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。     

术中放疗的吸收剂量测算方法的研究

目的 研究和比较水、固体水及有机玻璃3种模体的术中放疗吸收剂量的测算方法。方法 对于3种模体,使用固定在水模体中的电离室对加速器的电子速术中放疗限光筒进行吸收剂量的测算,首先选定参考限光筒对所有能量的电子束在源皮距SSD=100cm,水模内射束中心轴上特定深度,通过调整加速器使1cGy=1MU,然后使用术中放疗及参考限光筒在相同的辐照条件下进行测量,即测量术中放疗限光筒的输出因数,对于水模体,计算出各限光筒的吸收剂量cGy对应的加速器输出MU数值,并据此计算出固体水模体和有机玻璃模体的各限光筒吸收剂量cGy对应的加速器输出的MU数值,结果 相对于水模体,有机玻璃模体的测量误差为0.27%,固体水为0.45%。结论 对没有专用测量水箱和固体水的医院使用有机玻璃模体进行吸收剂量的测量不失为一种切实可行的方法。     

电子束吸收剂量的测量

国际原子能机构 (IAEA) 2 77号技术报告 (TRSNo 2 77)关于光子与电子束吸收剂量测量的国际实用规程规定对于医用加速器高能电子束吸收剂量校准的参考深度 ,当水模表面的平均能量 E0 MeV <5时 ,选在模体中的最大剂量深度(R1 0 0 ) ;而 5≤ E0 MeV <10、10≤ E0 MeV <2 0、2 0≤ E0 MeV时 ,分别选在水下 1,2 ,3cm或最大剂量深度[1 ,2 ] ,并且对于电子束在模体表面的平均能量 E0 =10MeV以下 ,建议使用平行板电离室对吸收剂量进行测量 ;低于 5MeV必须使用平行板电离室 ;而在 E0 =10MeV以上 ,平行板电离室也非常适于吸收剂量…     

猪白细胞在体内或体外经裂变中子照射后的染色体畸变

本文报导了猪白细胞在体内和体外用不同水平的裂变中子照射后的染色体畸变。所用反应堆裂变中子的平均能量为1.2百万电子伏,γ射线的平均能量为2百万电子伏,中子与γ射线的比值为6:1。以平均组织剂量估算白细胞的受照剂量,平均组织剂量系根据组织当量模型在不同深度内的测量结果求得。每组两头母猪,剂量率为14.3拉德/分,总剂量     

俄歇电子发射核素靶向治疗中细胞平均吸收剂量的计算

目的 给出一种新的方法,计算俄歇电子发射核素在细胞中均匀分布和非均匀分布时细胞和细胞核的平均吸收剂量以吸引剂量在细胞内的分布。方法 俄歇电子单位路径的能量损失用多项式拟合,用解析方法给出点源在细胞或细胞核内的能量沉积,从而得到不同源－靶组合的S值。放射性核素在细胞中径向线性分布和指数分布,分别计算了细胞和细胞核的平均吸收剂量;以及放射源距细胞中心不同距离时对细胞吸收剂量的影响。光子对细胞或细胞核的剂量贡献忽略不计。结果 平均吸收剂量及其在细胞内的分布和细胞的大小、俄歇电子能谱、核素的空间分布密切相关。细胞核内的核素对细胞核吸收剂量的贡献远大于细胞质中的核素。结论 俄歇电子在生物组织中的射程短,单位路径的能量损失高,能产生非常高的局部能量沉积。我们给出的细胞平均吸收剂量的解析计算方法计算速度快,结果可靠。     

贴壁细胞β射线内照射吸收剂量的计算

目的：寻求贴壁细胞β射线内照射吸收剂量的计算公式。方法：根据辐射吸收剂量定义和MIRD方案进行推导。从悬浮细胞培养模式入手,考虑到贴壁细胞培养的特殊性,以及其受照射的方向,依据累积放射性活度、β射线能量、培养液质量计算辐吸收剂量。结果：得到悬浮细胞、贴壁细胞β射线内照射吸收剂量的计算公式。并进行计算验证。结论：该公式使用简便,可靠性强,准确性好,便于实际应用。     

CT扫描所致受检者器官剂量的体模实验研究

目的 了解不同部位X射线CT扫描所致受检者器官或组织的吸收剂量及其分布。方法 实测体模中重要组织器官的CT值,并转换成线性吸收系数与人体正常值进行比较;在体模中 布放光致辐射发光玻璃剂量计,分别模拟测量头部、胸部、腹部和盆腔CT扫描所致受检者主要器官或组织的吸收剂量。结果 实验用仿真人体模具有良好的组织等效性。头部扫描吸收剂量最大的器官是大脑,胸部扫描吸收剂量较大的器官是甲状腺、乳腺、肺和食道,腹部扫描吸收剂量较大的器官是肝、胃、结肠和肺,单次盆腔扫描体所致骨表面和结肠的吸收剂量可达50 mGy以上。结论 X射线CT扫描所致受检者的器官剂量及其分布随扫描部位的不同而异。盆腔扫描时结肠、红骨髓、性腺和膀胱等主要器官的吸收剂量较大,应引起注意。     

β核素球囊预防血管再狭窄的临床剂量估算

目的 探讨核素球囊内照射血管内的吸收剂量分布规律。方法 ①依据吸收剂量点核函数模拟计算^90Y、^186Re、^32P灌注球囊时血管组织中的吸收剂量率分布；②用非线性最小二乘法对吸收剂量率随球囊外径及组织深度的变化进行曲线拟合，并由此导出便于临床使用的经验公式。结果 球囊中吸收剂量率峰值出现在血管腔内球囊中，血管表面位于吸收剂量率曲线的拐点处，血管壁及周围组织中的吸收剂量率以近双指数方式下降。吸收剂量、持续照射时间、初始放射性浓度、组织深度及球囊外半径间的关系可用一经验公式表达。结论 血管组织中的β核素吸收剂量分布呈快速下降。该经验公式具有实用价值。     

热释光剂量计测量125I粒子源植入中职业人员剂量方法研究

目的 研究用热释光剂量计(TLD)测量并计算¹²⁵I粒子源植入中职业人员器官和组织接受的吸收剂量及有效剂量方法。方法 用⁶⁰Co γ射线开展TLD稳定性等相关性能实验。用¹²⁵I粒子源照射一组TLD片,建立空气比释动能标准剂量曲线。将TLD片分别贴在粒子源植入过程中职业人员铅衣内外甲状腺等13个部位,测量平均吸收剂量,计算器官和组织的吸收剂量和有效剂量。结果 3例前列腺癌粒子源植入术中,职业人员铅衣外器官和组织吸收剂量0.02~3.80 μGy,有效剂量0.06~1.81 μSv;铅衣内最高吸收剂量2.35 μGy,有效剂量0.02 μSv,屏蔽65.9%以上γ射线。3例脑癌中,职业人员铅衣外器官和组织吸收剂量0.23~11.31 μGy,有效剂量0.88~4.07 μSv;铅衣内最高吸收剂量2.22 μGy,有效剂量0.09 μSv,屏蔽54.5%以上射线。3例肺癌中,职业人员铅衣外器官和组织吸收剂量0.03~14.78 μGy,有效剂量0.35~7.59 μSv;铅衣内最高吸收剂量4.09 μGy,有效剂量0.22 μSv,屏蔽58.4%以上射线。2例纵隔癌中,职业人员铅衣外器官和组织的吸收剂量为0.06~74.91 μGy,有效剂量0.83~17.96 μSv;铅衣内最高吸收剂量10.29 μGy,有效剂量0.50 μSv,屏蔽85%以上射线。1例卵巢癌中,职业人员铅衣外器官和组织吸收剂量0.09~14.29 μGy,有效剂量2.40~4.50 μSv;铅衣内最高吸收剂量7.77 μGy,有效剂量0.12 μSv,屏蔽33.4%以上射线。植入1例眼睛癌中,职业人员铅衣外器官和组织吸收剂量为2.20~39.84 μGy,有效剂量4.48~10.06 μSv;铅衣内最高吸收剂量5.19 μGy,有效剂量0.16 μSv,屏蔽54.6%以上射线。结论 用TLD监测粒子源植入中职业人员剂量的方法简单易行,是保护近距离植入粒子源治疗中医务人员健康的有效措施。     

Evaluation of absorbed dose in respiratory-gated radiotherapy using a phantom system that simulates patient respiration

Respiratory-gated (RG) radiotherapy is useful for minimizing the irradiated volume of normal tissues resulting from the shifting of internal structures caused by respiratory movement. In this technique, although improvement in the dose distribution of the target can be expected, the actual absorbed dose distribution is not clearly determined. Therefore, it is important to clarify the absorbed dose at the tumor and at the evaluation points according to the patient's respiration. We have developed a phantom system that simulates patient respiration (TNK Co., Ltd.), to evaluate the absorbed dose and ensure precise RG radiotherapy. Actual patient respiratory signals were obtained using a respiratory synchronization and gating system (AZ-733V, Anzai Medical). The acquired data were then transferred to a phantom system driven by a ball screw to simulate the shifting of internal structures caused by respiratory movement. We measured the absorbed dose using a micro-ionization chamber dosimeter and the dose distribution using the film method for RG irradiation at expiratory phase by using Linac (PRIMUS, Toshiba Medical Systems Corp.) X-rays. When the distance of phantom movement was set to the average patient respiratory movement distance of 1.5 cm, we first compared absorbed dose with RG irradiation with a gating signal of 50% or less, and without RG irradiation. The absorbed dose at the iso-center was improved by 6.0% and 4.4% at a field size of 4x4 cm2, and by 1.3% and 0.7% at a field size of 5x5 cm2 with an X-ray energy of 6 MV and 10 MV, respectively. There was, however, no dose change at a field size of 10x10 cm2 and 15x15 cm2. When the gating signal was reduced to 25% and 10%, absorbed dose was also improved. With regard to the flatness of the dose profile, no changes in dose distribution were observed in the lateral direction, e.g., beam flatness was within 1.4% and 1.6% at field sizes of 5x5 cm2 and 10x10 cm2, respectively, with an X-ray energy of 6 MV. In the cranial-caudal direction, the dose profile was relatively large even if a gating signal of 50% was applied, i.e., 8.1% and 10.4% at field sizes of 5x5 cm2 and 10x10 cm2, respectively. Beam flatness without RG was much worse, i.e., 37.8% and 38.2%, at field sizes of 5x5 cm2 and 10x10 cm2, respectively. In both cases, the dose was insufficient in the expiratory direction. Although RG radiotherapy is quite useful, the margins in the inspiratory and expiratory phases should be considered based on the level of gating signal and field size in order to formulate appropriate radiotherapy planning in terms of the shifting of internal structures. To ensure accurate radiotherapy, the characteristics of the RG irradiation technique and the radiotherapy equipment must be clearly understood when this technique is to be employed in clinical practice.     

基于人体体素模型的光子外照射事故剂量重建方法研究

目的 研究光子外照射事故下人体的剂量重建方法,并在局部剂量分布层面上验证方法的准确性。方法 基于开源蒙特卡罗代码Geant4,使用国际辐射防护委员会（ICRP）103号建议书推荐的人体体素模型,研究外照射事故照射条件下的剂量重建方法,实现全身平均吸收剂量、器官吸收剂量和局部剂量分布的评价。为了对建立的方法进行验证,使用组织等效的物理仿真模型ART;通过CT扫描,建立起其分辨率为1.57 mm×1.57 mm×10.00 mm的体素模型;在标准辐射场下进行一系列热释光剂量计（TLD）照射实验,比较实验和剂量重建模拟的结果。结果 实验测量值的综合相对不确定度为10.9%,剂量重建模拟值的综合相对不确定度在非组织交界面处为7.10%,在组织交界面处为16.6%。对451个测量点位进行统计分析,模拟值除以测量值的均值为0.972,标准差为0.083 8,在0.95~1.05,0.90~1.10和0.80~1.20范围内的比例分别为49.2%,79.4%和96.4%。结论 基于人体体素模型的蒙特卡罗剂量重建方法无论在全身或器官层面,还是在局部剂量分布层面都满足实际使用的精度要求,可作为外照射事故下对受照者进行剂量评估的有力工具,为诊断和救治提供支持。     

颅脑肿瘤放射治疗时射野外器官吸收剂量体模法测量与分析

目的 在是否使用楔形板和照射野面积不同的情况下,测量和分析颅脑肿瘤放射治疗时射野外器官的吸收剂量。 方法 使用中国成人男性仿真人体模型,模拟颅脑肿瘤放射治疗,采用不使用楔形板的普通方野照射技术组和使用楔形板的三维适形照射技术（3D-CRT）组,普通方野照射技术组分别用2 cm×2 cm野和4 cm×4 cm野进行照射,3D-CRT组分别按等效方野面积分为2 cm×2 cm野和4 cm×4 cm野进行照射;使用热释光剂量计测量射野外器官的吸收剂量并进行分析。 结果 颅脑肿瘤靶区处方剂量为100 cGy时,射野外各器官吸收剂量范围为0.13~2.83 mGy。头颈部器官4 cm×4 cm野照射时的吸收剂量与2 cm×2 cm野比较,差异有统计学意义（t=-5.023,P=0.004）;胸腹部器官4 cm×4 cm野照射时的吸收剂量与2 cm×2 cm野比较,差异无统计学意义（t=-1.438,P=0.171）。普通方野照射组头颈部器官、腹部器官的吸收剂量与3D-CRT组比较,差异均有统计学意义（t_头=-2.805,P=0.038;t_腹=-11.966,P=0.000）。 结论 接受颅脑肿瘤放射治疗的患者,射野外器官吸收剂量的大小与照射野面积、是否采用楔形板照射技术有关。接受大野照射的患者,靶区邻近器官吸收剂量越大;照射野面积和处方剂量相同时,使用楔形板的照射技术相对于不使用楔形板的射野外器官的吸收剂量增大。     

Microdosimetric calculation of penumbra for biological dose in wobbled carbon-ion beams with Monte Carlo Method

In carbon-ion radiotherapy, it is important to evaluate the biological dose because the relative biological effectiveness values vary greatly in a patient’s body. The microdosimetric kinetic model (MKM) is a method of estimating the biological effect of radiation by use of microdosimetry. The lateral biological dose distributions were estimated with a modified MKM, in which we considered the overkilling effect in the high linear-energy-transfer region. In this study, we used the Monte Carlo calculation of the Geant4 code to simulate a horizontal port at the Heavy Ion Medical Accelerator in Chiba of the National Institute of Radiological Sciences. The lateral biological dose distributions calculated by Geant4 were almost flat as the lateral absorbed dose in the flattened area. However, in the penumbra region, the lateral biological dose distributions were sharper than the lateral absorbed dose distributions. Furthermore, the differences between the lateral absorbed dose and biological dose distributions were dependent on the depth for each multi-leaf collimator opening size. We expect that the lateral biological dose distribution presented here will enable high-precision calculations for a treatment-planning system.     

Estimation of absorbed dose for 2-[F-18]fluoro-2-deoxy-d- glucose using whole-body positron emission tomography and magnetic resonance imaging

The purpose of this study was to measure the cumulated activity and absorbed dose in organs after intravenous administration of 2-[F-18]fluoro-2-deoxy-d-glucose (¹⁸F-FDG) using whole-body positron emission tomography (PET) and magnetic resonance imaging (MRI). Whole-body dynamic emission scans for ¹⁸F-FDG were performed in six normal volunteers after transmission scans. The total activity of a source organ was obtained from the activity concentration of the organ measured by whole-body PET and the volume of that organ measured by whole-body T1-weighted MRI. The cumulated activity of each source organ was calculated from the time-activity curve. Absorbed doses to the individuals were estimated by the MIRD (medical internal radiation dosimetry) method using S-values adjusted to the individuals. Another calculation of cumulated activities and absorbed doses was performed using the organ volumes from the MIRD phantom and the ”Japanese reference man” to investigate the discrepancy of actual individual results against the phantom results. The cumulated activities of 18 source organs were calculated, and absorbed doses of 27 target organs estimated. Among the target organs, bladder wall, brain and kidney received the highest doses for the above three sets of organ volumes. Using measured individual organ volumes, the average absorbed doses for those organs were found to be 3.1×10^–1, 3.7×10^–2 and 2.8×10^–2 mGy/MBq, respectively. The mean effective doses in this study for individuals of average body weight (64.5 kg) and the MIRD phantom of 70 kg were the same, i.e. 2.9×10^–2 mSv/MBq, while for the Japanese reference man of 60 kg the effective dose was 2.1×10^–2 mSv/MBq. The results for measured organ volumes derived from MRI were comparable to those obtained for organ volumes from the MIRD phantom. Although this study considered ¹⁸F-FDG, combined use of whole-body PET and MRI might be quite effective for improving the accuracy of estimations of the cumulated activity and absorbed dose of positron-labelled radiopharmaceuticals. Received 23 October 1997 and in revised form 31 January 1998     

A practical SPECT technique for quantitation of drug delivery to human tumors and organ absorbed radiation dose

A practical quantitative single photon emission computed tomographic (SPECT) technique based on an empirical threshold analysis permits accurate measurements in humans of drug delivery and absorbed radiation dose. The limits of the method have been explored using a wide range of phantom volumes, concentrations, and target-to-nontarget ratios. A threshold of 43% was found to give the best results using volumes of 30 to 3,800 cc. An excellent correlation (r = .99 with a standard error of estimate [SEE] of 41 cc) was found between SPECT measured volumes and actual phantom volumes. A similarly high correlation (r = .98, SEE = 260 counts/voxel) was found in 77 measurements of concentrations between 0.01 and 3.6 microCi/cc. There was a direct relationship between the target-to-nontarget ratio of phantoms and the accuracy of volume measurements. The technique has been validated by an excellent in vivo/in vitro correlation of uptake in human tumors. The tumor cumulative concentration and tumor-to-blood ratio were used for assessment of drug delivery. In vivo quantitative measurements of the pharmacokinetics of technetium-99m (99mTc) glucoheptonate, cobalt-57 (57Co) bleomycin and platinum-195m (195mPt) cisplatin in human tumors in vivo indicates that, in contrast with tumor models in animals, there is a marked variability in drug delivery even in tumors with the same histology. Future development of labeled drugs should make it possible to use quantitative SPECT for predicting tumor response to therapy and for tailoring chemotherapy for the individual patient under treatment. SPECT quantitation of organ concentration was used for Medical Internal Radiation Dose committee (MIRD) calculations of organ absorbed radiation dose from 99mTc-labeled RBCs. Excellent in vivo/in vitro correlations were obtained between SPECT measured concentrations of blood radioactivity in the heart and in vitro measurements of blood samples. The possibilities and limitations of this technique are discussed and its use for in vivo measurement in humans of absorbed radiation dose from radiopharmaceuticals is suggested.     

Normalized data for the estimation of fetal radiation dose from radiotherapy of the breast

There can be several reasons why a pregnant patient may receive a radiological examination. It could have been a planned exposure, or the exposure might have resulted from an emergency when a thorough evaluation of pregnancy was impractical. Sometimes the pregnancy was unsuspected at the time of the examination and, with younger women being diagnosed with breast cancer, the likelihood of this will increase in radiotherapy departments. Whatever the reason, when presented with a pregnant patient who has received a radiological examination involving ionizing radiation, the dose to the fetus should be assessed based on the patient's treatment plan. However, a major source of uncertainty in the estimation of fetal absorbed dose is the influence of fetal size and position as these change with gestational age. Consequently, dose to the fetus is related to gestational age. Various studies of fetal dose during pregnancy have appeared in the literature. Whilst these papers contain many useful data for estimating fetal dose, they usually contain limited data regarding the depth and size of the fetus within the maternal uterus. We have investigated doses to the fetus from radiation therapy of the breast of a pregnant patient using an anthropomorphic phantom. Normalized data for estimating fetal doses that takes into account the fetal size (gestational age: 8-20 weeks post-conception) and depth within the maternal abdomen (4-16 cm) for different treatment techniques have been provided. The data indicate that fetal dose is dependent on both depth within the maternal abdomen and gestational age, and hence these factors should always be considered when estimating fetal dose. The data show that fetal dose can be underestimated up to about 10% or overestimated up to about 30% if the dose to the uterus is assumed instead of the actual fetal dose. It can also be underestimated up to about 23% or overestimated up to about 12% if a mean depth of 9 cm is assumed, instead of using the actual depth of the fetus within the maternal abdomen. Multi-segments sMLC technique showed consistently lower fetal doses compared with all the wedged plans employed.