Pinnacle计划系统脚本在医用直线加速器碰撞防护中的应用

目的:探讨在放疗计划设计阶段使用Pinnacle计划系统脚本程序，实现医用直线加速器旋转治疗时的碰撞检测功能，提高放疗计划设计的可执行性，保证治疗安全。方法:根据C型臂加速器的治疗机头、病人CT图像和治疗床的几何结构信息，确定机架旋转过程中距离治疗中心的最小安全距离。在Pinnacle计划系统中设计脚本程序，根据当前放疗计划射野治疗中心的位置，模拟生成加速器机头旋转过程中临界安全位置的运动轨迹，并以辅助感兴趣区（ROI）的形式导入计划系统，在计划系统的CT和ROI的叠加影像上判断加速器机头与治疗床、病人是否存在碰撞风险。结果:脚本程序可根据当前病人摆位、治疗中心位置等计划设置参数，自动生成辅助ROI结构并导回计划系统，在CT图像的横断面上辅助ROI轨迹为圆形结构。计划设计时，只需一次鼠标点击，即可快速（约2 s）生成辅助ROI。在CT与ROI的叠加图像上可以逐层清楚直观地判断当前计划参数是否存在碰撞风险，避免计划实际执行时才发现会碰撞。结论:在Pinnacle 计划系统上实现加速器机头的碰撞检测具有临床可行性，使用本方法在计划设计阶段可及时判断放疗计划是否存在碰撞风险，避免重复计划延误治疗时间，保证治疗安全。     

Clearance assurance for stereotactic radiosurgery and radiotherapy

The nature of stereotactic radiotherapy (SRT)/radiosurgery (SRS) requires the use of oblique non-coplanar beams to avoid critical structures and maximize target coverage. These beams are delivered via a combination of gantry, collimator, and couch rotations. Such beam orientations could result in the gantry colliding with the patient or couch. The outcome can be patient injury, damaged equipment, and unrealized treatment. Our objective in this work was to create a treatment planning tool that utilizes each unique patient geometry to quantify clearance for stereotactic beams. Emphasis was placed on developing a general platform that can completely, yet easily, define any user system. Gantry components were described by providing component dimensions to software that generates thousands of surface points. Table components were described as a combination of boxes and measured surface points. During the treatment planning process isocenter coordinates, patient dimensions and beam orientation were specified. Gantry components were then transformed into the table reference frame. The shortest distance between the gantry and patient or couch was computed and compared to a safety margin. This clearance assurance algorithm was developed in response to the need to reduce patient setup time, and to increase the range of potentially useful beams. The software was verified by measuring minimum gantry-table distances at multiple beam orientations and comparing to calculations. Differences between calculated and measured clearances were on the order of 1 cm. The software enabled the safe delivery of noncoplanar oblique beams that are difficult to visualize. The software was used successfully to assure clearance for 50 patients (366 beams). This useful clinical tool became an integral part of the stereotactic quality assurance protocol at St Luke's-Roosevelt Hospital Center.     

Dose distributions in dynamic stereotactic radiosurgery

A treatment planning technique for calculation of dose distributions in dynamic stereotactic "radiosurgery" with a 10-MV isocentrically mounted linear accelerator is presented. The treatment planning for dynamic radiosurgery is a three-dimensional problem, since during treatment both the gantry and the couch rotate simultaneously, the gantry from 30 degrees to 330 degrees and the couch from 75 degrees to - 75 degrees. The patient surface and anatomical information is obtained from a family of computed tomography or magnetic resonance scans, and a stereotactic frame is used for target localization, treatment setup, and patient immobilization during the treatment. The dose calculational algorithm follows the gantry and couch rotation in an incremental fashion, and relies on measured stationary beam central axis percentage depth doses and dose profiles to calculate the normalized tissue-maximum-ratio distributions over a matrix of points defined on one of three orthogonal planes (transverse, sagittal, or coronal). The dose calculation algorithm is discussed in detail and calculated dose distributions for single plane and dynamic radiosurgery compared with measured data.     

A method of beam-couch intersection detection

At the time of treatment planning it would be useful to know whether part of the treatment beam passes through the patient/couch support assembly before it passes through the patient. In the previous work of Yorke, the range of gantry angles leading to beam-couch intersection was found as a function of couch translation for symmetric field sizes and for zero couch rotation. Yorke's method has been extended to include couch rotation, dual independent jaws, and multi-leaf collimator (MLC) field shapes. In addition, the new method is also applicable in the situation of the couch top located above the isocenter. For a clinically treatable, 20 x 20 cm field configuration in a linac, the range of gantry angles leading to beam-couch intersection are different by 6.7 degrees for a couch rotation angle of 25 degrees when compared to no couch rotation. The new method agrees with data within the setup and measurement uncertainties for a variety of field sizes including an oval shaped MLC field, and various couch locations, couch, and collimator rotation angles.     

Feldkamp-based cone-beam reconstruction for gantry-tilted helical multislice CT

Depending on the clinical application, it is frequently necessary to tilt the gantry of an x-ray CT system with respect to the patient and couch. For single-slice fan-beam systems, tilting the gantry introduces no errors or artifacts. Most current systems, however, are helical multislice systems with up to 16 slices. The multislice helical reconstruction algorithms used to create CT images must be modified to account for tilting of the gantry. If they are not, the quality of reconstructed images will be poor with the presence of significant artifacts, such as smearing and double-imaging of anatomical structures. Current CT systems employ three primary types of reconstruction algorithms: helical fan-beam approximation, advanced single-slice rebinning, and Feldkamp-based algorithms. This paper presents a generalized helical cone-beam Feldkamp-based algorithm that is valid for both tilted and nontilted orientations of the gantry. Unlike some of the other algorithms, generalization of the Feldkamp algorithm to include gantry tilt is simple and straightforward with no significant increase in computational complexity. The effect of gantry tilt for helical Feldkamp reconstruction is to introduce a lateral shift in the isocenter of the reconstructed slice of interest, which is a function of the tilt, couch speed, and view angle. The lateral shift is easily calculated and incorporated into the helical Feldkamp backprojection algorithm. A tilt-generalized helical Feldkamp algorithm has been developed and incorporated into Aquilion 16-slice CT (Toshiba, Japan) scanners. This paper describes modifications necessary for the tilt generalization and its verification.     

Patient-specific planning for prevention of mechanical collisions during radiotherapy

A common unwanted difficulty in treatment planning, especially in non-coplanar radiotherapy set-ups, is the potential collision of the rotating gantry with the couch and/or the patient's body. A technique and computer program that detects these and signals avoidance of such beam directions is presented. The problem was approached using analytical geometry. The separate components within the treatment room have either been measured and modelled for an Elekta linear accelerator, or read out from a Pinnacle3 treatment planning system and are represented as an integer grid of points in three-dimensional (3D) space. The module is attached to the treatment planning system and can provide rejection or acceptance of unwanted beam directions in a plan. In contrast to previous work that has only used patient models, each individual patient's outlines are considered here in their actual treatment position inclusive of any immobilization device. The extremities of the patient superiorly and inferiorly to the scanned region are simulated by an expanded version of the RANDO phantom. In this way, 'potential' collisions can be detected in addition to the certain ones. Patient position is not a limiting factor for the accuracy of the collision detection anymore, as each set-up is always created around the isocentre. Maps of allowed and forbidden zones within the treatment suite have been created by running the code for all possible gantry and couch angles for three commonly arising cases: a head and neck plan utilizing a small stereotactic collimator, a prostate plan with multileaf collimators and an abdominal plan with the lead tray attached. In the last case, the 3D map permitted significantly fewer set-up combinations. Good agreement between prediction and experiment confirmed the capability of the program and introduces a promising add-on for treatment planning.     

Elekta Infinity直线加速器治疗床对放疗剂量的影响

目的:研究Elekta Infinity直线加速器治疗床在常用X射线能量下对放疗剂量的影响。方法:将圆柱体模体分别置于碳纤维主治疗床、延长板以及治疗床与延长板衔接处正中,旋转机架,分别让6和10 MV高能X射线穿过治疗床,利用指形电离室测量固体水中间的绝对剂量,得出不同角度下的剂量分布,并计算治疗床对X射线的衰减因子。结果:治疗床与延长板衔接处在120°和240°两个机架角处的剂量衰减因子在6和10 MV两种治疗模式下分别达到了36.02%和36.01%以及30.46%和30.63%,而当机架角为140°~220°时,衔接处与主治疗床的剂量衰减因子相近,在6与10 MV能量下的剂量衰减因子平均值及标准差分别为2.56%±0.49%和2.14%±0.39%以及2.55%±0.48%和1.95%±0.41%,机架角由180°增大或减小时两处的剂量衰减均呈上升趋势,二者均在120°和240°附近达到最大;6和10 MV两种能量下延长板在该角度区间的剂量衰减因子平均值及标准差分别为1.55%±0.24%和1.07%±0.25%,并在115°和245°附近达到最大值,剂量衰减因子分别为4.08%和3.97%以及3.20%和3.34%。结论:后斜野主体部分在主治疗床与衔接处对剂量的衰减低于3%,在延长板处对剂量的衰减小于2%,但在120°和240°附近以及115°和245°附近3处位置的剂量衰减会达到最大,需在计划系统中考虑床的影响;此外,主治疗床与延长板衔接处在120°和240°附近对剂量的衰减急剧增大,不适合作为治疗区域,在治疗病人时需注意避免将靶区移到该区域。     

Four-dimensional computed tomography: image formation and clinical protocol

Respiratory motion can introduce significant errors in radiotherapy. Conventional CT scans as commonly used for treatment planning can include severe motion artifacts that result from interplay effects between the advancing scan plane and object motion. To explicitly include organ/target motion in treatment planning and delivery, time-resolved CT data acquisition (4D Computed Tomography) is needed. 4DCT can be accomplished by oversampled CT data acquisition at each slice. During several CT tube rotations projection data are collected in axial cine mode for the duration of the patient's respiratory cycle (plus the time needed for a full CT gantry rotation). Multiple images are then reconstructed per slice that are evenly distributed over the acquisition time. Each of these images represents a different anatomical state during a respiratory cycle. After data acquisition at one couch position is completed, x rays are turned off and the couch advances to begin data acquisition again until full coverage of the scan length has been obtained. Concurrent to CT data acquisition the patient's abdominal surface motion is recorded in precise temporal correlation. To obtain CT volumes at different respiratory states, reconstructed images are sorted into different spatio-temporally coherent volumes based on respiratory phase as obtained from the patient's surface motion. During binning, phase tolerances are chosen to obtain complete volumetric information since images at different couch positions are reconstructed at different respiratory phases. We describe 4DCT image formation and associated experiments that characterize the properties of 4DCT. Residual motion artifacts remain due to partial projection effects. Temporal coherence within resorted 4DCT volumes is dominated by the number of reconstructed images per slice. The more images are reconstructed, the smaller phase tolerances can be for retrospective sorting. From phantom studies a precision of about 2.5 mm for quasiregular motion and typical respiratory periods could be concluded. A protocol for 4DCT scanning was evaluated and clinically implemented at the MGH. Patient data are presented to elucidate how additional patient specific parameters can impact 4DCT imaging.     

The effect of gantry angle on megavoltage photon beam attenuation by a carbon fiber couch insert

The use of rigid carbon fiber couch inserts in radiotherapy treatment couches is a well-established method of reducing patient set-up errors associated with couch sag. Several published studies have described such inserts as radiotranslucent with negligible attenuation of the radiation field. Most of these studies were conducted with the radiation field normally incident on the couch and there appears to be no evidence in the literature of the effect of the gantry angle on the extent of beam attenuation by the carbon fiber insert alone during external beam radiotherapy. In this study we examined the magnitude of this effect over a range of posterior oblique gantry angles using a cylindrical solid water phantom containing an ionization chamber placed isocentrically. It was found that a 6 MV photon beam, field size 10 x 5 cm, was attenuated significantly as the gantry angle approached the plane of the couch, from 2% at normal incidence and reaching 9% attenuation at angle of incidence 70 degrees. This could have serious implications regarding dose to the treatment volume for treatments requiring posterior oblique angles of incidence with a possible correction factor necessary in monitor unit calculations.     

Beam optics design of compact gantry for proton therapy

A new proton therapy facility for the treatment of deep-seated tumours is being assembled. The proton beam will be applied to the patient under computer control, using dynamic scanning of a focused proton pencil beam to produce a complete three-dimensional conformation of the dose to the target volume. The beam will be applied to the supine patient using a compact isocentric gantry for protons. By combining the scanning of the beam with the beam optics and by mounting the patient couch eccentrically on the gantry, the diameter of the rotating structure can be reduced to 4 m, which is the smallest diameter designed so far for a proton gantry. The paper describes the project especially from the point of view of the optics of the beam transport system of the gantry, including the beam line used to inject the beam into the gantry.     

ArcCheck探测螺旋断层放疗误差的敏感性

目的:针对螺旋断层放疗（HT）系统,分析ArcCheck验证患者计划通过率对治疗床运动速度误差、机架旋转周期误差、机架起始角度误差、多叶准直器叶片开启时间误差的敏感性。方法:选取9例行HT的鼻咽癌患者计划,由自编程序生成与原计划相对应的误差计划。应用点剂量及Gamma分析,计算得出上述误差的临床可检测误差值。结果:所有患者的原计划采用3%/2 mm、2%/1 mm标准时的平均Gamma通过率分别为97.49%±1.08%、73.38%±4.31%。应用3%/2 mm通过率标准时,可检测的最小误差分别为治疗床运动速度:-1.58%、1.38%（上下限阈值）,机器旋转周期:-1.68%、1.31%（上下限阈值）,机架起始角度误差:2.50°,多叶准直器叶片开启时间:1.62%。而应用2%/1 mm标准时,检测精度得到提升,可检测的最小误差分别为治疗床运动速度:-0.69%、1.27%,机器旋转周期:-0.69%、0.69%,机架起始角度误差:2.06°,多叶准直器叶片开启时间:0.52%。结论:ArcCheck与电离室测量点剂量联用与单独使用ArcCheck Gamma通过率相比并未表现出明显优势,ArcCheck可以检测出临床相关的照射误差,更为严格的Gamma通过率标准可以明显提高误差计划的检测精度。     

JX—100X刀系统安全联锁装置设计

介绍一种应用于Ｘ刀系统防止加速器机架旋转照射过程中与治疗床和病人发生碰撞的安全装置的设计方法，并详细给出了其安装调试步骤。该装置已成功应用于第一军医大学研制的ＪＸ－１００Ｘ刀系统。     

A patient rotator for stereotactic radiosurgery

A new technique for stereotactic radiosurgery by use of a patient rotator is described. Using the rotator with a small collimated beam of 6 MV x-rays, a small well-defined region of the brain can be irradiated to a high dose with rapid fall off of the dose outside the target volume. Since the linear accelerator gantry does not move during therapy the possibility of a collision between the gantry and the patient or stereotactic equipment is eliminated. The system is also independent of the rotational stability of the linear accelerator gantry axis and turntable axis. Dose distributions measured in a Lucite head phantom with film exhibited properties well suited for radiotherapy. Tests carried out to evaluate the ability to irradiate a selected target point within the brain with the rotator system showed a maximum positional error of 1.0 and 2.0 mm for angiography and CT localisation respectively.     

Setup verification in linac-based radiosurgery.

A semi-automatic technique for the direct setup alignment of radiosurgical circular fields from an isocentric linac to treatment room laser cross-hairs is described. Alignment is achieved by acquiring images of the treatment room positioning laser cross-hairs superimposed on the radiosurgical circular field image. An alignment algorithm calculates the center of the radiosurgical field image as well as the intersection of the laser cross-hairs. This determines any alignment deviations and the information is then used to translate the radiosurgical collimator to its correct aligned position. Two detectors, each being sensitive to the lasers and ionizing radiation, were used to acquire the radiation/laser images. The first detector consists of a 0.3-mm-thick layer of photoconducting a-Se deposited on a 1.5-mm-thick copper plate and the second is film. The algorithm and detector system can detect deviations with a precision of approximately 0.04 mm. A device with gyroscopic degrees of freedom was built in order to firmly hold the detector at any orientation perpendicular to the radiosurgical beam axis. This device was used in conjunction with our alignment algorithm to quantify the isocentric sphere relative to the treatment room lasers over all gantry and couch angles used in dynamic stereotactic radiosurgery.     

A novel method to correct for pitch and yaw patient setup errors in helical tomotherapy

An accurate means of determining and correcting for daily patient setup errors is important to the cancer outcome in radiotherapy. While many tools have been developed to detect setup errors, difficulty may arise in accurately adjusting the patient to account for the rotational error components. A novel, automated method to correct for rotational patient setup errors in helical tomotherapy is proposed for a treatment couch that is restricted to motion along translational axes. In tomotherapy, only a narrow superior/inferior section of the target receives a dose at any instant, thus rotations in the sagittal and coronal planes may be approximately corrected for by very slow continuous couch motion in a direction perpendicular to the scanning direction. Results from proof-of-principle tests indicate that the method improves the accuracy of treatment delivery, especially for long and narrow targets. Rotational corrections about an axis perpendicular to the transverse plane continue to be implemented easily in tomotherapy by adjustment of the initial gantry angle.     

Evaluation of mechanical precision and alignment uncertainties for an integrated CT/LINAC system

A new integrated CT/LINAC combination, in which the CT scanner is inside the radiation therapy treatment room and the same patient couch is used for CT scanning and treatment (after a 180-degree couch rotation), should allow for accurate correction of interfractional setup errors. The purpose of this study was to evaluate the sources of uncertainties, and to measure the overall precision of this system. The following sources of uncertainty were identified: (1) the patient couch position on the LINAC side after a rotation, (2) the patient couch position on the CT side after a rotation, (3) the patient couch position as indicated by its digital readout, (4) the difference in couch sag between the CT and LINAC positions, (5) the precision of the CT coordinates, (6) the identification of fiducial markers from CT images, (7) the alignment of contours with structures in the CT images, and (8) the alignment with setup lasers. The largest single uncertainties (one standard deviation or 1 SD) were found in couch position on the CT side after a rotation (0.5 mm in the RL direction) and the alignment of contours with the CT images (0.4 mm in the SI direction). All other sources of uncertainty are less than 0.3 mm (1 SD). The overall precision of two setup protocols was investigated in a controlled phantom study. A protocol that relies heavily on the mechanical integrity of the system, and assumes a fixed relationship between the LINAC isocenter and the CT images, gave a predicted precision (1 SD) of 0.6, 0.7, and 0.6 mm in the SI, RL and AP directions, respectively. The second protocol reduces reliance on the mechanical precision of the total system, particularly the patient couch, by using radio-opaque fiducial markers to transfer the isocenter information from the LINAC side to the CT images. This protocol gave a slightly improved predicted precision of 0.5, 0.4, and 0.4 mm in the SI, RL and AP directions, respectively. The distribution of phantom position after CT-based correction confirmed these results. Knowledge of the individual sources of uncertainty will allow alternative setup protocols to be evaluated in the future without the need for significant additional measurements.     

History of tomotherapy

Tomotherapy is the delivery of intensity modulated radiation therapy using rotational delivery of a fan beam in the manner of a CT scanner. In helical tomotherapy the couch and gantry are in continuous motion akin to a helical CT scanner. Helical tomotherapy is inherently capable of acquiring CT images of the patient in treatment position and using this information for image guidance. This review documents technological advancements of the field concentrating on the conceptual beginnings through to its first clinical implementation. The history of helical tomotherapy is also a story of technology migration from academic research to a university-industrial partnership, and finally to commercialization and widespread clinical use.     

Improvement in banding artefacts in four-dimensional computed tomography for radiotherapy planning

Respiratory-gated CT (RGCT) and four-dimensional CT (4DCT) scan techniques cover consecutive segments of the respiratory cycle. However, motion artefacts may occur in fast respiratory phases such as mid-inhalation and -exhalation. CT imaging involves the use of a number of x-ray tube positions for each couch position. We investigated the fundamental nature of motion artefacts using a constant-velocity moving phantom in motion in the CT plane or perpendicular to the CT plane, and in pigs to simulate a human model. Artefacts and movement distance were evaluated in a moving phantom and artificially ventilated pigs with a 256-multi-detector row CT (256MDCT). The phantom moved in the CT plane or perpendicular to the CT plane with a constant velocity. Backprojection used variable initial backprojection angles (IBAs). The phantom length for motion perpendicular to the CT plane was independent of IBA but was represented by phantom diameter plus the distance of movement per gantry rotation. In contrast, that for the motion in the CT plane was dependent on IBA, as represented by phantom diameter plus the distance of movement per rotation for IBA perpendicular to the phantom movement direction, and phantom diameter plus half the distance of movement per gantry rotation for other IBAs. Results for volumetric CT images with different IBAs showed the presence of banding artefacts. Similar findings were seen in artificially ventilated pigs. Motion artefacts are unavoidable in both conventional CT and 256MDCT. Banding artefacts will be improved if the same IBAs at each couch position are accounted for during image reconstruction. This improvement will be beneficial in respiratory gated and 4D radiation therapies.     

应用提高分辨率的MatriXX检测等中心偏移的方法简介

目的:以检测等中心在X方向的偏移示例,介绍使用提高分辨率之后的MatriXX检测等中心偏移的方法。方法:在确保MLC的leaf bank关于collimator中心轴旋转对称,且MatriXX中心与等中心的偏差已知的基础上,将gantry和collimator的角度都设为0°,治疗床向X正方向每移动1 mm测量1次5 cm×5 cm照射野100 MU的剂量分布曲线,共7次移动治疗床,测量8组数据,然后将这8组数据叠加为一组复合数据,得到gantry和collimator角度为0°、5 cm×5 cm照射野100 MU时MatriXX在X方向分辨率为1 mm的剂量分布曲线。同样的方法测量得到将gantry角度设为180°时相对应的剂量分布曲线,然后使用OmniPro I’mRT软件对比分析这两个profile,得出等中心在X方向的偏移值。结果:等中心的偏移值为1.8 mm。结论:提高分辨率之后的MatriXX能够检测出等中心的偏移值;等中心的偏移会导致病人接受剂量出现偏差,而这种偏差可以通过调整Elekta Synergy MLC的leaf bank关于gantry旋转中心轴对称和计划设计中设置collimator与couch角度为0°来克服;等中心的偏差使得gantry角度在90°和270°附近照射野的平面剂量偏差非常大。因此,不建议计划设计中设置gantry角度在90°和270°附近的照射野,也不建议选用MatriXX或者其他平面探测器做照射野gantry角度集中在90°和270°附近的病人计划验证。     

有无均整器模式下臂架与准直器不同角度条件下的剂量学比较

目的:探讨臂架或准直器角度的改变对均整（FF）与非均整（FFF）两种模式的射线剂量的影响。方法:选用Versa HD直线加速器配备的6 MV/10 MV光子束FF/FFF模式4档能量在设定好九点位置的10 cm×10 cm标准射野内进行实验。首先,借助IMF等中心夹具将Mapcheck2固定于治疗机机头,并用Mapcheck2测量相同臂架与准直器角度条件下4种光子束输出的平面剂量值;其次,用Mapcheck2测量在相同臂架角度、不同准直器角度与相同准直器角度、不同臂架角度两种条件下4种光子束的中心轴剂量值;最后,固定准直器为0°,设立两组臂架对穿射野（0°与180°,90°与270°）。拆除Mapcheck2,采用固体水和FC65-G电离室建立一个测量模体来测量4种光子束在两组等中心对穿野的剂量。运用SPSS统计软件对该实验收集到的数据进行对比分析。结果:在相同臂架与准直器角度条件下,4种光子束辐照9个点的平面剂量之间均存在明显统计学差异（P6 MV FF =0.020, P6 MV FFF=0.017, P10 MV FF =0.030, P10 MV FFF=0.016）;而不同臂架角度或不同准直器角度条件下,4种能量光子束的中心轴点剂量值均无统计学差异。在0°与180°的对穿野,4种能量光子束的输出剂量存在统计学差异（P6 MV FF =0.001, P6 MV FFF=0.002, P10 MV FF =0.003, P10 MV FFF=0.001）,而在90°与270°的对穿野无统计学差异。结论:Versa HD直线加速器拥有优良的机械等中心性能。在实际工作时,臂架和准直器的旋转,均不影响光子束的中心轴剂量的准确输出。在FF模式下,射线能量越高,受治疗床影响越小;FFF模式射线由于射线质软,能量越高,更易受到治疗床的衰减作用,在实际中应引起重视。