螺旋断层放疗在胸中下段食管癌治疗中对心脏功能保护的研究

【摘要】目的:对比胸中下段食管癌螺旋断层放疗和适形调强放疗心脏的剂量分布,分析螺旋断层放疗前后的心肌酶谱,评估螺旋断层放疗在食管癌治疗中对心脏功能的保护作用。方法:筛选37例胸中下段食管鳞癌患者,为每位患者制定适形调强放疗和螺旋断层放疗计划,比较两种放疗方式的计划靶区（PTV）、心脏的剂量学参数。同时在螺旋断层放疗前一周及一周后进行心肌酶谱检查,并对放疗心肌酶谱进行对比分析。结果:螺旋断层放疗的PTV与心脏最大剂量,心脏V20、V30、V40、V50、V60均明显低于适形调强放疗,差异有统计学意义（P<0.05）;两种放疗方式的PTV适形度指数差异有统计学意义（P<0.05）,而PTV均匀性指数、TOMO前后心肌酶谱差异无统计学意义（P>0.05）。结论:螺旋断层放疗在靶区剂量分布优于适形调强放疗的条件下,能显著降低心脏的最大剂量,并且引起的早期心肌损伤不明显,对心脏起到更好的保护作用。     

HI—ART螺旋断层治疗机多叶准直器机械性能测试

目的:测试螺旋断层加速器多叶准直器的机械性能.方法:分别对螺旋断层治疗机的铅门位置的准确性、铅门运动的对称性、多叶准直器的叶片位置和叶片平行性以及叶片的凸槽效应进行测试,将测试结果与厂家金标准进行比对.结果:由胶片分析得到铅门在Y方向相对于等中心的位置坐标yoffset=0.19mm.铅门中心最大偏差和平均偏差分别为0.07 mm、0.03 mm,铅门旋转偏移的测量结果是Y,方向铅门中心的位置偏差为-0.11 mm,由MVCT电离室探测器阵列测量X方向相对于等中心的位置偏差为0.12 mm.照射野中心相对于等中心的位置坐标cor=0.10 mm,叶片偏离运动方向的角度为0.19°.叶片凹凸槽效应在90%到112%之间.结论:螺旋断层治疗及的多叶准直器机械性能均满足厂家推荐标准,可以用于临床治疗.     

影像增强剂对脑瘤螺旋断层放疗剂量计算的影响

目的:研究影像增强剂对脑瘤螺旋断层放疗(HT)计划剂量计算的影响,探讨使用定位CT增强图像替代平扫图像用于靶区勾画和剂量计算的临床可行性。方法:收集30例脑瘤病例,所有病例均在增强图像上勾画靶区和危及器官轮廓,再把靶区和危及器官轮廓复制到平扫图像上。在HT计划系统中分别以增强图像和平扫图像设计两组放疗计划,比较两组靶区和危及器官的CT值、剂量分布和治疗时间。结果:两组图像的CT值在瘤区域(PGTV)处具有统计学差异(P0.05),其他组织CT值比较无统计学差异;计划靶区和危及器官的剂量学、治疗时间等参数的差异比较均无统计学差异(P0.05)。结论:影像增强剂对脑瘤HT计划剂量计算影响极小,脑瘤放疗中可以使用定位CT增强图像替代定位CT平扫图像用于靶区勾画和螺旋断层放疗计划剂量计算。     

乳腺癌螺旋断层放射治疗与调强放射治疗的剂量学研究与临床剂量实测比较

目的:利用螺旋断层放射治疗技术与传统医用直线加速器对乳腺癌放疗中重要正常组织与靶区剂量-体积参数进行剂量学比较。同时,在剂量学研究基础上进行临床实际吸收剂量测量验证各种技术间临床应用的优势与劣势。 方法:选取10例T1N0M0期乳腺癌保乳术后行乳腺靶区放射治疗病人（无锁骨上照射区域）,处方剂量为50 Gy/25次,利用螺旋断层放射治疗定角调强技术、螺旋断层放疗技术与医用直线加速器调强技术,比较乳腺癌靶区剂量和正常组织剂量的优劣。评估靶区剂量与适形度指数（CI）、均匀性指数（HI）和正常组织剂量-体积参数,进行剂量学比较。同时,利用热释光剂量仪在乳腺癌病人表皮进行实测剂量,比较3种技术处理由于病人呼吸运动对表面剂量的影响,及评估时间因素对治疗效率的影响。 结果:10例乳腺癌病人采用定角调强技术、螺旋断层放疗技术与医用直线加速器调强技术PTV HI分别为0.15±0.01、0.06±0.01和0.20±0.15（P<0.001）;CI分别为0.76±0.00、0.81±0.03和0.74±0.04（P>0.05）;心脏平均剂量分别为4.12±0.87、3.82±0.53、6.33±2.49 Gy（P<0.001）,左前降支最大剂量分别为20.38±5.66、13.34±3.78、34.56±4.12 Gy（P<0.001）,患侧肺组织平均剂量分别为6.78±1.33、7.22±2.34、12.76±2.10 Gy（P<0.001）。患者6个实测剂量点的吸收剂量3种技术比较有统计学意义（P<0.001）。 结论:从综合靶区覆盖、正常组织剂量-体积参数、剂量实测与治疗效率等方面比较,螺旋断层放射治疗的定角调强技术相对于其他两种技术而言有低剂量范围小、靶区覆盖佳、解决治疗中呼吸运动影响等优势,推荐使用该技术用于乳腺癌病人放射治疗。     

胰腺癌螺旋断层调强放疗剂量学分析

目的：分析胰腺癌螺旋断层调强放疗（HelicalTomotherapy,HT）靶区剂量和危及器官受量,给临床医生选择合适的照射剂量提供依据。方法：对13例进行螺旋断层调强放疗的胰腺癌病人靶区剂量分布和危及器官的进行回顾行分析,探讨剂量实施的合理性。结果95％和100％的处方剂量覆盖的临床靶区（CTV）体积分别平均为99．03％和95．69％．CTV适形指数（CI）和靶区剂量均匀指数（HI）分别平均为0．81±0．10和1．08±0．02。放疗计划中十二指肠的V30、V20、V10分别平均为11．91±6．46％、32．56±23．14％、62．49±22．57％,右肾的V20、V10分别平均为12．09±12．05％、35．82±2．96％,左肾的V30、V20和V10分别为2．05±1．80％、12．79±8．42％和29．56±16．56％,脊髓最大受量平均为28．02±2．96Gy,胃的V30、V20和V10平均受量为10．08±4．93％、20．28±8．51％和35．03±24．11％。结论：胰腺癌螺旋断层调强放疗在给予靶区根治剂量的同时,能有效地降低危及器官的高剂量区,并把危及器官的照射剂量限制在耐受剂量以下。     

用不同剂量率全身照射技术的临床应用

目的：探讨用直线加速器不同剂量率全身照射技术的可行性。方法：采用直线加速器8MV—X射线。不同剂量率分次全身照射方案对9例白血病患者进行了骨髓移植前的预处理照射，用瑞典Seanditronix公司生产的DPD-12通道快速测量系统及其应用软件进行实时剂量监测。结果：检测结果显示符合临床要求，白血病患者全部骨髓移植成功。结论：本方法既避免放射性肺炎的发生，又降低了机器的损耗。     

剂量率和准直器角度对二维电离室矩阵调强验证Gamma通过率的影响

目的：研究剂量率和准直器角度对二维电离室矩阵调强验证Gamma通过率的影响。方法：使用PTw二维电离室矩阵对2组36例测试病例进行验证。两组病例分别对应不同剂量率组和不同准直器角度组,比较不同的剂量率（100cGy／min-600Gy／min的整百剂量率）和准直器角度对3％、3mm标准Gamma分析的影响。结果：本研究中6档剂量率两两配对共计15对,配对t检验结果中,除了200和500这一对t=-3．68,P〈0．05,有统计学差异,其余14对配对t检验结果均为P〉0．05,无统计学差异;不同的准直器角度Gamma通过率配对t检验结果t=-15．582,P〈0．05,有统计学差异。结论：不同的剂量率对二维电离室矩阵调强验证Gamma通过率无明显影响,不同的准直器角度对二维电离室矩阵调强验证Gamma通过率有明显的影响．制订治疗计划时适当的调整准直器角度,使不同射野的准直器角度互不相同能够明显提高调强验证的通过率。     

螺旋断层放疗自适应技术的初步应用

目的：通过比较螺旋断层自适应计划与非自适应计划中危及器官的受照剂量体积,评估应用螺旋断层放疗减少周围正常组织受照体积的临床可行性。方法与材料：收集5例患者治疗过程中每完成5个分次剂量后在螺旋断层治疗机上采集的兆伏级CT（MVCT）图像并勾画肿瘤范围（GTV）并测量GTV的体积,评价GTV的体积变化。完成20个分次照射剂量后应用MVCT图像勾画缩减后的GTV并创建自适应计划,通过比较自适应计划与非自适应计划危及器官的体积剂量直方图（DVH）,评估自适应放疗的剂量学优势。结果：5例应用螺旋断层放疗自适应技术的病人的GTV在完成25个治疗分次后与治疗前比较均有明显的缩小（约为40%～60%）。三例肺癌患者接受20 Gy照射的同侧肺的体积平均减少了8.76%;两例盆腔患者接受40 Gy照射的小肠体积减少了1.48%;接受40 Gy照射的直肠体积减少了8.86%;接受45 Gy照射的膀胱体积减少了7.67%。而应用螺旋断层放疗系统实施自适应放疗技术平均只需要185.4min。结论：应用螺旋断层放疗的自适应技术减少周围正常组织的受照体积在临床上是可行的。     

三维适形放射治疗位置与剂量精度的验证

目的:验证三维适形放射治疗位置与剂量精度.方法:采用胶片法和电离室法,对所使用的治疗计划系统和加速器距离精度、靶中心位置精度及等中心吸收剂量进行实测验证.结果:治疗计划系统所显示图像的距离精度＜1%,靶中心位置精度＜2mm,等中心吸收剂量精度＜1%.结论:所验证的三维适形放疗位置与剂量精度符合临床要求,验证方法可行.     

鼻咽癌螺旋断层调强放疗中优化MVCT扫描范围的可行性

目的:探讨鼻咽癌螺旋断层调强放疗中两种应用兆伏级高能X线计算机体层摄影术(MVCT)扫描范围的引导方案的可行性。方法:选取行螺旋断层调强放疗的鼻咽癌患者20例,每例患者各扫描30次MVCT,15次扫描范围为鼻咽部靶区+颈部,15次为只有鼻咽部靶区,共获600组数据,两组进行配对t检验。结果:鼻咽部靶区+颈部的摆位误差结果在左右(X)、头脚(Y)、前后(Z)方向线性误差和绕此3个方向形成的旋转误差(U、V、W)分别为(-0.20±1.15)mm、(-0.01±1.60)mm、(0.02±0.83)mm、(-0.31±0.80)°、(0.27±0.80)°、(-0.06±0.58)°;鼻咽部靶区摆位误差结果分别为(-0.21±1.39)mm、(-0.13±1.85)mm、(-0.02±1.14)mm、(-0.05±0.89)°、(0.18±0.89)°、(-0.18±0.63)°。两组在上述6个方向上的比较,P值分别为0.92、0.19、0.59、0.00、0.11、0.02,结果显示X、Y、Z、V方向上P值大于0.05,无统计学意义;U、W方向上P值小于0.05,有统计学意义。结论:两种扫描范围在鼻咽癌螺旋断层调强放疗中线性误差无统计学意义,可以采用只扫描鼻咽部靶区的方式进行图像引导放疗,节约治疗时间和减少患者不必要的辐射。     

Determination of the initial beam parameters in Monte Carlo linac simulation

For Monte Carlo linac simulations and patient dose calculations, it is important to accurately determine the phase space parameters of the initial electron beam incident on the target. These parameters, such as mean energy and radial intensity distribution, have traditionally been determined by matching the calculated dose distributions with the measured dose distributions through a trial and error process. This process is very time consuming and requires a lot of Monte Carlo simulation experience and computational resources. In this paper, we propose an easy, efficient, and accurate method for the determination of the initial beam parameters. We hypothesize that (1) for one type of linacs, the geometry and material of major components of the treatment head are the same; the only difference is the phase space parameters of the initial electron beam incident on the target, and (2) most linacs belong to a limited number of linac types. For each type of linacs, Monte Carlo treatment planning system (MC-TPS) vendors simulate the treatment head and calculate the three-dimensional (3D) dose distribution in water phantom for a grid of initial beam energies and radii. The simulation results (phase space files and dose distribution files) are then stored in a data library. When a MC-TPS user tries to model their linac which belongs to the same type, a standard set of measured dose data is submitted and compared with the calculated dose distributions to determine the optimal combination of initial beam energy and radius. We have applied this method to the 6 MV beam of a Varian 21EX linac. The linac was simulated using EGSNRC/BEAM code and the dose in water phantom was calculated using EGSNRC/DOSXYZ. We have also studied issues related to the proposed method. Several common cost functions were tested for comparing measured and calculated dose distributions, including chi2, mean absolute error, dose difference at the penumbra edge point, slope of the dose difference of the lateral profile, and the newly proposed Kappaalpha factor (defined as the fraction of the voxels with absolute dose difference less than alpha%). It was found that the use of the slope of the lateral profile difference or the difference of the penumbra edge points may lead to inaccurate determination of the initial beam parameters. We also found that in general the cost function value is very sensitive to the simulation statistical uncertainty, and there is a tradeoff between uncertainty and specificity. Due to the existence of statistical uncertainty in simulated dose distributions, it is practically impossible to determine the best energy/radius combination; we have to accept a group of energy/radius combinations. We have also investigated the minimum required data set for accurate determination of the initial beam parameters. We found that the percent depth dose curves along or only a lateral profile at certain depth for a large field size is not sufficient and the minimum data set should include several lateral profiles at various depths as well as the central axis percent depth dose curve for a large field size.     

Reference dosimetry in a scanned pulsed proton beam using ionisation chambers and a Faraday cup

In order to give the correct dose to a patient, the monitor chamber for a proton scanning system has to be calibrated. As recombination of ion pairs occurs in the monitor chamber, the relation between the number of particles traversing it per time unit and the ionization chamber signal is not linear. A method developed for a scanned pulsed proton beam taking the nonlinear monitor signal into account is described. A vital part of the reference dosimetry procedure is to determine the absorbed dose under reference conditions, which is recommended to be done with an ionization chamber. For a scanned pulsed proton beam, the recombination in the ionization chamber is not negligible and the signal from the ionization chamber has to be corrected. In this work, it is shown that although the pulse length is comparable to the ion transit time the beam can be considered as continuously scanned if the applied high voltage is not too small. Also shown is that the two-voltage formula for a continuous beam is under some conditions applicable for a continuous scanned beam as well.     

The nth root percent depth dose method for calculating monitor units for irregularly shaped electron fields

This study outlines an improved method for calculating dose per monitor unit values for irregularly shaped electron fields using the nth root percent depth dose method. This method calculates the percent depth dose and output factors for an irregularly shaped electron field directly from the measured electron beam percent depth dose curves and output factors for circular fields. The percent depth dose curves and output factors for circular fields are normalized and measured at a fixed depth of maximum dose for a reference field, respectively. When compared with the sector integral lateral buildup ratio method, the percent depth dose data calculated using the nth root method accounts more accurately for the change in lateral scatter with decreasing field size. Therefore, it provides more accurate values of dose per monitor unit at different depths for all type of field shapes and beam energies. For beam energies in the range of 6-21 MeV, the differences between measured and calculated dose per monitor unit values, at different depths, were found to be within +/- 1.0% when the nth root percent depth dose method was used for calculation and 12.6% when the sector integral lateral buildup ratio method was used. The nth root percent depth dose method was tested and compared with the sector integral lateral buildup ratio method for ten clinically used irregularly shaped inserts (cutouts). For small irregularly shaped fields, a maximum difference of 2% was found between calculated dose per monitor unit values and measurements when the nth root percent depth dose method was used; this difference changed to 7% when comparisons were made between measurements and calculations based on the sector integral lateral buildup ration method. For large irregular fields this difference was found to be within 1.5% and 3.5%, respectively.     

Using a photon phase-space source for convolution/superposition dose calculations in radiation therapy

For a given linac design, the dosimetric characteristics of a photon beam are determined uniquely by the energy and radial distributions of the electron beam striking the x-ray target. However, in the usual commissioning of a beam from measured data, a large number of variables can be independently tuned, making it difficult to derive a unique and self-consistent beam model. For example, the measured dosimetric penumbra in water may be attributed in various proportions to the lateral secondary electron range, the focal spot size and the transmission through the tips of a non-divergent collimator; the head-scatter component in the tails of the transverse profiles may not be easy to resolve from phantom scatter and head leakage; and the head-scatter tails corresponding to a certain extra-focal source model may not agree self-consistently with in-air output factors measured on the central axis. To reduce the number of adjustable variables in beam modelling, we replace the focal and extra-focal sources with a single phase-space plane scored just above the highest adjustable collimator in a EGS/BEAM simulation of the linac. The phase-space plane is then used as photon source in a stochastic convolution/superposition dose engine. A photon sampled from the uncollimated phase-space plane is first propagated through an arbitrary collimator arrangement and then interacted in the simulation phantom. Energy deposition kernel rays are then randomly issued from the interaction points and dose is deposited along these rays. The electrons in the phase-space file are used to account for electron contamination. 6 MV and 18 MV photon beams from an Elekta SL linac are used as representative examples. Except for small corrections for monitor backscatter and collimator forward scatter for large field sizes (<0.5% with <20 x 20 cm2 field size), we found that the use of a single phase-space photon source provides accurate and self-consistent results for both relative and absolute dose calculations.     

A modified method of calculating the lateral build-up ratio for small electron fields

This note outlines an improved method of calculating dose per monitor unit values for small electron fields using Khan's lateral build-up ratio (LBR). This modified method obtains the LBR directly from the ratio of measured, surface normalized, electron beam percentage depth dose curves. The LBR calculated using this modified method more accurately accounts for the change in lateral scatter with decreasing field size. The LBR is used along with Khan's dose per monitor unit formula to calculate dose per monitor unit values for a set of small fields. These calculated dose per monitor unit values are compared to measured values to within 3.5% for all circular fields and electron energies examined. The modified method was further tested using a small triangular field. A maximum difference of 4.8% was found.     

A dose-per-pulse monitor for a dual-mode medical accelerator

On a radiotherapy accelerator, the dose monitoring system is the last level of protection between the patient and the extremely high dose rate which all accelerators are capable of producing. The risk of losing this level of protection is substantially reduced if two or more dose monitoring systems are used which are mechanically and electrically independent in design. This paper describes the installation of an independent radiation monitor in a dual-mode, computer-controlled accelerator with a moveable monitor chamber. The added device is fixed in the beam path, is capable of monitoring each beam pulse, and is capable of terminating irradiation within the pulse repetition period if any measured pulse is unacceptably high.     

The influence of lateral electronic disequilibrium on the radiation treatment planning for lung cancer irradiation

Using higher energy photons can obtain better target dose uniformity and skin sparing for treating deep lesions, but the effect of lacking lateral scattering in the low-density lung may degrade the target coverage. To analyze the influence of lateral electronic disequilibrium on the radiation treatment planning for lung cancer, three dimension conformal treatment (3D-CRT) plans of using 6 MV and 18 MV X-ray respectively for a lung cancer case have been worked out by using pencil beam algorithm and collapsed cone algorithm provided by Helax-TMS treatment planning system for the same radiation field arrangement for both energies. Dose volume histogram (DVH) in target and organs at risk (OARs) are used for comparison of different plans. The study shows that using pencil beam algorithm, the target DVH are similar for 6 MV and 18 MV plan. However, using collapsed cone algorithm that can make account of lateral electron scattering, the target is underdosed. The change is even more pronounced for 18 MV plan. The doses for lung and spinal cord are similar for these two energies and two algorithms. Therefore, for lung cancer, dose calculation algorithm should have the ability of handling accurately the effect of the tissue density heterogeneity. It is better to use the lower-energy photons (6 MV) than to use the higher-energy photons (18 MV).     

Intensity modulated radiation therapy using laser-accelerated protons: a Monte Carlo dosimetric study

In this paper we present Monte Carlo studies of intensity modulated radiation therapy using laser-accelerated proton beams. Laser-accelerated protons coming out of a solid high-density target have broad energy and angular spectra leading to dose distributions that cannot be directly used for therapeutic applications. Through the introduction of a spectrometer-like particle selection system that delivers small pencil beams of protons with desired energy spectra it is feasible to use laser-accelerated protons for intensity modulated radiotherapy. The method presented in this paper is a three-dimensional modulation in which the proton energy spectrum and intensity of each individual beamlet are modulated to yield a homogeneous dose in both the longitudinal and lateral directions. As an evaluation of the efficacy of this method, it has been applied to two prostate cases using a variety of beam arrangements. We have performed a comparison study between intensity modulated photon plans and those for laser-accelerated protons. For identical beam arrangements and the same optimization parameters, proton plans exhibit superior coverage of the target and sparing of neighbouring critical structures. Dose-volume histogram analysis of the resulting dose distributions shows up to 50% reduction of dose to the critical structures. As the number of fields is decreased, the proton modality exhibits a better preservation of the optimization requirements on the target and critical structures. It is shown that for a two-beam arrangement (parallel-opposed) it is possible to achieve both superior target coverage with 5% dose inhomogeneity within the target and excellent sparing of surrounding tissue.     

侧向电子失衡对肺部肿瘤放射治疗计划设计的影响

目的 :分析高能X射线通过低密度的肺组织时 ,侧向电子失衡对肺部肿瘤放射治疗计划的影响。方法 :用 6MV和 18MVX射线对一例肺癌进行三维适形治疗 (3D CRT)计划设计 ,并用Helax TMS计划系统提供的笔形束算法和筒串算法对两种能量下的布野方案相同的 3D CRT计划进行剂量计算 ,比较靶区及危及器官的剂量分布、DVH等指标。结果 :采用笔形束算法 6MV与 18MV计划的等剂量线和DVH相近 ,18MV计划的靶区剂量均匀性略优于 6MV计划 ;而当采用能进行电子侧向散射修正的筒串算法时 ,靶区的高剂量覆盖程度明显变差 ,18MV计划靶区剂量亏损更为显著 ,6MV计划高剂量覆盖靶区的程度优于 18MV计划 ;不同能量、算法下肺和脊髓的受量基本相同。结论 :对于肺部肿瘤 ,剂量计算应采用能够准确修正不均匀组织影响的算法 ,非调强放射治疗时最好使用 6MVX射线。     

Development of an optimization concept for arc-modulated cone beam therapy

In this paper, we propose an optimization concept for a rotation therapy technique which is referred to as arc-modulated cone beam therapy (AMCBT). The aim is a reduction of the treatment time while achieving a treatment plan quality equal to or better than that of IMRT. Therefore, the complete dose is delivered in one single gantry rotation and the beam is modulated by a multileaf collimator. The degrees of freedom are the field shapes and weights for a predefined number of beam directions. In the new optimization loop, the beam weights are determined by a gradient algorithm and the field shapes by a tabu search algorithm. We present treatment plans for AMCBT for two clinical cases. In comparison to step-and-shoot IMRT treatment plans, it was possible by AMCBT to achieve dose distributions with a better dose conformity to the target and a lower mean dose for the most relevant organ at risk. Furthermore, the number of applied monitor units was reduced for AMCBT in comparison to IMRT treatment plans.