用MCNP4b研究32P液体球囊吸收剂量分布

32P的液体β源球囊是治疗冠状动脉粥样硬化疾病的一种新方法,笔者曾报道32P液体球囊用Loevinger剂量点核解析函数计算的一维径向吸收剂量分布[1].本研究用模拟实验测量,改进的剂量点核函数和4b版蒙特卡罗输运代码(MCNP4b)3种方法估算32P液体球囊在血管模拟体内的吸收剂量.     

放射性球囊内气泡对血管组织剂量分布的影响

目的：计算放射性球囊治疗冠状动脉再狭窄时球囊内气泡对血管的剂量分布影响。方法：采用Prestwich的剂量点核函数计算球囊周围的剂量分布，计算体积为0.02mL的气泡位于球囊壁中心和边缘两种情况下对球囊周围组织的剂量分布影响，并与无气泡的液体球囊比较。结果：气泡在球囊壁中心时，影响范围为4mm,球囊两侧的剂量不均匀最大可达38％；在边缘时，影响范围为6mm，剂量不均匀达47％。结论：球囊内气泡对血管组织的剂量分布有影响。     

β源支架剂量分布的蒙特卡罗算法

目的 比较数值积分和蒙特卡罗方法计算的放射性支架的剂量率分布。方法 以3种有代表性的剂量点核函数为计算模型，计算支架的剂量率分布。结果 分别计算了中心面的径向，支架表面及离支架表面0.5mm处的轴向剂量分布，径向最大差异为1．5％，轴向的差异也有1．5％之内。结论 3种函数用数值积分和蒙特卡罗方法计算的剂量分布是一致的，蒙特卡罗方法可用来计算放射性支架的剂量分布。     

用能量沉积核函数方法计算~(60)Co照射野的吸收剂量

目的　介绍了用能量沉积核函数方法计算60 Co照射野吸收剂量的方法。方法　能量沉积核函数方法将吸收剂量的贡献分为 3部分 :原射线、单次散射和多次散射。它使用基本的剂量学数据 ,如射野中心轴百分深度剂量、离轴比和准直系统散射输出因子等 ,这些数据在Fyc 5 0H治疗机上用方形照射野测量得到。再用能量沉积核函数计算吸收剂量。并讨论了散射线对吸收剂量的影响。结果　从测量数据得到了原射线和散射线的能量沉积核函数 ,并利用能量沉积核函数计算60 Co照射野的主要剂量学参数 ,计算值和测量值是一致的 ;不规则照射野的吸收剂量及其分布的计算结果也和测量结果符合得很好。结论　能量沉积核函数方法适用于较精确地计算60 Co不规则照射野的吸收剂量。     

用能量沉积核函数方法计算60Co照射野的吸收剂量

目的 介绍了用能量沉积核函数方法计算＾６０Ｃｏ照射野吸收剂理的方法。方法 能量沉积核函数方法将吸收剂量的贡献分为３部分：原射线、单次散射和多次散射。它使用基本的剂量学数据,如射野中心轴百分深度剂量、离轴比和淮直系统散射输出因子等,这些数据在Ｆｙｃ５０Ｈ治疗机上用方形照射野测量得到,再用能量沉积核函数计算吸收剂量,并讨论了散射线对吸收剂量的影响。结果 从测量数据得到了原射线和散射线的能量沉积核函数,并利用能量沉积核函数计算＾６０Ｃｏ照射野的主要剂量学参数。计算值和测量值是一致的;不规则照射野的吸收剂量及其分布的计算结果也和测量结果符合得很好。结论 能量沉积核函数方法适用于较精确地计算＾６０Ｃｏ不规则照射野的吸收剂量。     

冠心病影像学检查与辐射剂量

核心脏病学技术、心脏CT扫描和冠状动脉造影等是最常用的冠心病影像诊断技术,在降低冠心病的发病率和病死率方面具有重要的地位。随着这些技术的快速发展,辐射问题也越来越被专业人员和社会大众所关注,通过准确评价辐射剂量以及有效减少辐射剂量使冠心病的各种影像学技术得以更广泛、更合理的临床应用。     

基于胸围的管电流调制技术在冠状动脉CT造影应用的可行性探讨

目的：建立以胸围为参考指标调节冠状动脉CT造影（CTA）成像管电流的函数模型,并探讨其个体化管电流调节模型的临床应用的可行性。方法：连续选取68例以自动管电流调节模式扫描的胸部CT病例,建立胸围与管电流之间的函数模型;再应用其建立的胸围-管电流函数模型对另外的连续64例病例进行冠状动脉CTA成像,对图像质量进行评分,并记录噪声值、管电流、辐射剂量等指标。结果：胸围与管电流之间的函数模型以POW函数拟合度最好（R²=0.691,P<0.05）。应用胸围-管电流函数模型冠状动脉CTA成像的平均图像等级评分为（3.38±0.72）分,噪声值为（31.02±3.97）HU,管电流为（390.63±89.30）mA,CTDI_vol为（34.83±10.72）mGy,DLP为（751.67±175.16）mGy·cm。 结论：以胸围为参考指标调节冠状动脉CTA成像管电流方法,能够较好地实现个体化辐射剂量控制,临床应用具有可行性。     

介入诊疗对心血管病患者外周淋巴细胞DNA的损伤

目的探讨心血管病介入诊疗中的X线电离辐射对心血管病患者DNA损伤的影响。方法收治接受心血管病介入诊疗患者244例,按介入术式不同分为四组:经皮冠状动脉造影术组87例,经皮冠状动脉介入术组72例,射频消融术组48例,起搏器植入术组37例。分别于术前、术后2 h、24 h抽取患者外周血,检测外周血淋巴细胞染色体微核。同时记录患者手术全程辐射的累积皮肤表面入射剂量(CD)、面积剂量乘积(DAP)、透视时间(FT)等,观察各种介入诊疗中患者接受的辐射损伤程度和差异。结果经皮冠状动脉支架置入术组CD和DAP值显著高于其他三组,而其他三组间CD和DAP值差异无统计学意义(P>0.05)。患者术后2 h染色体微核率为16.3‰±4.2‰,P<0.05),术后24 h为17.5‰±5.1‰,,明显高于术前水平(13.8‰±4.7‰,P<0.05)。结论不同介入术中,患者接受的辐射剂量不同,但介入诊疗中的电离辐射都可能会造成患者的DNA损伤。     

一种计算不规则野的散射剂量的方法研究

目的寻找一种可用于计算放射治疗不规则野的散射剂量的可靠方法。方法通过对原用于计算规则野等效方野的Day氏函数法进行改进,使之扩大应用到不规则野,从而既能计算不规则野的等效方野,也可以计算不规则野中任意点的散射剂量。结果改进后的Day氏函数随照射深度的变化进行修正,大大提高了计算精度,不规则野的散射剂量的计算误差在1.5%以内。结论用改进的Day氏函数法可以计算不同照射能量和照射深度的任意形状射野的散射剂量,并取得满意的精度。     

320排CT冠状动脉成像对右冠状动脉起源变异的诊断价值

目的 探讨320排CT冠状动脉成像对于右冠状动脉起源变异的诊断价值.方法 回顾性分析行320排CT、64层CT冠状动脉成像检出右冠状动脉起源变异19例的临床资料,评价两组冠状动脉变异的检出情况及图像质量、辐射剂量等差异.结果 右冠状动脉起源于左冠状窦或窦上嵴为较常见的具有潜在危险的冠状动脉变异类型;CT冠状动脉成像多平面重组(MPR)、薄层最大密度投影(MIP)重组可较直观地显示右冠状动脉起源变异;320排CT冠状动脉成像在保证图像质量的基础上,能有效降低辐射剂量(P=0.000).结论 320排CT冠状动脉成像无创、准确、辐射剂量较低,可作为冠状动脉变异的筛查手段,对于冠心病的预防及治疗具有一定的临床意义.     

Internal radionuclide radiation dosimetry: a review of basic concepts and recent developments.

Internal dosimetry deals with the determination of the amount and the spatial and temporal distribution of radiation energy deposited in tissue by radionuclides within the body. Nuclear medicine has been largely a diagnostic specialty, and model-derived average organ dose estimates for risk assessment, the traditional application of the MIRD schema, have proven entirely adequate. However, to the extent that specific patients deviate kinetically and anatomically from the model used, such dose estimates will be inaccurate. With the increasing therapeutic application of internal radionuclides and the need for greater accuracy, radiation dosimetry in nuclear medicine is evolving from population- and organ-average to patient- and position-specific dose estimation. Beginning with the relevant quantities and units, this article reviews the historical methods and newly developed concepts and techniques to characterize radionuclide radiation doses. The latter include the 3 principal approaches to the calculation of macroscopic nonuniform dose distributions: dose point-kernel convolution, Monte Carlo simulation, and voxel S factors. Radiation dosimetry in "sensitive" populations, including pregnant women, nursing mothers, and children, also will be reviewed.     

Effects of Anaesthetic Agent on [31P]NMR High-energy Phosphates and Regional Distributions of Intravascular Oxyhaemoglobin Saturations

Abstract

Purpose: The biological response of tissue exposed to radiations emitted by internal radioactivity is often correlated with the mean absorbed dose to a tissue element. However, experimental studies show that even when the mean absorbed dose to the tissue element is constant, the response of the cell population within the tissue element can vary significantly depending on the distribution of radioactivity at the cellular and multicellular levels. The present work develops theoretical models to simulate these observations.

Materials and methods: Two theoretical models were created to simulate experimental three-dimensional cell culture models with homogeneous and inhomogeneous tissue environments. The cells were assigned activities according to lognormal distributions of an alpha particle emitter or a monoenergetic electron emitter. Absorbed doses to the cell nuclei were assessed with point-kernel geometric-factor and Electron Gamma Shower version nrc (EGSnrc) Monte Carlo radiation transport simulations, respectively. The self- and cross-dose to individual cell nuclei were calculated and a Monte Carlo method was used to determine their fate. Survival curves were produced after tallying the live and dead cells.

Results: Both percent cells labeled and breadth of lognormal distribution affected the dose distribution at the cellular level, which in turn, influenced the shape of the cell survival curves.

Conclusions: Multicellular Monte Carlo dosimetry-models offer improved capacity to predict response to radiopharmaceuticals compared to approaches based on mean absorbed dose to the tissue.     

Liposome-mediated radiotherapeutics within avascular tumor spheroids: comparative dosimetry study for various radionuclides, liposome systems, and a targeting antibody.

Absorbed dose profiles within tumor spheroids simulating avascular micrometastases have been calculated for a variety of liposome- and antibody-radionuclide combinations to assess the anticipated therapeutic efficacy based on the intratumoral distribution of the carrier systems within the spheroid model. METHODS: Experiments studying the targeting and diffusion capability of the most clinically relevant liposome systems and the anti-PSMA (prostate-specific membrane antigen) antibody J591 within spheroids of the prostate cancer cell line LNCaP (diameter, 150-200 mum) have been performed. The intratumoral biodistribution data were then used as the input to obtain absorbed dose profiles within the tumor spheroid mass. The dosimetric analysis was performed for a variety of medium- and high-energy beta-emitting radionuclides ((32)P, (90)Y, (188)Re, (67)Cu, (131)I) and 2 low-energy Auger or conversion electron emitters ((123)I, (125)I) following the point-kernel convolution method in the continuous slowing-down approximation. RESULTS: Relative absorbed dose distribution calculations as a function of the distance from the rim of the spheroids are presented. For all liposome systems studied, the SUV-DMPC-chol (small unilamellar vesicle-dimyristoyl-phosphatidylcholine-cholesterol) was most efficient in penetrating deeper within the spheroids. For the beta-emitters it delivered its maximum absorbed dose (D(max)) at 40- to 50-microm depth, exhibiting an almost flat absorbed dose profile beyond that point, as is evident by the high absorbed dose value at the center of the spheroid (D(core)), D(core)/D(max) > 0.9; the respective values for the J591 antibody were 20 mum and 0.85. The Auger or conversion emitters resulted in the most heterogeneous absorbed dose distribution; the ratio D(core)/D(max) fell to 0.4 for the SUV-DMPC-chol and to 0.4-0.5 for the antibody. In general, a 2- to 10-fold "cross-fire"-related increase of the core absorbed dose was observed. For liposomes exhibiting high binding capacity (3beta-[N-(N',N']-dimethylaminoethane)carbamoyl]cholesterol [DC-chol]), however, the low-energy emitters deliver up to a 40% higher D(max) relative to the beta-emitters. The surface characteristics of liposomes appear to have a noticeable influence on the absorbed dose profiles. The use of neutral (DMPC-chol) versus cationic (DC-chol) lipids resulted in up to a 10-fold increase of D(core)/D(max) depending on the radionuclide. Changing the cationic lipid used to N-[1-(2,3-dioleoyloxy)propyl]-N,N,N-trimethylammonium methyl sulfate also had a notable influence (up to a 6-fold increase), whereas the effect of fusogenic lipids (dioleoylphosphatidylcholine) was found to be much smaller. CONCLUSION: It is possible to engineer liposome systems that are particularly effective in delivering an almost uniform absorbed dose profile at the central region of micrometastatic tumors, provided that conjugates with the appropriate radionuclides are constructed. In view of the passive means of diffusion of liposomes within solid tumors, it is suggested that they may effectively complement an antibody-based therapeutic regime against micrometastatic tumors, leading to cytotoxic absorbed dose levels throughout the entire tumor volume--thus, hindering tumor recurrence.     

Dosimetry from organ to cellular dimensions.

While the conventional Medical Internal Radiation Dose (MIRD) approach is useful for estimating approximate organ absorbed doses in diagnostic applications of isotopes, this strategy is suited neither to the exacting requirements of targeted radionuclide therapy nor to radiopharmaceuticals with a non-uniform activity distribution. For the individual treatment planning of patients treated with common radionuclides emitting high energy betas, the individual activity distribution has to be obtained from CT-SPECT images and the doses to the target organs and critical tissues have to be calculated by point-kernel methods. Due to the stochastic nature, alpha-radioimmunotherapy (alpha-RIT) requires microdosimetric calculations with Monte Carlo on a realistic model of the source and target tissue at the micrometer level. For a prediction of the biological effects of intracellular labelling with Auger electron emitters an accurate subcellular modelling including the DNA structure at the nanometre level with knowledge of the target for the considered biological effect is necessary.     

Murine S factors for liver, spleen, and kidney.

Preclinical evaluation of new radiopharmaceuticals is performed in animal systems before testing is started in humans. These studies, often performed in murine or other rodent models, are important in understanding the relationship between absorbed dose and response, which can be translated to preclinical results for humans. In performing such calculations, either electrons are assumed to deposit all of their energy locally or idealized models of mouse anatomy are used to determine absorbed fractions. Photon contributions are generally considered negligible. To improve the accuracy of such absorbed dose calculations, mouse-specific S factors for (131)I, (153)Sm, (32)P, (188)Re, and (90)Y have been generated, and the photon and electron portions have been tabulated separately. Absorbed fractions for 5 monoenergetic electrons, ranging in energy from 0.5 to 2 MeV, are also provided. METHODS: Female athymic mouse MR images were obtained on a 4.7-T MRI device. Fifteen T1-weighted, 1.5-mm-thick slices (0.5-mm gap) were collected. Using a previously developed software package, 3-dimensional Internal Dosimetry (3D-ID), organ contours were drawn to obtain a 3-dimensional representation of liver, kidneys, and spleen. Using a point-kernel convolution, the mean absorbed dose to each organ from the individual contributions of each source organ were calculated. S factor equivalent values were obtained by assuming a uniform distribution of radioactivity in each organ. Results were validated by comparing 3D-ID generated electron S factors for different-sized spheres with published data. Depending on matrix size, sphere size, and radionuclide, 1% (256(2) matrix) to 18% (64(2) matrix) agreement was obtained. RESULTS: S factor values were calculated for liver, spleen, and right and left kidneys. Cross-organ electron-absorbed fractions of up to 0.33 were obtained (e.g., (90)Y right kidney to liver). Comparisons between S factor values and values obtained assuming complete absorption of electron energy yielded differences of more than 190% ((90)Y spleen self-dose). CONCLUSION: The effect of cross-organ and self-absorbed dose is dependent on emission energy and organ geometry and should be considered in murine dose estimates. The approach used to generate these S factors is applicable to other animal systems and also to nonuniform activity distributions that may be obtained by small-animal SPECT or PET imaging or by quantitative autoradiography.     

Elements of commissioning step-and-shoot IMRT: Delivery equipment and planning system issues posed by small segment dimensions and small monitor units

The implementation of intensity-modulated radiation therapy (IMRT) in the clinic necessitates commissioning for all systems involved. This paper describes work carried out for the treatment planning system (Helax-TMS version 6.1) and the treatment delivery equipment (Siemens Primus) available at our center. Particular regard was paid to small monitor units (MUs) and small field segments typical of step-and-shoot IMRT plans. The beam profile stability of the Siemens Primus accelerators when delivering small MU was examined with a linear detector array. Dose monitor linearity and intersegment variations were measured with a 0.6-cm³ ionization chamber. Treatment planning system calculated total scatter factors (S_cp) and beam profiles for symmetric and asymmetric small fields for 6- and 15MV beams were compared against measurements in water using a 0.125-cm³ ionization chamber and a diamond detector. The 6- and 15MV beams from the Primus accelerators were found to be stable at MUs less than 10. Dose monitor linearity for small exposures under 10 MU was within ± 2% for 6 MV, but found to be not so initially for 15 MV. This could be remedied by an adjustment of a soft spot on the Siemens Primus. The delivery of small MU segments as part of an IMRT sequence was found to be consistent down to segment sizes of 1 MU. The treatment planning system pencil-beam convolution model agreed with measurement within ± 5% for fields collimated down to 3 × 3 cm. The collapsed cone point-kernel model better predicted the output for the smallest field, but displayed some unpredictable shifts in the position of the penumbra. The startup characteristics of Siemens Primus accelerators were found suitable for step-and-shoot IMRT. The diminution in accuracy of Helax-TMS dose calculation models for multileaf collimated fields of less than 2 × 2 cm has led us to avoid these in IMRT treatments at our center.     

Elements of commissioning step-and-shoot IMRT: Delivery equipment and planning system issues posed by small segment dimensions and small monitor units

The implementation of intensity-modulated radiation therapy (IMRT) in the clinic necessitates commissioning for all systems involved. This paper describes work carried out for the treatment planning system (Helax-TMS version 6.1) and the treatment delivery equipment (Siemens Primus) available at our center. Particular regard was paid to small monitor units (MUs) and small field segments typical of step-and-shoot IMRT plans. The beam profile stability of the Siemens Primus accelerators when delivering small MU was examined with a linear detector array. Dose monitor linearity and intersegment variations were measured with a 0.6-cm³ ionization chamber. Treatment planning system calculated total scatter factors (S_cp) and beam profiles for symmetric and asymmetric small fields for 6- and 15MV beams were compared against measurements in water using a 0.125-cm³ ionization chamber and a diamond detector. The 6- and 15MV beams from the Primus accelerators were found to be stable at MUs less than 10. Dose monitor linearity for small exposures under 10 MU was within ± 2% for 6 MV, but found to be not so initially for 15 MV. This could be remedied by an adjustment of a soft spot on the Siemens Primus. The delivery of small MU segments as part of an IMRT sequence was found to be consistent down to segment sizes of 1 MU. The treatment planning system pencil-beam convolution model agreed with measurement within ± 5% for fields collimated down to 3 × 3 cm. The collapsed cone point-kernel model better predicted the output for the smallest field, but displayed some unpredictable shifts in the position of the penumbra. The startup characteristics of Siemens Primus accelerators were found suitable for step-and-shoot IMRT. The diminution in accuracy of Helax-TMS dose calculation models for multileaf collimated fields of less than 2 × 2 cm has led us to avoid these in IMRT treatments at our center.     

Water-energy dosage calibration and standard ion dosage calibration--a comparison in ultrahard x-ray radiation

Ten ionization chambers (PTW), partly of different type, which all have been calibrated in terms of absorbed dose to water, were used to compare the absorbed dose indicated in a reference geometry at 8 MV X-rays. The standard deviation of the mean value of the absorbed dose determined for all chambers was 0.5%. Since 4 chambers have been calibrated in terms of absorbed dose to water and in exposure, the absorbed dose to water was determined from indicated value according to both calibration procedures. The dose values obtained via the energy dose calibration turned out to be about 2.5% less compared to the result when applying the exposure calibration factor.     

Dosimetry of cathetron applicators in intracavitary therapy

Theoretical computations have been done to obtain dose distributions in the paracervical and sagittal planes for various loadings of Cathetron applicators. Uterine catheters of various sizes and shapes and various loadings of ovoid catheters have been considered for the dosimetry. Experimental measurements have been made to verify the computed dose distributions. The computed dose distributions have also been compared with those of a conventional Manchester loading. Although the ratio of dose contribution to point A from vaginal sources to that from the uterine sources is found to be significantly different for Cathetron therapy from the conventional Manchester system, the isodose distributions in the paracervical plane are in good agreement. However, the differences in the isodose distributions in the sagittal plane indicates a higher dose to the rectal region for Cathetron therapy, which can be reduced by the use of rectal retractors.     

Organ doses, detriment and genetic risk from interventional vascular procedures in Málaga (Spain)

Nowadays, the radiological risk from simple X-ray procedures is well known. The purpose of this work has been to estimate the population risk from digital angiographic and interventional procedures and to compare it with the one from simple procedures in the same population. The population risk has been estimated according to the following quantities: genetically significant dose, somatic significant dose, collective effective dose, annual per caput effective dose and detriment. These have been estimated from dose area product and organ dose. Organ dose values were estimated with the Eff-Dose software. A population of 605410 people were included in the study. In 1996, 1312 patients were to digital interventional vascular procedures in Malaga, and 159 of them were selected in this research project to obtain the dose area product and organ dose. The results obtained for the quantities evaluated are: genetically significant dose, 4.1 microGy; somatic significant dose, 0.9 mSv; collective effective dose, 11.65 person-Sv: annual per caput effective dose, 0.02 mSv and detriment, 0.65 radiogenic cancers per year. These procedures supply a high radiation dose, so they should have a greater contribution to population dose and risk than simple examinations. However, our results indicate just the opposite.