放射治疗中医用直线加速器光子能量合成方法

目的：分析一种利用高低两档能量光子拟合任意中间能量光子的方法,并与现有方法进行对比。方法：百分深度剂量曲线（PDD）和离轴剂量分布曲线（OCR）是影响光子射束数据模型计算精度的两个重要特征参数。使用Varian Truebeam直线加速器模型中金标准射束数据6和15 MV射束的PDD和OCR数据,采用最小二乘拟合方法拟合中间能量10 MV射束,与金标准数据10 MV射束数据比较分析,并与其他拟合方法进行对比,证明该方法的可行性和有效性。基于三维仿真水模体数据和不同肿瘤部位的实际病例数据实验,进一步验证合成能量方法的准确性。结果：相比只考虑PDD数据的能量拟合方法,本研究方法得到的合成能量10 MV与金标准数据10 MV光子束相比,各尺寸射野下PDD的均方根误差有所增加,但均小于1%,而OCR的均方根误差明显减小（特别是20 cm以上的射野）,均小于0.5%。三维仿真水模体数据和实际患者数据测试例实验结果优于只考虑PDD数据的能量拟合方法。结论：利用PDD和OCR数据合成光子能量方法的效果较仅使用PDD数据的方法更好,合成能量光子与实际10 MV光子之间PDD和OCR差异较小,基于三维仿...     

探讨热释光在螺旋断层放射治疗系统和直线加速器中剂量标定

目的:比对热释光剂量计(TLD)在普通直线加速器（LINAC）和螺旋断层放射治疗系统（TOMO）中的剂量刻度差异,探讨TLD特性,为后续临床实测应用提供依据。方法:在6 MV光子束下,通过LINAC和TOMO对同批次TLD分别刻度。LINAC出束跳数30、50、100、150、200、300 MU;TOMO出束时间为3、5、10、15、20、30、40 s。在TLD测量位置,应用电离室交叉校准。每组测量数据为3个TLD片平均值。计算相应剂量为TLD读数的函数。将LINAC和TOMO下的TLD剂量校准曲线分别进行最小二乘法的线性模型和二次模型拟合比较,统计分析和配对t检验计算校准因子。验证相应TLD灵敏度、重复性、分散性和剂量响应等特性。结果:LINAC中,TLD发光读数[y]与照射剂量[x]关系式:[y]=94.754[x]＋0.001[x]2,R?=0.997 1;TOMO中:[y]=93.835[x]＋0.000 3[x]2,R?=0.998 2。在0.30~3.74 Gy剂量范围内,对6 MV光子束,TLD计数值与剂量呈近似线性关系。cGy剂量级同批次TLD各重复测量5次,读出平均值变化为1.48%。结论:同等能量下TOMO和LINAC的TLD刻度结果差异小于3%,符合要求。TLD线性相关性强、重复测量精度高、性能稳定,可应用于相关临床放疗剂量测量。     

国产医用直线加速器开展立体定向放射治疗的可行性研究

目的:从剂量输出、机械性能和辐射性能方面比较两种进口医用电子直线加速器和3种国产医用电子直线加速器的各项参数指标,对比分析国产医用直线加速器的技术和性能是否达到开展立体定向放射治疗的基本标准。 方法:选取两种开展过立体定向放射治疗的进口医用电子直线加速器和3种装机量较大的国产医用电子直线加速器。利用电离室和静电计在水模体上测量加速器的剂量输出性能;利用坐标纸、前指针、刻度尺等工具测量加速器机械精度;通过PIPSpro5.3.1和doselab图形分析软件测量加速器辐射性能和到位精度,从而分析固体水和EBT免冲洗胶片记录辐射野。 结果:以AAPM TG-142和中华人民共和国医药行业标准YY0832.2-2015为参考,建立一套完整的针对国产电子医用直线加速器的评价标准。检测发现国产加速器输出剂量精度、重复性、线性较高,旋转机架、准直器和治疗床辐射野等中心精度大部分小于1 mm,铅门和多叶准直器平均到位精度小于0.5 mm,两种国产加速器端对端偏差结果小于5%,说明国产加速器基本性能较好。 结论:部分国产加速器从剂量输出和治疗精度方面已达到开展立体定向放射治疗的基本要求,但开展立体定向治疗需要相关放疗单位投入更多的人力和相应设备做好加速器的质量保证和质量控制工作。     

生物医学信号的实时监控与数据采集

目的：开发基于普通微机的通用生物医学信号采集系统。方法：以Ps2104A／D／A转换卡为接口，采用C语言与汇编语言混合编程方式，自动检测微机速度并计算出调整采样频率的参数，经软件分频实现对采样频率的控制。以显示器为终端，对多路生物医学信号进行同步实时监控。结果：本系统可自动适应不同主频的普通微机，采样频率精度高，数据连续采集时间长和硬件适应能力强。结论：本系统可同步采集多路高信噪比的生物医学信号。     

基于LabVIEW的心音心电同步采集与实时播放

介绍一种通过同步采集心音心电并实时播放心音,以实现听诊与观察心音图相结合的系统.采用C8051F340为核心的硬件系统同步采集心音和心电信号,分别送到前面板的心音、心电窗口显示波形,同时用LabVIEW的声音函数播放心音,通过控制数据写入显示件和声音输出设备的时间达到同步.经过临床试验,可以实现用心电定位心音,实时播放心音.     

三维适形放射治疗同步周剂量TP方案化学治疗中晚期食管癌的临床研究

目的探讨三维适形放射治疗同步周剂量化学治疗在中晚期食管癌治疗中的近期有效率、不良反应及生存率。方法选择80例中晚期食管癌患者,根据入选标准进入研究,其中男性52例,女性28例;年龄56～82岁,中位年龄66岁。随机分为2组,三维适形放射治疗同步周剂量TP方案化学治疗组（放化疗组）28例;单纯三维适形放射治疗组（单放组）52例。放化疗组采用三维适形放射治疗,常规分割,每次2 Gy,1次/天,5天/周,放疗剂量60～66 Gy,同步给予TP方案,组成及用法：顺铂20～30mg/m2,第1、2天和第8、9天静脉滴注;紫杉醇90 mg/m2,第1天、第8天静脉滴注;28 d为1个周期,共2～4个周期。单放组采用单纯三维适形放射治疗,放射剂量同放化疗组。结果放化疗组近期有效率为96.4%,单放组为96.2%,两组比较,差异无统计学意义（P〉0.05）。放化疗组1年、2年、3年生存率分别为73.5%、68.8%、49.7%,1年、2年、3年局部控制率分别为86.8%、72.7%、60.3%;单放组1年、2年、3年生存率分别为69.5%、50.9%、35.6%,1年、2年、3年局部控制率分别为71.6%、55.4%、47.8%。两组患者1年生存率差异无统计学意义,2年、3年生存率及1年、2年、3年局部控制率差异均有统计学意义。放化疗组不良反应主要是放射性食管炎、消化道反应和血液毒性,患者均能耐受。结论三维适形放射治疗同步周剂量TP方案化学治疗对中晚期食管癌近期疗效及生存率较好,虽不良反应增加但患者可以耐受。     

同步加量调强与常规调强放射治疗食管癌的效果比较

目的：探讨同步加量调强与常规调强放射治疗食管癌的效果。方法：回顾分析149例食管癌患者的临床资料,根据治疗方式不同将其分为同步组（n=77）和常规组（n=72）,同步组患者予以同步加量调强放射治疗,常规组患者予以常规调强放射治疗。比较两组患者治疗后临床疗效、血清肿瘤因子鳞状细胞癌抗原（SCC）、糖类抗原125(CA125)、癌胚抗原（CEA）水平、体力状况评分（Karnofsky评分）、生活质量评分（SF-36评分）、不良反应。结果：治疗后,同步组临床总有效率高于常规组（93.51%vs 81.94%, P<0.05）;同步组血清肿瘤因子SCC、CA125、CEA水平均低于常规组（P<0.05）;同步组Karnofsky评分和SF-36评分均高于常规组（P<0.05）;同步组不良反应轻于常规组。结论：同步加量调强与常规调强放射治疗食管癌均有一定临床效果,但相较于常规调强放射治疗,同步加量调强放射治疗对食管癌患者临床效果更为理想,能有效控制血清肿瘤因子高表达,改善预后,且不良反应相对较少。     

基于80c196单片机的实时24小时动ECG记录分析仪的研究

本文介绍了一种２４小时双通道固态记录与实时分析于一体的便携式心电记录分析仪的设计。仪器以８０ｃ１９６单片机为核心，配以大规模单片机接口电路芯片ＰＳＤ４０３使得整机体积小且功耗低，该仪器的显著特点是无须连接ＰＣ机进行后处理即可独立联接打印机输出动态心电分析监护报告，报警事件报告和心率变异分析报告。借助于ＭＩＴ心电数据库，采用数模转换后的输出信号作为模拟心电波对样机进行检验，其结果表明该仪器硬件合理实用，分析算法的实时性和准确性都能够满足要求。经临床２２例验证，各设计指标均已达到要求     

医用直线加速器楔形因子与射野依赖性研究

楔形因子（ＷｅｄｇｅＦａｃｔｏｒＷＦ）随射野大小变化在放疗照射剂量确定中是非常重要的参量变化规律。不同加速器其机头设计不同则ＷＦ不同。笔者对两台加速器（ＰＨＩＬＩＰＳＳＬ７５和ＶＡＲＩＡＮＣＬ１８００）ＷＦ随射野变化关系进行了研究，发现ＶＡＲＩＡＮＣＬ１８００ＷＦ随射野改变＜±１％，ＰＨＩＬＩＰＳＳＬ７５则ＷＦ随射野变化有±７％的改变。类比于总散射因子（Ｓｐ，ｃ）的定义，我们定义因子Ｓｗ来表征楔形板因子对射野大小的依赖关系。     

直线加速器注入电流与照射野对称性的关系研究

目的：电子直线加速器的注入电流在使用中会发生改变。从而对剂量学参数照射野对称性产生影响。作者对注入电流的变化规律及其造成照射野对称性改变的程度进行实验研究。探讨加速器照射野质量控制的要求。方法：手动模拟加速器注入电流的改变。在照射野对称性良好的注入电流工作点附近设置正负模拟值，以胶片法测最和分析对应的照射野对称性改变。结果：注入电流的数值在加速器的枪靶方向不会影响照射野对称性的质量。在左右方向的对称性偏差值受注入电流数值的影响近似为线性关系，当注入电流偏离中值0.2A时，相应的对称性误差接近3％。作者工作部门的正常工作量下注入电流每月约下降（0．1～0．2）A。结论：检测加速器注入电流的改变可以提示照射野对称性的误差。照射野剂量特性和注入电流应纳入每周的质控检验内容。     

Stability of a mobile electron linear accelerator system for intraoperative radiation therapy

The flexibility of mobile electron accelerators, which are designed to be transported to an operating room and plugged into a normal 3-phase outlet, make them ideal for use in intraoperative radiation therapy. However, their transportability may cause trepidation among potential users, who may question the stability of such an accelerator over a period of use. In order to address this issue, we have studied the short-term stability of the Mobetron system over 20 daily quality assurance trials. Variations in output generally varied within +/-2% for the four energies produced by the unit (4, 6, 9, and 12 MeV) and changes in energy produced an equivalent shift of less than 1 mm on the depth-dose curve. Hours of inactivity, with the Mobetron powered on for use either throughout the day or overnight, led to variations in output of about 1%. Finally, we have tested the long-term stability of the absolute dose output of the Mobetron, which showed a change of about 1% per year.     

医科达加速器的剂量监测与控制系统

从机器物理和电子工程双重角度,系统全面地解析医科达直线加速器的剂量监测与控制系统全貌。剖析电离室的构造特征以及与构造特征相对应的故障发生机理,阐释漏电与短路的区别,极板间灰尘引起尖端放电打火导致极板穿孔与裂纹,极板的耐辐射性与辐照老化导致的裂纹。总结电离室漏电、短路、开路、穿孔与裂纹5种因素的原因与故障现象。提出并说明等效灵敏体积的概念,阐释剂量监测与控制的本质是保持配对收集极板之间的电离电流相等。阐释剂量均匀性的保证机制和能量稳定机制,阐述完整的剂量学质量控制调整方法和该系统的维护维修方法。     

Buildup region and skin-dose measurements for the Therac 6 linear accelerator for radiation therapy

Buildup and surface-dose measurements were taken for the 6 MV photon beam from a Therac 6 linear accelerator manufactured by Atomic Energy of Canada Limited (AECL) with and without a lucite blocking tray in place. Further measurements were made with a copper filter designed to reduce secondary electrons emitted by photon interactions with the Lucite tray. The results are discussed in relation to skin-sparing for radiation therapy patients. The measurements were made with a fixed volume PTW parallel-plate ionization chamber and corrected to zero-chamber volume. The results were found to be consistent with similar measurements taken with a variable volume extrapolation chamber.     

Neutron production from a mobile linear accelerator operating in electron mode for intraoperative radiation therapy

Intraoperative electron beam radiotherapy is increasingly performed using mobile linac delivering therapeutic radiation doses in unshielded operating rooms. While no special neutron-shielding problem should arise for operation at 10 MeV or less, it is not clear whether this holds true for operation at higher energies. This paper reports the measured neutron production from a Mobetron mobile electron linac, operated at 12 MeV, and compares the results with those from a conventional linac, also operated at 12 MeV in electron mode. Neutron leakage measurements were performed by means of passive bubble detectors in the scattering foil, patient and floor planes. Neutron dose equivalent rates per unit of electron dose delivered by the Mobetron at its normal treatment distance (50 cm SSD) were 0.33 microSv Gy(-1) at the accelerator head, 0.18 microSv Gy(-1) in the patient plane at 15 cm from the beam axis and 0.31 microSv Gy(-1) at the floor plane, on the beam axis and under the beam stopper. For a weekly workload of 250 Gy, the weekly neutron dose equivalents at 12 MeV for the Mobetron at a distance of 300 cm from the scattering foil were 14.3 and 1.7 microSv/week for floor below and adjoining areas on the same floor, respectively. Neutron dose equivalent rates generated from Mobetron are at least one order of magnitude lower than ones produced by a conventional linac operated at the same energy in electron mode. Mobetron can be used at 12 MeV in an unshielded operating room for a weekly workload of up to 250 Gy if the bremsstrahlung x-rays are shielded to negligible levels.     

Intraoperative radiation therapy using a mobile electron linear accelerator: field matching for large-field electron irradiation

Intraoperative radiation therapy (IORT) consists of delivering a large, single-fraction dose of radiation to a surgically exposed tumour or tumour bed at the time of surgery. With the availability of a mobile linear accelerator in the OR, IORT procedures have become more feasible for medical centres and more accessible to cancer patients. Often the area requiring irradiation is larger than what the treatment applicators will allow, and therefore, two or more adjoining fields are used. Unfortunately, the divergence and scattering of the electron beams may cause significant dose variations in the region of the field junction. Furthermore, because IORT treatments are delivered in a large single fraction, the effects of underdosing or overdosing could be more critical when compared to fractionated external beam therapy. Proper matching of the fields is therefore an important technical aspect of treatment delivery. We have studied the matching region using the largest flat applicator available for three different possibilities: abutting the fields, leaving a small gap or creating an overlap. Measurements were done using film dosimetry for the available energies of 4, 6, 9 and 12 MeV. Our results show the presence of clinically significant cold spots for the low-energy beams when the fields are either gapped or abutted, suggesting that the fields should be overlapped. No fields should be gapped. The results suggest that an optimal dose distribution may be obtained by overlapping the fields at 4 and 6 MeV and simply abutting the fields at 9 and 12 MeV. However, due to uncertainties in the placement of lead shields during treatment delivery, one may wish to consider overlapping the higher energy fields as well.     

Levels of leakage radiation from electron collimators of a linear accelerator

The leakage radiation from electron applicators used with our linear accelerator has been measured. For the applicators 6 X 6 to 25 X 25 cm size, the leakage was measured in the plane of the patient and on the sides of the applicators with the available electron energies of 6, 9, 12, 15 and 18 MeV. The levels were significant. The highest leakage on the side was for the combination of 6 X 6-cm applicator and 9-MeV electrons (32%) and in the plane of the patient for 25 X 25-cm applicator with 18 MeV (10%) relative to the peak dose. Adding lead 1-2 mm, at appropriate locations inside the applicators has reduced the leakages to acceptable levels without affecting the beam parameters.     

Dose linearity and uniformity of a linear accelerator designed for implementation of multileaf collimation system-based intensity modulated radiation therapy

The dose linearity and uniformity of a linear accelerator designed for multileaf collimation system-(MLC) based IMRT was studied as a part of commissioning and also in response to recently published data. The linear accelerator is equipped with a PRIMEVIEW, a graphical interface and a SIMTEC IM-MAXX, which is an enhanced autofield sequencer. The SIMTEC IM-MAXX sequencer permits the radiation beam to be " ON" continuously while delivering intensity modulated radiation therapy subfields at a defined gantry angle. The dose delivery is inhibited when the electron beam in the linear accelerator is forced out of phase with the microwave power while the MLC configures the field shape of a subfield. This beam switching mechanism reduces the overhead time and hence shortens the patient treatment time. The dose linearity, reproducibility, and uniformity were assessed for this type of dose delivery mechanism. The subfields with monitor units ranged from 1 MU to 100 MU were delivered using 6 MV and 23 MV photon beams. The doses were computed and converted to dose per monitor unit. The dose linearity was found to vary within 2% for both 6 MV and 23 MV photon beam using high dose rate setting (300 MU/min) except below 2 MU. The dose uniformity was assessed by delivering 4 subfields to a Kodak X-OMAT TL film using identical low monitor units. The optical density was converted to dose and found to show small variation within 3%. Our results indicate that this linear accelerator with SIMTEC IM-MAXX sequencer has better dose linearity, reproducibility, and uniformity than had been reported.     

Mechanical and radiation isocenter coincidence: an experience in linear accelerator alignment.

As part of the commissioning procedure of a linear accelerator at our cancer center, the defining laser lines were aligned with the optical and radiation isocenter of the linac. When a mechanical checkout jig was set up at the same point, a discrepancy of 4 mm resulted when the gantry was moved from 0 degrees to 180 degrees. Extensive measurements, some with custom-designed devices, confirmed the observations and provided an explanation. Even though the mechanical isocenter is within the specified tolerance of 1-mm radius, the clinically observable discrepancy of 4-mm results from the noncoincidence of the mechanical and radiation isocenters. The clinical significance of the final setup is discussed and future commissioning procedures are recommended.     

Daily monitoring of linear accelerator beam parameters using an amorphous silicon EPID

An amorphous silicon EPID has been investigated to test its suitability as a daily check device for linac output and to provide daily monitoring of beam profile parameters such as flatness, symmetry, field size and wedge factor. Open and wedged 6 and 8 MV photon beams were collected on a daily basis for a period of just over a year and analysed in software to determine daily values of these parameters. Daily output results gave agreement between EPID measured dose and ion chamber measurements with a standard deviation of 0.65%. Step changes in flatness, symmetry and field size were readily detected by the EPID and could be correlated with adjustments made on service days and QC sessions. The results could also be used to assess the long term beam stability. Recalibration of the EPID required new baseline values of the parameters to be set. Wedge factors measured at one collimator angle proved stable but sensitive to changes in beam steering. The EPID proved to be a useful daily check device for linac output which can simultaneously be used for daily monitoring of beam profiles and field sizes.