基于胶片测量方法研究金属植入物对放疗剂量分布的影响

目的:采用胶片剂量仪测量方法研究不同材质金属植入物对放疗剂量分布的影响。方法:应用西门子ARTISTE直线加速器6MV X线在VENUS-SPD模体中分别对钛合金内固定板及不锈钢钢板进行照射,采用美国ISP公司GAFCHROMIC EBT2胶片进行测量并采用Film QA Pro3.0胶片分析软件将测量结果与治疗计划系统计算结果进行比较和评估。结果:不锈钢板和钛合金板X方向离轴曲线胶片测量值与TPS计算值的最大剂量偏差分别为9.6%和6.6%,相同DTA和△D条件下,不锈钢板和钛合金板治疗计划计算与胶片剂量测量通量分布比较Gamma检验通过率分别为78.11%和81.07%。结论:不同材质金属植入物对放疗剂量分布存在明显影响,治疗计划系统不能精确计算和评估金属植入物的剂量分布,建议实际放射治疗中对金属植入物患者进行剂量分布修正。     

肺癌三维适形放疗和常规放疗的剂量分布比较分析

比较肺癌三维适形放疗和常规放疗的剂量分布.对40例首程放疗肺癌患者同时进行X线和CT模拟定位,每位患者设计3套治疗计划:即三维适形治疗计划、常规治疗计划和虚拟常规治疗计划,通过剂量-体积直方图(DVH)的分析来评价不同放疗方式对肿瘤的剂量分布和危及组织、器官的受照剂量差异.说明三维适形放疗能给予靶区均匀的剂量分布,并能有效地保护正常组织和器官.     

骨科金属内植物置入后中高频电疗的应用

背景:中高频电疗是临床疾病治疗常用的物理治疗方法,广泛应用于各科,特别是骨科康复治疗。但康复治疗学通常将"局部金属植入物"作为中高频电疗的禁忌证,所以骨科金属内植物置入后通常不能进行中高频电疗。目的:综述目前国内外对骨科金属植入物置入后中高频电疗的研究现状,阐明中高频电疗对骨科金属植入物置入后对组织恢复的促进作用以及热损伤,探究中高频电疗在骨科金属植入物置入后对组织产生的影响及临床应用。方法:由第一作者应用计算机检索Pub Med数据及CNKI数据库,在标题和摘要中以"中、高频电疗,金属植入物,热损伤"或"middle and high frequency electrotherapy,metal implant,heat damage"为检索词,纳入与中高频电疗在骨科金属植入物置入后应用的相关研究文章。排除重复及较陈旧的文献。共40篇文献符合标准,中文33篇,英文7篇。结果与结论:随着钛合金等新的植入物材料的发展,越来越多的基础和临床研究发现治疗剂量的中高频电疗能够促进组织愈合,消除肿胀,并缓解疼痛。但目前还有许多疑问未完全解释清楚,比如中高频电疗对金属植入物周围造成损伤的剂量、造成热损伤的类型、组织学改变等;如果采用不同涂层的钛合金植入物,是否能减少热损伤,这些都需要进一步研究。     

肺癌肺内肿瘤不同能量三维适形放疗的比较

目的:研究6 MV和15 MV X射线对肺癌肺内肿瘤三维适形放疗肿瘤组织、危及器官及正常组织剂量的影响。方法:选择11例肺癌肺内肿瘤患者,对每例患者分别采用6 MV和15 MV X射线进行三维适形放疗计划设计,同一患者的两个计划均使用相同的布野方案和剂量体积约束。比较两组计划的计划靶区、危及器官及正常组织的剂量分布。结果:6MV和15 MV两种能量X线三维适形放疗计划计划靶区的剂量分布、均匀性、适形度的差异无显著性意义(P>0.05),危及器官脊髓、食管、心脏,正常组织肺的剂量分布无显著性意义(P>0.05)。结论:肺癌肺内肿瘤6 MV、15 MV三维适形放疗剂量分布无明显差异,三维适形放疗能量用6 MV,不主张用15 MV。     

调强逆向治疗计划中使用简化剂量计算模型的影响及其改善方法

制定逆向放疗计划时往往使用计算效率较高的简化剂量计算模型来得到射束元剂量矩阵,但使用简化的剂量计算模型可能会对最终调强计划的质量产生一定的影响.我们研究了在制定调强计划时使用简化剂量计算模型得到射束元剂量分布对最终沉积剂量的影响及其改善方法.采用两个模拟实例,使用两种剂量计算模型:原射线剂量计算模型(不考虑散射线的影响)和微分卷积积分剂量计算模型(考虑散射线的影响).结果表明用原射线剂量计算模型得到射束元剂量矩阵作调强最优化,可能导致靶区边缘剂量欠缺的情况,采用给靶区加扩展区的方法和平移叠野法可以改善靶区边缘的剂量分布情况.     

CT图像金属伪影校正算法研究现状

计算机断层成像(CT)技术已经广泛应用于临床诊断,它的高分辨率人体解剖信息对很多疾病的诊断提供了很大的帮助.然而,在患者体内有金属植入物的情况下,CT图像中往往伴随着大量黑色带状或明亮的放射条纹状伪影,统称为金属伪影.金属伪影使临床疾病诊断变得不再可靠,在放射治疗中也会给剂量分布的计算带来误差.消除CT图像中金属伪影的研究具有重要意义,对目前主要的金属伪影消除算法进行了总结和讨论.     

影响调强放疗绝对剂量的主要因素及应对措施

目的:验证调强放射治疗的绝对剂量误差,探索影响调强放疗绝对剂量的因素及其应对措施.方法:将20例准备实施调强放疗病人的实际治疗计划,用标准水模体进行计划移植,生成验证计划并计算体模内电离室测量点的计划剂量,执行验证计划的照射,用电离室进行实际物理绝对剂量测量,计算实际测量剂量值和计划剂量值的百分相对误差.分析影响调强放疗绝对剂量误差的主要因素,采取相应改进措施,验证另80例调强放疗的绝对剂量,比较前20例与改进后80例调强放疗绝对剂量验证结果.结果:前20例调强放疗绝对剂量百分相对误差分布范围是-8.00%～5.00%,平均误差为-2.01%,标准差为3.55%.采取相应改进措施后,80例调强放疗绝对剂量百分相对误差全部在4.4%以内,分布范围缩小到-4.4%～2.5%,平均误差为-1.49%,比前20例平均误差下降25.9%,标准差为1.40%,比前20例下降60.6%.结论:分析影响调强放疗绝对剂量的因素,采取必要的应对措施,能够有效提高调强放射治疗绝对剂量的准确性.     

放射治疗计划软件中等剂量线跟踪技术

背景与目的:放射治疗需要最大限度地提高肿瘤的放射剂量并尽可能减少正常组织所受到的剂量,以达到最佳的放疗效果。在制定治疗计划过程中,等剂量线是评估剂量分布的最重要的指标,为获得病人断层内的等剂量线,需要计算病人体素的剂量,该工作计算量大,耗费时间长。本研究旨在得出一种快速的等剂量线分布跟踪算法,以满足临床上对病体内放射剂量分布进行评价的需要。方法:本文研究了基于二值图的轮廓跟踪技术,采用基于8邻域法的等剂量线跟踪算法,结合"边计算、边跟踪",实现了治疗计划软件中的等剂量线跟踪技术。结果:8邻域法可以减少轮廓跟踪过程中的搜索点,结合"边计算、边跟踪"的方法,减少了剂量计算的体素点数,大大提高等剂量线跟踪的速度。结论:试验表明,使用本研究所提出的等剂量跟踪技术,能够较快地获得等剂量线,完全符合临床应用的要求。     

摆位误差对脑立体定向放射治疗剂量分布的影响

目的:探讨摆位误差对脑立体定向放疗剂量分布的影响,指导改进定位方案。方法:随机选取10例脑立体定向放疗患者,借助XVI采集患者摆位后治疗前的锥形束CT(CBCT)和放疗后的CBCT,分别与计划CT配准,获得放疗前和放疗中的摆位误差。借助Xio计划系统,研究摆位误差对计划靶区(PTV)的适形度、平均剂量和最大剂量值的影响。结果:脑立体定向放疗前和放疗中的摆位误差分别为(3.40±1.14)和(0.36±0.12)mm。放疗前摆位误差使PTV的相对适形度由1.00±0.00降低为0.81±0.17(P=0.007,t=-3.494),使相对平均剂量改变了1.56%±1.15%(P=0.002,t=4.304)。放疗中摆位误差对PTV剂量分布的影响可忽略。结论:图像引导的无框架脑立体定向放射治疗在线修正摆位误差,可获得较高的几何和剂量测量精度。     

不同骨科植入物对放射治疗的影响

分析商用的不锈钢植入物、钛基合金植入物以及自制的碳纤维植入物在放射诊断中的影像学区别及对放射治疗剂量的影响,探讨碳纤维植入物在放射治疗方面的应用前景.把3种不同材质的骨科植入物通过手术先后植入同一只家猪的同一只后腿,用普通模拟定位机和CT模拟定位机观察不同材质的骨科植入物对影像的影响,进而利用放射治疗计划系统分析不同植...     

Investigation into dosimetric effect of a MAGNA-SITE tissue expander on post-mastectomy radiotherapy

It is increasingly common for radiotherapy departments to encounter high density objects in patients being planned for radiotherapy. Many cases, such as artificial hip prostheses, are well documented. In our cancer center we have recently come across a new type of implant--a McGhan Style 133 Tissue Expander--implanted in patients who have undergone a mastectomy and will in future have breast reconstruction. This type of implant contains a small rare earth magnet encased in a titanium body, which induces significant perturbations in the dose distribution. These perturbations have been measured using a p-type semiconductor diode. Attenuation of up to 30% of local dose has been observed for a single beam. However, in more realistic clinical situations using tangential parallel opposed beams, it is estimated that part of the planning target volume maybe be underdosed by approximately 10%. Comparisons have been made between measured attenuation and that calculated by a treatment planning system, which demonstrates inadequate modeling of the dose perturbation caused by the implant in this case.     

Correction factors for low perturbation in vivo diodes used in the determination of entrance doses in high energy photon beams

PURPOSE: Low perturbation diodes, with thin buildup caps, can be used to reduce perturbations to the delivered dose. The literature states that additional correction factors are required for low perturbation diodes, however, there are few reported studies into their use. This report measured the dose perturbations and correction factors for diodes with varying buildup cap thicknesses. METHODS AND MATERIALS: Scanditronix EDP15, EDD5, and EDD2 diodes were investigated. Dose perturbations and correction factors for field size, source-surface distance (SSD), obliquity, and wedge were measured in megavoltage photon beams. RESULTS: EDP15 produces a 6% dose perturbation. EDD5 produces a perturbation between 1% and 2%. EDD2 perturbation is negligible. The variation of correction factors for the full buildup EDP15 diode is small and consistent with the literature. The low perturbation diode EDD2 has large correction factors. The field size correction factor varies from 1.38 to 0.87 for 10 MV. The SSD correction factor varies from 0.92 to 1.09 for 10 MV. At the maximum angle measured, the obliquity correction factor is 0.73 for 10 MV. Intermediate results were observed for the EDD5 diode. CONCLUSIONS: It is expected that it will be very difficult to achieve accurate in vivo dosimetry using the EDD2 diode. The EDD5 diode may represent a reasonable compromise between EDD2 and the full buildup EDP15. The EDD5 dose perturbation is small and the correction factors are not as large as for EDD2, so accurate in vivo dosimetry may be possible as long as the obliquity is below 45 degrees.     

Photon dose perturbations due to small inhomogeneities

An apparatus capable of measuring small fractional changes in ionization current has been used to study the effect of small inhomogeneities on photon dose in water. Small ring-shaped inhomogeneities were introduced into a water phantom and measurements have been made for 4-, 6-, and 18-MV x-rays. The results show beyond the range of secondary electrons, the dose perturbation is basically a photon transport phenomenon which becomes less important as the beam energy increases; within the range of secondary electrons, dose perturbation also involves electron transport, which has a strong dependence on atomic number and could result in a substantially large effect on dose deposition.     

Dose perturbation induced by radiographic contrast inside brachytherapy balloon applicators

Phantom measurements and Monte Carlo calculations have been performed for the purpose of characterizing the dose perturbation caused by radiographic contrast inside the MammoSite breast brachytherapy applicator. Specifically, the dose perturbation is quantified as a heterogeneity correction factor (HCF) for various balloon radii and contrast concentration levels. The dose perturbation is larger for larger balloon radii and higher contrast concentrations. Based on a validated Monte Carlo simulation, the calculated HCF values are 0.99 for a 2 cm radius balloon and 0.98 for a 3 cm radius balloon at 6% contrast concentration levels, and 0.89 and 0.87 for 2 and 3 cm radius balloons, respectively, at 100% contrast concentrations. For a typical implanted balloon radius of 2.4 cm, the HCF values decrease from 0.99 at 6% contrast concentration to 0.90 at 100% contrast concentration. For balloons implanted in patients at our institution, the mean HCF is 0.99, corresponding to a dose reduction of approximately 1%. The contrast effect results in a systematic reduction in the delivered dose, therefore the minimal amount of radiographic contrast necessary should be used.     

Dose perturbations at interfaces in photon beams: annihilation radiation

A model is presented for estimating the contribution of annihilation radiation to the dose perturbation at interfaces between high and low atomic number materials. The contribution is small, but not negligible relative to the total interface dose perturbation. The maximum contribution occurs for photon beams of about 8 MeV in energy. For an 8-MeV beam passing first through lead, then through polystyrene, the annihilation radiation contribution to the interface dose perturbation is about 8%, at a copper/polystyrene interface, the contribution is about 7%, and at an aluminum/polystyrene interface, the contribution is about 3%.     

Dose perturbations due to contrast medium and air in mammosite treatment: an experimental and Monte Carlo study

In the management of early breast cancer, a partial breast irradiation technique called MammoSite (Proxima Therapeutic Inc., Alpharetta, GA) has been advocated in recent years. In MammoSite, a balloon implanted at the surgical cavity during tumor excision is filled with a radio-opaque solution, and radiation is delivered via a high dose rate brachytherapy source situated at the center of the balloon. Frequently air may be introduced during placement of the balloon and/or injection of the contrast solution into the balloon. The purpose of this work is to quantify as well as to understand dose perturbations due to the presence of a high-Z contrast medium and/or an air bubble with measurements and Monte Carlo calculations. In addition, the measured dose distribution is compared with that obtained from a commercial treatment planning system (Nucletron PLATO system). For a balloon diameter of 42 mm, the dose variation as a function of distance from the balloon surface is measured for various concentrations of a radio-opaque solution (in the range 5%-25% by volume) with a small volume parallel plate ion chamber and a micro-diode detector placed perpendicular to the balloon axis. Monte Carlo simulations are performed to provide a basic understanding of the interaction mechanism and the magnitude of dose perturbation at the interface near balloon surface. Our results show that the radio-opaque concentration produces dose perturbation up to 6%. The dose perturbation occurs mostly within the distances <1 mm from the balloon surface. The Plato system that does not include heterogeneity correction may be sufficient for dose planning at distances > or = 10 mm from the balloon surface for the iodine concentrations used in the MammoSite procedures. The dose enhancement effect near the balloon surface (<1 mm) due to the higher iodine concentration is not correctly predicted by the Plato system. The dose near the balloon surface may be increased by 0.5% per cm3 of air. Monte Carlo simulation suggests that the interface effect (enhanced dose near surface) is primarily due to Compton electrons of short range (<0.5 mm). For more accurate dosimetry in MammoSite delivery, the dose perturbation due to the presence of a radio-opaque contrast medium and air bubbles should be considered in a brachytherapy planning system.     

Transmission and dose perturbations with high-Z materials in clinical electron beams

High density and atomic number (Z) materials used in various prostheses, eye shielding, and beam modifiers produce dose enhancements on the backscatter side in electron beams and is well documented. However, on the transmission side the dose perturbation is given very little clinical importance, which is investigated in this study. A simple and accurate method for dose perturbation at metallic interfaces with soft tissues and transmission through these materials is required for all clinical electron beams. Measurements were taken with thin-window parallel plate ion chambers for various high-Z materials (Al, Ti, Cu, and Pb) on a Varian and a Siemens accelerator in the energy range of 5-20 MeV. The dose enhancement on both sides of the metallic sheet is due to increased electron fluence that is dependent on the beam energy and Z. On the transmission side, the magnitude of dose enhancement depends on the thickness of the high-Z material. With increasing thickness, dose perturbation reduces to the electron transmission. The thickness of material to reduce 100% (range of dose perturbation), 50% and 10% transmission is linear with the beam energy. The slope (mm/MeV) of the transmission curve varies exponentially with Z. A nonlinear regression expression (t=E[alpha+beta exp(-0.1Z)]) is derived to calculate the thickness at a given transmission, namely 100%, 50%, and 10% for electron energy, E, which is simple, accurate and well suited for a quick estimation in clinical use. Caution should be given to clinicians for the selection of thickness of high-Z materials when used to shield critical structures as small thickness increases dose significantly at interfaces.     

Patient dose measurements in photon fields by means of silicon semiconductor detectors

Semiconductor detectors based on p-type silicon and designed for in vivo measurement of entrance dose at the reference point from photon radiation fields, are described. To estimate the absorbed dose at the reference point from measurements with a thin detector, field-size dependent correction factors must be applied to the reading, as the shape of the dose buildup curve varies with field size. To decrease or avoid field-size dependent correction factors, the detector can be covered with a buildup cap. The presence of such a detector will cause perturbation of the radiation field. Therefore, the design of a detector, irrespective of its type, intended for patient dosimetry involves a compromise between minimizing the radiation field perturbation and minimizing field-size dependent correction factors. Detectors with three different buildup caps were designed to cover the energy range from cobalt-60 to 16-MV x rays. The three different detector types were investigated with respect to their signal dependence on field size, field perturbation, and directional dependence. A summary of radiation damage effects on sensitivity, and of sensitivity variation with temperature is also presented.     

Responses of cerebellar Purkinje cells to slip of a hand-held object.

1. Two monkeys were trained to grasp, lift, and hold a device between the thumb and forefinger for 1 s. The device was equipped with a position transducer and strain gauges that measured the horizontal grip force and the vertical lifting or load force. On selected blocks of 20-30 trials, a force-pulse perturbation was applied to the object during static holding to simulate object slip. The animals were required to resist this displacement by stiffening the joints of their wrists and fingers to obtain a fruit juice reward. Single cells in the hand representation area of the paravermal anterior lobe of the cerebellar cortex were recorded during perturbed and unperturbed holding. If conditions permitted, the cell discharge was also recorded during lifting of objects of various weights (15, 65, or 115 g) or different surface textures (sandpaper or polished metal), and when possible the cutaneous or proprioceptive fields of the neurons were characterized with the use of natural stimulation. 2. On perturbed trials, the force pulse was always applied to the manipulandum after it had been held stationary within the position window for 750 ms. The perturbation invariably elicited a reflexlike increase of electromyographic (EMG) activity in wrist and finger muscles, resulting in a time-locked increase in grip force that peaked at a latency between 50 and 100 ms. 3. The object-slip perturbation had a powerful effect on cerebellar cortical neurons at a mean latency of 45 +/- 14 (SD) ms. Reflexlike increases or decreases in simple spike discharge occurred in 55% (53/97) of unidentified cells and 49% (21/43) of Purkinje cells recorded in the anterior paravermal and lateral cerebellar cortex. 4. The perturbation failed to evoke complex spike responses from any of the Purkinje cells examined. All the perturbation-evoked activity changes involved modulation of the simple spike discharge. The perturbations stimulated the simple-spike receptive field of most Purkinje cells recorded here, which suggests that the short-latency unit responses were triggered by afferent stimulation. Only one Purkinje cell was found with a distinct complex-spike receptive field on the thumb, but this neuron did not respond to the perturbation. It appears that simple- and complex-spike to receptive fields are not always identical or even closely related. 5. The majority of Purkinje and unidentified neurons that responded to the perturbation had cutaneous receptive fields, although some had proprioceptive fields. Seventy-seven neurons were examined for peripheral receptive fields and were also tested with the perturbation.(ABSTRACT TRUNCATED AT 400 WORDS)