医用直线加速器矩形野散射因子的简便计算方法

 目的　建立一种适合于临床应用的加速器散射因子 Sc.p的简便计算方法。方法　 ( 1 )通过测量方野的散射因子 ,建立方野散射因子与射野边长的拟合公式 ;( 2 )利用 Kim的经验公式 ,计算矩形野的等效方边长 ;( 3)应用已拟合的方野散射因子公式计算矩形野的散射因子 ,并与矩形野的测量结果进行比较。结果　采用该方法计算医用加速器散射因子的最大误差在 0 .5%以下 ,而采用面积 -周长比原理确定的等效方边长 ,最大误差达到 3%左右。结论　该方法可用于简便快速地确定方野和矩形野的散射因子 ,精确度高 ,完全可应用于临床.     

电子束照射野面积对中心轴剂量和输出因子的影响

目的探讨电子束照射野挡块对中心轴剂量和输出因子的影响.方法用瑞典Scaditronix公司生产的RFA-300型三维水箱及P型硅半导体探头对瓦里安2100C和2300C/D直线加速器的多种能量电子束进行了中心轴百分深度剂量(PDD)扫描,并测量了照射野输出因子.结果测得的PDD数据表明,电子束深度剂量对照射野铅挡大小有某种程度的依赖性,一般倾向是当照射野减小时表面剂量增大,治疗深度减小,最大剂量深度(R100)向表面移.这些变化在高能时最为明显.输出因子的测量结果说明,对不同能量电子束在不同限光筒条件下,输出因子随照射野铅挡大小改变的情况不尽相同.结论临床治疗时使用的限光筒大小要尽量与实际照射野面积接近,在使用铅挡构成很小的照射野(如<6cm×6cm)时,应实际测量输出因子,以减少剂量误差.     

直线加速器注入电流变化对照射野对称性的影响

[目的]探讨电子直线加速器的注入电流改变对剂量学参数照射野对称性产生的影响.[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,以胶片法测量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左右方向不会影响照射野对称性的质量,在枪靶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200mA时,相应的对称性误差接近3%.[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,经常性监视照射野剂量特性和注入电流应纳入每周的质控检验内容.     

SIEMENS 6MV X刀剂量测量

用P型半导体探测器测量X刀4mm~41．2mm射野的输出因子Scp、体模散射因子Sp、百分深度剂量PDD和离轴比曲线OAR；用0．1cc电离室测量射野的输出因子、体模散射因子和组织最大剂量比（TMR）。通过两者的比较及与已发表文献比较，对结果给予评价。结果显示：用小型半导体探测器测量X刀，可获得准确的结果；测量百分深度剂量获得TMR比用电离室直接测量TMR更快捷更简便；0．1cc电离室测量射野输出因子，电离室直径要小于射野直径的一半，否则将引起较大误差。     

不同探测器测量射波刀输出因子比较分析

目的 比较分析5种不同探测器测量射波刀输出因子,以选择适合的探测器。方法分别使用电离室探测器PTW30013、PTW31010,半导体探测器PTW 60017、60018,宝石探测器PTW60019及EBT3胶片测量射波刀12个孔径准直器的输出因子。比较分析不同探测器及探测器放置方向测量的输出因子。结果 准直器孔径>30 mm时5种探测器测量的输出因子差异<1%,准直器孔径<30 mm时不同探测器测量结果差异较大,准直器孔径越小差异越大。与胶片测量结果比较,PTW60019与胶片的一致性最好,偏差<2%。半导体探测器测量结果稍高,电离室探测器测量结果过小。探测器放置方向不同,输出因子测量结果不同。PTW60019探测器平行射野中心轴放置时,测量的输出因子比垂直射野中心轴放置的结果偏低,PTW31010探测器测量结果相反。结论 准直器孔径>30 mm时PTW31010、PTW60017、60018及PTW60019可直接用于射波刀输出因子测量,准直器孔径<30 mm时需要对上述探测器的测量结果进行修正。PTW30013不适合小野输出因子测量。     

60Co机准直器散射因子(Sc)的性质

目的测量６０Ｃｏ机准直器散射因子（Ｓｃ）的性质，为临床使用提供依据。材料与方法在两种类型６０Ｃｏ机上，用指形电离室测量Ｓｃ随各种因素的变化规律。测量时，电离室的轴线与照射野的射线束轴重合。结果获得了Ｓｃ与源皮距的关系数据。分析了不同矩形野Ｓｃ的变化，挡块对Ｓｃ影响等。结论在一般照射野大小，Ｓｃ与源皮距无关，并可用二次函数来拟合Ｓｃ随照射野大小的变化。挡块及有机玻璃托盘对Ｓｃ影响可忽略。但在大野时Ｓｃ略有不同。根据测量的数据提出了矩形照射野的Ｓｃ等效方野的计算公式     

Elekta直线加速器全碳纤维六维治疗床床板对后斜野放疗剂量的影响

[目的]探讨Elekta Synergy直线加速器全碳纤维六维治疗床床板对后斜野放疗剂量的影响。[方法]采用等中心技术测量,深度6cm,射野10cm×10cm,能量6MV和15MV,每个射野照射剂量100MU,机架角间隔5°设一个野,设两组射野,一组射野机架角为270°至0°,另一组射野机架角为90°至180°,两组射野为等中心对穿野;准直器和治疗床角度为0°。将标准固体水模中轴与治疗床中心纵轴重合置于治疗床上,用PTW剂量仪0.6CCFarmer电离室比对测量,计算出全碳纤维六维治疗床主床板、延长板及其衔接处对后斜野放疗剂量的衰减。[结果]6MV能量,全碳纤维六维治疗床主床板对剂量的衰减在1.7%～6.0%;延长板对剂量的衰减在1.8%～6.1%;延长板和主床板衔接处对剂量的衰减在8.4%～25.6%。15MV能量,全碳纤维六维治疗床主床板对剂量的衰减在1.1%～4.8%;延长板对剂量的衰减在1.1%～4.7%;延长板和主床板衔接处对剂量的衰减在6.0%～19.8%。[结论]全碳纤维六维治疗床主床板及其体部延长板对剂量的衰减接近,进行常规二维或三维适形治疗时后斜野应做剂量修正;因延长板和主床板衔接处都为床板的边框且有固定螺栓,故衰减比较大,在治疗摆位时应避免射野穿过衔接处。同一能量由于机架角度的改变穿过床板的厚度不同,不同厚度床板衰减因子也不同,随床板厚度的增加衰减因子减小;不同能量同一位置床板衰减也不同,能量增加衰减变小。计划系统计算模型没有加入治疗床板的修正,后斜野由于床板对剂量的衰减,一方面会导致靶区欠剂量,另一方面会增加皮肤剂量,应引起临床治疗的注意。     

用来评估医用电子直线加速器头部周围泄漏辐射剂量的两种方法的比较(英文)

Objective:The aim of this study was to measure the leakage by two methods with ion chamber and ready packs film,and to investigate the feasibility and the advantages of using two dosimetry methods for assessing leakage radiation around the head of the linear accelerators.Methods:Measurements were performed using a 30 cm3ion chamber;the gantry at 0°,the X-ray head at 0°,the field size at between the central axis and a plane surface at a FSD of 100 as a reference,a series of concentric circles having radii of 50,75,and 100 cm with their common centre at the reference point.The absorbed dose was measured at the reference point,and this would be used as the reference dose.With the diaphragm closed,the measurements were taken along the circumference of the three circles and at 45°intervals.Results:Leakage radiations while the treatment head was in the vertical position varied between 0.016%–0.04%.With the head lying horizontally,leakage radiation was the same order magnitude and varied between 0.02%–0.07%.In the second method,the verification was accomplished by closing the collimator jaws and covering the head of the treatment unit with the ready pack films.The films were marked to permit the determination of their positions on the machine after exposed and processed.With the diaphragm closed,and the ready packs films around the linear accelerator the beam turned on for 2500 cGy(2500 MU).The optical density of these films was measured and compared with this of the reference dose.Leakage radiation varied according to the film positions and the magnitude of leakage was between 0.005%–0.075%.Conclusion:The differences between the values of the leakage radiation levels observed at different measurement points do not only reflect differences in the effective shielding thickness of the head wall,but are also related to differences in the distances between the target and the measurement points.The experimental errors involved in dosimetric measurement also contribute to such differences.     

An investigation of a model of percentage depth dose for irregularly shaped fields

A significant component of the total dose delivered to tumor and surrounding tissue during a radiation treatment arises from the scattering of the primary beam. Accounting for this component accurately and efficiently is a necessity. In this study we investigate a method for calculating the phantom-scatter contributions to the total dose by simple summation of scatter dose from a set of individual triangles that span an irregular field. The calculation of phantom scatter is based on a two-parameter model, which is applicable to regions where electron equilibrium is established. The two physical parameters are the dose-averaged linear attenuation coefficient and the beam-hardening coefficient. The advantage of this model is that it is a natural method when an irregular field is shaped by a multi-leaf collimator (MLC). Accuracy is not compromised by the triangulation since the irregular field is defined by the straight edges of the MLC leaves. The model predicts the percent depth dose with acceptable accuracy for any arbitrary shape of fields. We report on results for 6- and 18-MV photon beams and for a number of irregularly shaped fields.     

三维水箱不同测试条件对数据采集结果的影响和分析

目的:评价三维水箱作为加速器各项参数的调试和验收以及治疗计划系统数据采集的作用。方法:通过多组实验,改变在使用三维水箱测量时不同的测量条件和测试工具,总结对测量结果的影响。同时进一步分析其对于放疗质控的优劣对比。总结最佳的扫描方式。结果:不同的测量条件对测量结果有一定的差异。选择最佳的扫描模式和扫描工具对于测量的精度具有重要意义,会明显提高放射治疗的剂量精度。结论:在水箱数据采集和质控工作中,如果能够得到进一步的信息,水箱的测试结果将会更加精准、完善。     

Determination of recombination and polarity correction factors,kS and kP,for small cylindrical ionization chambers PTW 31021 and PTW 31022 in pulsed filtered and unfiltered beams

The aim of this technical communication is to provide correction factors for recombination and polarity effect for two new ionization chambers PTW PinPoint 3D (type 31022) and PTW Semiflex 3D (type 31021). The correction factors provided are for the (based on the) German DIN 6800-2 dosimetry protocol and the AAPM TG51 protocol. The measurements were made in filtered and unfiltered high-energy photon beams in a water equivalent phantom at maximum depth of the PDD and a field size on the surface of 10 cm × 10 cm. The design of the new chamber types leads to an ion collection efficiency and a polarity effect that are well within the specifications requested by pertinent dosimetry protocols including the addendum of TG-51. It was confirmed that the recombination effect of both chambers mainly depends on dose per pulse and is independent of the filtration of the photon beam.     

Improvement of the penumbra for small radiosurgical fields using flattening filter free low megavoltage beams

BackgroundIn stereotactic radiosurgery, sharp beam edges have clear advantages to spare normal tissues. In general, the dose gradient is a limiting factor in minimizing dose to nearby critical structures for clinical cases. Therefore the penumbral width should be diminished.MethodsA Varian Clinac 2100 linear accelerator equipped with in-house designed radiosurgical collimator was modeled using the EGSnrc/BEAMnrc Monte Carlo code and compared with the measurements. The 0.015 cm³ PinPoint chamber was used to measure the 6 MV photon beam characteristics and to validate Monte Carlo calculations. Additional to the standard (STD) linac, a flattening filter free (FFF) linac was simulated. Percent depth doses, beam profiles and output factors were calculated for small field sizes with diameter of 5, 10, 20 and 30 mm with DOSXYZnrc. The mean energy and photon fluence at the water surface were calculated with BEAMDP for both FFF linac and STD linacs.ResultsThe penumbra width (80%-20%) was decreased by 0.5, 0.3, 0.2 and 0.2 mm for field sizes of 5, 10, 20 and 30 mm respectively when removing the FF. The fluence of photons at the surface increased up to 3.6 times and the mean energy decreased by a factor of 0.69 when removing the FF. The penumbra width (80%-20%) decreased by 17% when a 2 MeV monoenergetic electron pencil beam incident on the target is used instead of 6.2 MeV.ConclusionsIt was found that the penumbra of small field sizes is decreased by removing the FF. Likewise using low megavoltage photons reduced the beam penumbra maintaining adequate penetration and skin sparing.     

Health-related quality of life in advanced non-small cell lung cancer: correlates and comparisons to normative data

LARSSON M., LJUNG L. & JOHANSSON B.B.K. (2012) European Journal of Cancer Care21, 642-649 Health-related quality of life in advanced non-small cell lung cancer: correlates and comparisons to normative data The aim was to describe self-reported health-related quality of life (HRQoL) in patients with advanced non-small cell lung cancer and to investigate the associations to stage of disease, age, gender, weight loss and performance status. Further, the study aimed to compare patients' HRQoL with that of the Swedish general population. Data on HRQoL were collected within a multi-centre randomised controlled trial. A total of 334 patients were included between 1998 and 2001. The European Organization for Research and Treatment of Cancer Quality of Life Questionnaire - Core Questionnaire (EORTC QLQ-C30) and Lung Cancer Questionnaire (EORTC QLQ-LC13) were used to assess HRQoL. HRQoL data for comparison with the Swedish population were derived from a random sample of the Swedish population. Patients reported a markedly impaired HRQoL compared to the normal population. There were statistically and clinically significant differences with regard to almost all QLQ-C30 functional and symptom scales. Global health status, physical functioning, role functioning and emotional functioning were markedly deteriorated. The most prominent symptoms were dyspnoea, fatigue, coughing, insomnia, appetite loss and pain. A low performance status, younger age, female gender and a more advanced disease were independently associated with a worse HRQoL. Additional studies are required to gain increased insight into this seriously ill group of patients and their need of supportive care.     

小细胞肺癌组织中VEGF和MVD的表达及意义

目的探讨小细胞肺癌(smallcelllungcancer,SCLC)组织中血管内皮生长因子(vascu-larendothelialgrowthfactor,VEGF)、微血管密度(microvesseldensity,MVD)的表达及其临床意义。方法应用SP法检测48例SCLC标本中的VEGF、MVD的含量,及其与临床生物学特性相关性。同时检测20例正常组织作对照分析。结果48例SCLC中VEGF阳性表达率为81%(39/48),MVD平均为52.82±15.34;VEGF阳性组MVD为54.71±11.12,阴性组为43.63±13.57,两组间差异有统计学意义,P=0.013。肿瘤直径≥3cm、区域淋巴结转移与MVD含量密切相关,P值分别为0.024和0.018;其中VEGF阳性率也高,但差异无统计学意义,P值分别为0.159和0.228。20例正常肺组织中VEGF阳性表达率为15%(3/20),MVD平均为18.23±6.92,均明显低于SCLC,P=0.000。结论SCLC组织中VEGF、MVD有高表达,可作为判断SCLC的生长、转移及预后的指标。