantitative agreement between simulated and measured lesion diameters was within 10% and 15% for the in vitro and in vivo cases, respectively. The simulated 53 degrees C isotherm best estimated the boundary of the final thermal damage (6% variance). This study shows that MCS of interstitial laser coagulation provides unique information that can be of use in the empirical correlation of temperature with thermal damage, and can assist greatly in thermal treatment planning and monitoring.