图像引导的放射治疗技术

胸腹部肿瘤因呼吸等生理运动处于不断运动的状态,影响成像、治疗计划和治疗过程的精确度。图像引导放疗（IGRT）技术有望解决运动肿瘤的精确治疗问题,它主要分为3个研究方向。其中,呼吸门控放疗开展较早,已经进入临床应用;集成放疗成像系统把定位和治疗设备合二为一,实现常规模拟定位、锥形束CT和实时成像等功能;射束同步放疗技术以四维CT成像技术为基础,控制动态多叶光栅使射束随着肿瘤的运动而不断运动,是最理想的放疗实现模式。     

影像技术在放射肿瘤学中的应用

自从1896年伦琴发现X射线,放射影像已经成为肿瘤诊断、分期、放疗定位、计划制定、实施照射和随访评价等必不可少的工具。随着20世纪中叶模拟机进入临床应用,通过X射线成像定位体内的骨性标记,从而进入了二维放疗计划的时代。在20世纪70年代早期,断层成像的发明使基于肿瘤或靶区体积的三维影像时代到来,通过CT或MRI显示肿瘤体积,这为三维适形放疗提供可能。近年来,CT技术不断发展,在三维基础上增加时间轴,称为四维CT,可以实现对运动肿瘤立体和动态的观察。该技术应用于放疗定位、计划制定及实施中,从而进入图象引导的四维放射治疗时代。同时,功能和分子影像技术也在快速发展,提示生物影像引导放射治疗时代已经来临。     

基于呼吸门控系统4D-CT模拟靶区的实验研究

0 引言 由呼吸和器官运动引起的肿瘤运动是放疗需要重点解决的问题之一[1],呼吸门控4D-CT技术能较好地解决呼吸和器官运动对放疗的影响[2-4],该技术通过检测患者体内外标记,将呼吸运动与肿瘤运动联系起来,把时间因素纳入到患者的CT扫描、重建、计划及治疗过程中,在特定时相对肿瘤实施放疗.     

磁共振放疗模拟定位技术应用现状与问题

放疗模拟定位是肿瘤放疗中的关键一步。目前放疗定位主要采用以CT为基础的模拟定位系统。与传统X线模拟机相比,CT实现了三维成像,提供了丰富的解剖信息和电子密度信息,是目前三维放疗技术实现的基础。然而,CT图像软组织分辨率低,特别是对前列腺、头颈部、盆腔、脊髓和其他软组织区域肿瘤(约占所有放疗病例30%~35%)显示不佳。对这些器官的肿瘤定位常常需要融合MRI或PET图像。由于患者在进行MRI或PET检查时体位与放疗科模拟定位CT时体位不一致(PET-CT除外),使得图像融合过程复杂,效率低且配准精度也低。而且各科室扫描侧重点不同,诊断科注重病变识别,而放疗定位需要空间位置准确性和摆位的重复性,因此诊断MRI并不适用于精确放疗定位。近年来,许多学者致力于MRI模拟定位技术研发。本文总结近年来MRI在放疗定位中的应用价值、MRI模拟定位实现方式、MRI成像序列设计和MRI模拟定位中存在的问题及解决办法,明确MRI模拟定位的未来研究方向。     

放射外科的最新进展

放射外科已有40年的历史，出现过伽玛刀和X刀两类医疗仪器。因伽玛刀治疗的范围局限于颅内病灶，而X刀精度较差，主要用于高分次、低剂量的常规放疗，所以在医学界并未引起广泛的注意。2001年射波刀开始用于临床，因其结构功能进了多种革新，如机器人照射系统的非等中心照射、自动调整位置的治疗床、高精度的自动摆位、治疗中频繁定位和射束随靶区位移而修正，以及可以治疗全身各部位的肿瘤，尤其是可以治疗随患者自然呼吸而移动的肿瘤，也就是四维治疗随呼吸而运动的肿瘤，包括原发性和转移性肺、肝、胰、肾和前列腺等肿瘤，预期对医学的贡献极大。无论从放射外科、手术或放疗的立场，都可认为射波刀是最新一代、最优质的局部病灶治疗方法。     

呼吸运动对调强放疗影响的实验研究

目的 :评价静态调强放疗治疗肺癌等运动幅度较大肿瘤的可行性。方法 :应用自行研制的运动体模系统模拟呼吸运动 ,测量不同运动幅度及不同运动方向对基于多叶光栅的静态调强放疗射束半影、剂量分布及绝对剂量的影响。结果 :靶区运动明显增加了射野在运动方向的半影 ,导致了低剂量区面积增大及高剂量区不确定性的增加 ,但70 %～ 90 %的等剂量线变化不显著。虽然不同情况下各测量点的剂量有不同程度的变化 ,但若将运动等不确定性因素考虑在内 ,多次测量后总体变化幅度均在允许的范围之内。结论 :靶区运动加宽了射束的半影 ,但在适当补偿运动等影响靶区确定的因素后 ,应用静态调强放疗治疗周期性运动的肿瘤是可行的     

超声成像在放疗中的临床应用

超声图像引导放疗（image guided radiation therapy,IGRT）是通过采集靶区二维超声断层图像或三维重建技术,辅助减小分次治疗的摆位误差、分次治疗间的靶区移位和变形以及同一分次中的靶区运动的技术。本文将系统回顾三维超声成像作为日常图像引导工具在放疗中的应用,并讨论这种成像技术在多种部位（如前列腺癌、妇科肿瘤和乳腺癌）中包括详细的扫描、采集技术及使用步骤的运用。最后,简要回顾放疗中用于靶区定位的其他成像技术,并比较这些成像技术之间的差异。     

实时呼吸监测在盆腔肿瘤放疗CT模拟定位中的应用

目的:探讨实时呼吸监测（RPM）技术在盆腔肿瘤放射治疗CT模拟定位中的应用价值。方法:选取我院2019年5月-2019年12月盆腔肿瘤放疗患者70例,其中实验组和对照组各35例。实验组患者CT模拟定位时采用RPM监测患者呼吸状态稳定后定位扫描,对照组常规方法定位扫描,利用锥形束CT采集患者放疗时的摆位误差信息同时记录当次放疗是否重复摆位,应用统计学方法对两组患者放疗时的摆位误差及重复摆位率数据进行分析。结果:两组在Y、Z 轴线性方向、X轴旋转方向误差及重复摆位率比较有统计学差异（P<0.05）,X轴线性方向及Y、Z轴旋转方向误差比较无统计学意义（P>0.05）。结论:盆腔肿瘤放疗患者在行CT模拟定位时应实时关注其身体状态变化,采用实时呼吸监测可有效的观测患者是否有紧张情绪或其他身体不适,避免了CT模拟定位时患者异常身体状态引起的放疗误差,可显著提高放射治疗精度及效率。     

呼吸运动对调强放疗影响的实验研究

目的：评价静态调强放疗治疗肺癌等运动幅度较大肿瘤的可行性。方法：应用自行研制的运动体模系统模拟呼吸运动，测量不同运动幅度及不同运动方向对基于多叶光栅的静态调强放疗射束半影、剂量分布及绝对剂量的影响。结果：靶区运动明显增加了射野在运动方向的半影，导致了低剂量区面积增大及高剂量区不确定性的增加，但70％～90％的等剂量线变化不显著。虽然不同情况下各测量点的剂量有不同程度的变化，但若将运动等不确定性因素考虑在内，多次测量后总体变化幅度均在允许的范围之内。结论：靶区运动加宽了射束的半影，但在适当补偿运动等影响靶区确定的因素后，应用静态调强放疗治疗周期性运动的肿瘤是可行的。     

MRI模拟定位物理实践指南北大核心CSCD

磁共振模拟定位是利用磁共振成像技术进行的放疗模拟定位,对实现肿瘤精准治疗有重要意义。本指南内容涵盖了放疗模拟定位实践工作的各项内容,包括磁共振模拟机的简介、安全要求和场地要求、验收调试、磁共振模拟定位工作流程以及日常质量控制。建议各单位参考本指南,制订本单位的放疗磁共振模拟定位实践规程,促进全国放疗磁共振模拟定位工作的标准化和同质化发展。     

La radiothérapie guidée par l’image (IGRT)

Image guided radiation therapy (IGRT) is a major technical innovation of radiotherapy. It allows locating the tumor under the linear accelerator just before the irradiation, by direct visualization (3D mode soft tissue) or indirect visualization (2D mode and radio-opaque markers). The technical implementation of IGRT is done by very different complex devices. The most common modality, because available in any new accelerator, is the cone beam CT. The main experiment of IGRT focuses on prostate cancer. Preliminary studies suggest the use of IGRT combined with IMRT should increase local control and decrease toxicity, especially rectal toxicity. In head and neck tumors, due to major deformation, a rigid registration is insufficient and replanning is necessary (adaptive radiotherapy). The onboard imaging delivers a specific dose, needed to be measured and taken into account, in order not to increase the risk of toxicity. Studies comparing different modalities of IGRT according to clinical and economic endpoints are ongoing; to better define the therapeutic indications.     

An overview of volumetric imaging technologies and their quality assurance for IGRT

Image-guided radiation therapy (IGRT) aims at frequent imaging in the treatment room during a course of radiotherapy, with decisions made on the basis of this information. The concept is not new, but recent developments and clinical implementations of IGRT drastically improved the quality of radiotherapy and broadened its possibilities as well as its indications. In general IGRT solutions can be classified in planar imaging, volumetric imaging using ionising radiation (kV- and MV- based CT) or non-radiographic techniques. This review will focus on volumetric imaging techniques applying ionising radiation with some comments on Quality Assurance (QA) specific for clinical implementation. By far the most important advantage of volumetric IGRT solutions is the ability to visualize soft tissue prior to treatment and defining the spatial relationship between target and organs at risk. A major challenge is imaging during treatment delivery. As some of these IGRT systems consist of peripheral equipment and others present fully integrated solutions, the QA requirements will differ considerably. It should be noted for instance that some systems correct for mechanical instabilities in the image reconstruction process whereas others aim at optimal mechanical stability, and the coincidence of imaging and treatment isocentre needs special attention. Some of the solutions that will be covered in detail are: (a) A dedicated CT-scanner inside the treatment room. (b) Peripheral systems mounted to the gantry of the treatment machine to acquire cone beam volumetric CT data (CBCT). Both kV-based solutions and MV-based solutions using EPIDs will be covered. (c) Integrated systems designed for both IGRT and treatment delivery. This overview will explain some of the technical features and clinical implementations of these technologies as well as providing an insight in the limitations and QA procedures required for each specific solution.     

螺旋断层放射治疗系统在中枢神经系统肿瘤中的应用

螺旋断层放射治疗系统（helical tomotherapy,HT）是利用一台6MV的医用直线加速器以螺旋CT旋转扫描方式,实现40 cm×160 cm范围的照射,是当今最先进的肿瘤放射治疗系统之一,集调强放射治疗（IMRT）、图像引导放射治疗（IGRT）、自适应放疗 (ART）和剂量引导放疗（DGRT）于一体。目前HT已初步应用于中枢神经系统良恶性肿瘤的治疗,照射精确、剂量分布均匀、能够有效保护危及器官,降低正常组织放疗毒性,应用前景广阔。现就HT在中枢神经系统肿瘤中的应用展开总结论述。     

影像引导放射治疗系统

影像引导放射治疗(IGRT)是近年来放射肿瘤学领域最先进的治疗技术。通过新型IGRT系统,将影像获取、治疗计划设计、CT模拟定位及加速器治疗完美地整合到一套放疗系统之中,以精确实施放射治疗。目前IGRT设备主要有传统直线加速器结合影像系统、断层放射治疗机和影像引导的立体定向治疗机。现就该类新技术及其临床应用作一综述。     

Radiothérapie guidée par l’image et partage des tâches avec les manipulateurs en électroradiologie : expérience de Clermont-Ferrand

The various image-guided radiotherapy techniques raise the question of how to achieve the control of patient positioning before irradiation session and sharing of tasks between radiation oncologists and radiotherapy technicians. We have put in place procedures and operating methods to make a partial delegation of tasks to radiotherapy technicians and secure the process in three situations: control by orthogonal kV imaging (kV-kV) of bony landmarks, control by kV-kV imaging of intraprostatic fiducial goldmarkers and control by cone beam CT (CBCT) imaging for prostate cancer. Significant medical overtime is required to control these three IGRT techniques. Because of their competence in imaging, these daily controls can be delegated to radiotherapy technicians. However, to secure the process, initial training and regular evaluation are essential. The analysis of the comparison of the use of kV/kV on bone structures allowed us to achieve a partial delegation of control to radiotherapy technicians. Controlling the positioning of the prostate through the use and automatic registration of fiducial goldmarkers allows better tracking of the prostate and can be easily delegated to radiotherapy technicians. The analysis of the use of daily cone beam CT for patients treated with intensity modulated irradiation is underway, and a comparison of practices between radiotherapy technicians and radiation oncologists is ongoing to know if a partial delegation of this control is possible.     

Image-guided radiotherapy: has it influenced patient outcomes?

Cancer control and toxicity outcomes are the mainstay of evidence-based medicine in radiation oncology. However, radiotherapy is an intricate therapy involving numerous processes that need to be executed appropriately in order for the therapy to be delivered successfully. The use of image-guided radiation therapy (IGRT), referring to imaging occurring in the radiation therapy room with per-patient adjustments, can increase the agreement between the planned and the actual dose delivered. However, the absence of direct evidence regarding the clinical benefit of IGRT has been a criticism. Here, we dissect the role of IGRT in the radiotherapy (RT) process and emphasize its role in improving the quality of the intervention. The literature is reviewed to collect evidence that supports that higher-quality dose delivery enabled by IGRT results in higher clinical control rates, reduced toxicity, and new treatment options for patients that previously were without viable options.     

Interest of positron-emission tomography and magnetic resonance imaging for radiotherapy planning and control

Computed tomography (CT) in the treatment position is currently indispensable for planning radiation therapy. Other imaging modalities, such as magnetic resonance imaging (MRI) and positron emission-tomography (PET), can be used to improve the definition of the tumour and/or healthy tissue but also to provide functional data of the target volume. Accurate image registration is essential for treatment planning, so MRI and PET scans should be registered at the planning CT scan. Hybrid PET/MRI scans with a hard plane can be used but pose the problem of the absence of CT scans. Finally, techniques for moving the patient on a rigid air-cushioned table allow PET/CT/MRI scans to be performed in the treatment position while limiting the patient's movements exist. At the same time, the advent of MRI–linear accelerator systems allows to redefine image-guided radiotherapy and to propose treatments with daily recalculation of the dose. The place of PET during treatment remains more confidential and currently only in research and prototype status. The same development of imaging during radiotherapy is underway in proton therapy.     

Les promesses de la radiothérapie. Focus sur les tumeurs pulmonaires

Radiotherapy is a key cancer treatment, which greatly modified its practice in recent years thanks to medical imaging and technical improvements. The systematic use of computed tomography (CT) for treatment planning, the imaging fusion/co-registration between CT/magnetic resonance imaging (MRI) or CT/positron emission tomography (PET) improve target identification/selection and delineation. New irradiation techniques such as image-guided radiotherapy (IGRT), stereotactic radiotherapy or hadron therapy offer a more diverse therapeutic armamentarium to patients together with lower toxicity. Radiotherapy, as well as medical oncology, tends to offer a personalized treatment to patients thanks to the IGRT, which takes into account the inter- or intra-fraction anatomic variations. IGRT leads to adaptive radiotherapy (ART) with a new planification in the treatment course in order to decrease toxicity and improve tumor control. The use of systemic therapies with radiations needs to be studied in order to improve efficiency without increasing toxicities from these multimodal approaches. Finally, radiotherapy advances were impacted by radiotherapy accidents like Epinal. They led to an increased quality control with the intensification of identity control, the emergence of in vivo dosimetry or the experience feedback committee in radiotherapy. We will illustrate through the example of lung cancer.     

Organ motion in image-guided radiotherapy: lessons from real-time tumor-tracking radiotherapy

External radiotherapy using imaging technology for patient setup is often called image-guided radiotherapy (IGRT). The most important problem to solve in IGRT is organ motion. Four-dimensional radiotherapy (4DRT), in which the accuracy of localization is improved – not only in space but also in time – in comparison to 3DRT, is required in IGRT. Real-time tumor-tracking radiotherapy (RTRT) has been shown to be feasible for performing 4DRT with the aid of a fiducial marker near the tumor. Lung, liver, prostate, spinal/paraspinal, gynecological, head and neck, esophagus, and pancreas tumors are now ready for dose escalation studies using RTRT.     

MRI/linac integration.

PURPOSE/OBJECTIVES: In radiotherapy the healthy tissue involvement still poses serious dose limitations. This results in sub-optimal tumour dose and complications. Daily image guided radiotherapy (IGRT) is the key development in radiation oncology to solve this problem. MRI yields superb soft-tissue visualization and provides several imaging modalities for identification of movements, function and physiology. Integrating MRI functionality with an accelerator can make these capacities available for high precision, real time IGRT. DESIGN AND RESULTS: The system being built at the University Medical Center Utrecht is a 1.5T MRI scanner, with diagnostic imaging functionality and quality, integrated with a 6MV radiotherapy accelerator. The realization of a prototype of this hybrid system is a joint effort between the Radiotherapy Department of the University of Utrecht, the Netherlands, Elekta, Crawley, U.K., and Philips Research, Hamburg, Germany. Basically, the design is a 1.5 T Philips Achieva MRI scanner with a Magnex closed bore magnet surrounded by a single energy (6 MV) Elekta accelerator. Monte Carlo simulations are used to investigate the radiation beam properties of the hybrid system, dosimetry equipment and for the construction of patient specific dose deposition kernels in the presence of a magnetic field. The latter are used to evaluate the IMRT capability of the integrated MRI linac. CONCLUSIONS: A prototype hybrid MRI/linac for on-line MRI guidance of radiotherapy (MRIgRT) is under construction. The aim of the system is to deliver the radiation dose with mm precision based on diagnostic quality MR images.