Accurate Monte Carlo simulations for nozzle design, commissioning and quality assurance for a proton radiation therapy facility

Monte Carlo dosimetry calculations are essential methods in radiation therapy. To take full advantage of this tool, the beam delivery system has to be simulated in detail and the initial beam parameters have to be known accurately. The modeling of the beam delivery system itself opens various areas where Monte Carlo calculations prove extremely helpful, such as for design and commissioning of a therapy facility as well as for quality assurance verification. The gantry treatment nozzles at the Northeast Proton Therapy Center (NPTC) at Massachusetts General Hospital (MGH) were modeled in detail using the GEANT4.5.2 Monte Carlo code. For this purpose, various novel solutions for simulating irregular shaped objects in the beam path, like contoured scatterers, patient apertures or patient compensators, were found. The four-dimensional, in time and space, simulation of moving parts, such as the modulator wheel, was implemented. Further, the appropriate physics models and cross sections for proton therapy applications were defined. We present comparisons between measured data and simulations. These show that by modeling the treatment nozzle with millimeter accuracy, it is possible to reproduce measured dose distributions with an accuracy in range and modulation width, in the case of a spread-out Bragg peak (SOBP), of better than 1 mm. The excellent agreement demonstrates that the simulations can even be used to generate beam data for commissioning treatment planning systems. The Monte Carlo nozzle model was used to study mechanical optimization in terms of scattered radiation and secondary radiation in the design of the nozzles. We present simulations on the neutron background. Further, the Monte Carlo calculations supported commissioning efforts in understanding the sensitivity of beam characteristics and how these influence the dose delivered. We present the sensitivity of dose distributions in water with respect to various beam parameters and geometrical misalignments. This allows the definition of tolerances for quality assurance and the design of quality assurance procedures.     

4D Monte Carlo simulation of proton beam scanning: modelling of variations in time and space to study the interplay between scanning pattern and time-dependent patient geometry

When dosimetric effects in time-dependent geometries are studied, usually either the results of individual three-dimensional (3D) calculations are combined or probability-based approaches are applied. These methods may become cumbersome and time-consuming if high time resolution is required or if the geometry is complex. Furthermore, it is difficult to study double-dynamic systems, e.g., to investigate the influence of time-dependent beam delivery (i.e., magnetically moving beam spots in proton beam scanning) on the dose deposition in a moving target. We recently introduced the technique of 4D Monte Carlo dose calculation to model continuously changing geometries. In intensity modulated proton therapy, dose is delivered by individual pristine Bragg curves. Dose spots are positioned in the patient by varying magnetic field and beam energy. If the movement of these dose spots occurs during significant respiratory motion, interplay effects can take place. Because of the inhomogeneity of individual subfields, the consequences of motion can be more severe than in conventional proton therapy. We demonstrate how the technique of 4D Monte Carlo can be used to study interplay effects in proton beam scanning. Time-dependent beam delivery to a changing patient geometry is simulated in a single 4D dose calculation. Interplay effects between respiratory motion and beam scanning speed are demonstrated.     

钛颗粒负荷对成骨细胞白细胞介素6生成的影响

磨损碎屑颗粒所诱发的无菌性松动是人工关节置换术后最常见的并发症.研究表明,假体-骨界面的骨组织细胞吞噬磨屑颗粒后,以自分泌或旁分泌的方式释放细胞间介质因子,而引起假体旁骨改建紊乱,导致假体松动.为了探明不同直径的磨屑颗粒对细胞释放细胞间介质因子的影响,本研究采用3种不同直径(mean sizeφ0.9 μm、φ2.7μm、φ6.9 μm)的钛颗粒,在浓度分别为0.25wt%,0.1wt%,0.05wt%下与兔成骨细胞共孵育4、8、12、24、36、48 h后,检测各组细胞白介素6(IL-6)分泌的变化情况.结果表明,3种钛颗粒均能刺激成骨细胞分泌IL-6因子,但其上调作用因不同直径,不同负荷浓度,不同负荷时间而有所不同.随着浓度增加和时间的推移,φ2.7μm和φ6.9 μm钛颗粒对IL-6生成的上调作用持续升高,而φ 0.9 μm钛颗粒的上调作用却呈先升高后快速下降的双相变化过程.结果提示磨屑颗粒能明显刺激细胞释放细胞间介质因子IL-6,而颗粒直径大小不同,上调IL-6的程度有所不同,使得细胞间介质因子影响假体旁骨改建紊乱的机制有所不同,这种由细胞因子介导的信号传递机制若进一步深入研究必将有助于人工关节材质的优化选择及临床预防用药指导.     

冬春季儿童、婴幼儿哮喘急性发作的呼吸道病毒病原学特征及临床研究

目的 了解北京地区冬春季儿童、婴幼儿哮喘急性发作时的呼吸道常见病毒——呼吸道合胞病毒（RSV）、流感病毒（IFA1、IFA3、IFB）、副流感病毒（PIF1、PIF3）、腺病毒（ADV）的感染情况及与临床症状和嗜酸细胞的关系。方法 对2000年11月至2001年3月及2001年11月至2002年3月，来首都儿科研究所哮喘中心就诊的哮喘急性发作的患儿176名，采用病毒分离及间接免疫荧光法，对鼻咽分泌物（nasopharyngeal secretions，NPS）中七种病毒抗原进行监测，并同时记录临床症状和用药情况及进行鼻咽分泌物和外周血中嗜酸细胞计数。结果 176例哮喘急性发作患儿NPS中，79例检测出病毒，阳性率为44．9％。其中RSV 66例，感染率为37．5％、IF7例（4．0％）、ADV6例（3．4％）及PIF4例（2．3％）。RSV占79例病毒感染患儿的83．5％；4例患儿同时测定出RSV和其他病毒混合感染。这些病毒在哮喘急性发作的患儿中检出率与年龄呈反比，小年龄组的患儿病毒感染多；检出病毒的患儿病情重，伴发热的患儿显著多于未检查出病毒的患儿。病毒感染与非感染组的NPS中嗜酸细胞数目检测无明显差别；但血中嗜酸细胞的数目，病毒检出阳性的患儿，较病毒测定阴性的患儿明显减少（t=2．676，P〈0．001）。结论 北京地区冬季近半数哮喘急性发作的患儿呼吸道病毒检测阳性，其中RSV是婴幼儿哮喘发作的主要感染病毒，引起较严重的临床症状；病毒检出阳性的患儿，血中嗜酸细胞的数目明显减少。     

青春期糖尿病雄鼠血清和性腺血管紧张素转换酶活性变化

４０日龄雄性Ｗｉｓｔａｒ大鼠２１只，分为对照（Ｃ）组，腹腔内注射赋形剂和糖尿病（Ｄ）组，腹腔内注射链脲菌素（ｓｔｒｅｐｔｏｚｏｔｏｃｉｎ，ＳＴＺ），５５ｍｇ／ｋｇ体重，观察６０天。结果表明，Ｄ组大鼠的睾丸、附睾、附睾尾重量显著低于Ｃ组（Ｐ＜０．０１）；Ｄ组附睾尾精子计数显著少于Ｃ组（Ｐ＜０．００１）。ＡＣＥ活性测定结果表明，Ｄ组睾丸和附睾尾组织ＡＣＥ活性显著低于Ｃ组（Ｐ＜０．０５），而血清ＡＣＥ显著高于Ｃ组（Ｐ＜０．０１），相关检验显示，附睾重量，附睾尾精子计数与附睾尾ＡＣＥ水平呈显著正相关（Ｐ＜０．０１），与血清ＡＣＥ呈显著负相关（Ｐ＜０．０５，Ｐ＜０．０１）。     

脑缺血模型大鼠海马CRF、PKC蛋白表达研究

目的： 观测脑缺血再灌模型大鼠海马神经细胞CRF、PKC蛋白表达变化。方法: 采用免疫组化技术检测脑缺血模型大鼠于再灌2 h、6 h、24 h时海马神经细胞CRF、PKC蛋白表达量，CRF拮抗剂对照。结果: (1)CRF：假手术组海马区可见少量阳性细胞；模型组见大量阳性细胞，着色深，随时间延长增多。拮抗剂组阳性表达较少，着色较浅。模型组和盐水组CRF蛋白阳性表达面积均显著高于假手术组和CRF拮抗剂组（P<0.01）。(2)PKC：假手术组海马区阳性表达颗粒少，模型组和盐水组见大量阳性表达颗粒，拮抗剂组阳性表达颗粒稀疏。模型组和盐水组CRF蛋白阳性表达面积均显著高于假手术组和CRF拮抗剂组（P<0.01）。结论: 脑缺血再灌诱导CRF、PKC蛋白高表达是导致海马神经细胞迟发性死亡的重要因素；CRF蛋白激活PKC蛋白表达可能是CRF诱导缺血后神经组织损伤的机制。     

Rice as a model for centromere and heterochromatin research

Rice (Oryza sativa) has become an important model plant species in numerous research projects involving genome, molecular and evolutionary biology. In this review we describe the reasons why rice provides an excellent model system for centromere and heterochromatin research. In most multicellular eukaryotes, centromeres and heterochromatic domains contain long arrays of repetitive DNA elements that are recalcitrant to DNA sequencing. In contrast, three rice centromeres and the majority of the cytologically defined heterochromatin in the rice genome have been sequenced to high quality, providing an unparalleled resource compared to other model multicellular eukaryotes. Most importantly, active genes have been discovered in the functional domains of several rice centromeres. The centromeric genes and sequence resources provide an unprecedented opportunity to study function and evolution of centromeres and centromere-associated genes.     

Inhibitory effect and mechanism of chuanxiongzine on multiplication of VSMC

Objective: To study the inhibitory effect of chuanxiongzine on vascular smooth muscle cell (VSMC) proliferation and explore its molecular biology basis. Methods: we selected the VSMC cultured 4～8 generation from rat aorta thoracalis as research object.The objects were divided into four groups( Ⅰ )control group, ( Ⅱ )chuanxiongzine(50 μg/ml)group, ( Ⅲ )chuanxiongzine (100 μg/ml) group and( Ⅳ ) chuanxiongzine (200 μg/ml) group. The inhib itory effect of chuanxiongzine on VSMC proliferation was investigated by cell counting, MTT and 3H-TdR incorporation assay. In order to illuminate the molecular biology mechanism of chuanxiongzine inhibiting VSMCs proliferation, the expression of proliferating cell nuclear antigen (PCNA) and C-myc were detected.Results: Chuanxiongzine could inhibit the proliferation of VSMC significantly in a dose- and time-dependent manner, compared with control group (P ＜ 0.05). The expression of PCNA and c-myc were inhibited obviously and correlated with the concentration of chuanxiongzine (P ＜ 0.05). Conclusion: Chuanxiongzine may play a considerable role in VSMC proliferation process. The inhibitory effect of chuanxiongzine in a dose- and time-dependent manner can be realized via down regulating the expression of PCNA and c-myc. In this study, The great theoretical fundament about Chinese medicine, which is used to treat atherosclerosis (AS), has been obtained.     

儿科对碳青霉烯类耐药铜绿假单胞菌产金属酶的研究

目的 了解目前儿科对碳青霉烯类抗生素耐药铜绿假单胞菌产金属酶的情况。方法 本研究收集了2003年12月至2005年11月，北京儿童医院住院患儿中分离出对碳青霉烯类抗生素耐药的铜绿假单胞菌59株。使用E试验法检测金属酶的耐药表型，PCR技术检测编码金属酶的IMP、VIM、SPM和GIM4种基因型。结果 本研究59株对碳青霉烯类抗生素耐药铜绿假单胞菌中，29株金属酶耐药表型结果阳性，占49．2％。39株金属酶基因型阳性，占66．1％，其中扩增出IMP型阳性35株，占89．7％，VIM型阳性4株，占10．3％。未检测出SPM和GIM型金属酶。对哌拉西林、哌拉西林-他唑巴坦产金属酶不敏感率高于非产金属酶菌株，差异有统计学意义（P〈0．05）。对产金属酶菌株β-内酰胺类抗生素头孢噻肟、头孢哌酮、头孢他啶、头孢吡肟、头孢哌酮-舒巴坦的MIC90均达到256μg／ml，MIC90均大于256μg／ml，高于非产金属酶菌株。结论 从本研究分离的菌株显示儿科铜绿假单胞菌产金属酶率高于成人报道，产金属酶是儿科分离对碳青霉烯类抗生素耐药铜绿假单胞菌的重要耐药机制。且以产IMP型金属酶为主，少部分产VIM型金属酶。产金属酶菌株对β-内酰胺类抗生素耐药比非产金属酶菌株更严重，尤其对哌拉西林和哌拉西林-他唑巴坦耐药性高。E试验法易用于铜绿假单胞菌产金属酶的初步筛选，但不能单独作为检测铜绿假单胞菌产生金属酶的确证性试验。     

HLA-DRB1~* 1501与我国北方汉族儿童结核病的易感性研究

为了研究中国北方儿童结核病与HLAⅠ类基因的关联,我们采用PCR-SSO方法检测了97例北方汉族结核患儿和91例正常对照的HLA-DRBl,DQAl,DQBl等位基因.发现中国北方汉族儿童结核病与HLA-DRBl·1501有显著关联.进一步比较DR分子结构发现β链第86位氨基酸对结核病的易感性可能有重要意义.