Innovations in image-guided radiotherapy

The limited ability to control for the location of a tumour compromises the accuracy with which radiation can be delivered to tumour-bearing tissue. The resultant requirement for larger treatment volumes to accommodate target uncertainty restricts the radiation dose because more surrounding normal tissue is exposed. With image-guided radiotherapy (IGRT) these volumes can be optimized and tumoricidal doses can be delivered, achieving maximal tumour control with minimal complications. Moreover, with the ability of high-precision dose delivery and real-time knowledge of the target volume location, IGRT has initiated the exploration of new indications for radiotherapy, some of which were previously considered infeasible.     

Gating and tracking, 4D in thoracic tumours

The limited ability to control for a tumour's location compromises the accuracy with which radiation can be delivered to tumour-bearing tissue. The resultant requirement for larger treatment volumes to accommodate target uncertainty restricts the radiation dose because more surrounding normal tissue is exposed. With image-guided radiation therapy (IGRT), these volumes can be optimized and tumouricidal doses may be delivered, achieving maximum tumour control with minimal complications. Moreover, with the ability of high precision dose delivery and real-time knowledge of the target volume location, IGRT has initiated the exploration of new indications in radiotherapy such as hypofractionated radiotherapy (or stereotactic body radiotherapy), deliberate inhomogeneous dose distributions coping with tumour heterogeneity (dose painting by numbers and biologically conformal radiation therapy), and adaptive radiotherapy. In short: “individualized radiotherapy”. Tumour motion management, especially for thoracic tumours, is a particular problem in this context both for the delineation of tumours and organs at risk as well as during the actual treatment delivery. The latter will be covered in this paper with some examples based on the experience of the UZ Brussel. With the introduction of the NOVALIS system (BrainLAB, Feldkirchen, Germany) in 2000 and consecutive prototypes of the ExacTrac IGRT system, gradually a hypofractionation treatment protocol was introduced for the treatment of lung tumours and liver metastases evolving from motion-encompassing techniques towards respiratory-gated radiation therapy with audio-visual feedback and most recently dynamic tracking using the VERO system (BrainLAB, Feldkirchen, Germany). This evolution will be used to illustrate the recent developments in this particular field of research.     

Image-guided Adaptive Radiotherapy for Bladder Cancer

Technological advancement has facilitated patient-specific radiotherapy in bladder cancer. This has been made possible by developments in image-guided radiotherapy (IGRT). Particularly transformative has been the integration of volumetric imaging into the workflow. The ability to visualise the bladder target using cone beam computed tomography and magnetic resonance imaging initially assisted with determining the magnitude of inter- and intra-fraction target change. It has led to greater confidence in ascertaining true anatomy at each fraction. The increased certainty of dose delivered to the bladder has permitted the safe reduction of planning target volume margins. IGRT has therefore improved target coverage with a reduction in integral dose to the surrounding tissue. Use of IGRT to feed back into plan and dose delivery optimisation according to the anatomy of the day has enabled adaptive radiotherapy bladder solutions. Here we undertake a review of the stepwise developments underpinning IGRT and adaptive radiotherapy strategies for external beam bladder cancer radiotherapy. We present the evidence in accordance with the framework for systematic clinical evaluation of technical innovations in radiation oncology (R-IDEAL).     

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.     

Radiothérapie conformationnelle avec modulation d’intensité (RCMI) guidée par l’image : impact de l’augmentation du volume irradié à faible dose ?

Image-guided radiotherapy (IGRT) combined or not with intensity-modulated radiation therapy (IMRT) are new and very useful techniques. However, these new techniques are responsible of irradiation at low dose in large volumes. The control of alignment, realignment of the patient and target positioning in external beam radiotherapy are increasingly performed by radiological imaging devices. The management of this medical imaging depends on the practice of each radiotherapy centre. The physical doses due to the IGRT are however quantifiable and traceable. In one hand, these doses appear justified for a better targeting and could be considered negligible in the context of radiotherapy. On the other hand, the potential impact of these low doses should deserve the consideration of professionals. It appears important therefore to report and consider not only doses in target volumes and in “standard” organs at risk, but also the volume of all tissue receiving low doses of radiation. The recent development of IMRT launches the same issue concerning the effects of low doses of radiation. Indeed, IMRT increases the volume of healthy tissue exposed to radiation. At low dose (< 100 mGy), many parameters have to be considered for health risk estimations: the induction of genes and activation of proteins, bystander effect, radio-adaptation, the specific low-dose radio-hypersensitivity and individual radiation sensitivity. With the exception of the latter, the contribution of these parameters is generally protective in terms of carcinogenesis. An analysis of secondary cancers arising out of field appears to confirm such notion. The risk of secondary tumours is not well known in these conditions of treatment associating IMRT and IGRT. It is therefore recommended that the dose due to imaging during therapeutic irradiation be reported.     

Image guided radiotherapy for prostate cancer

The purpose of external beam radiotherapy is to sterilize malignant tumours and at the same time to avoid complications by radiation injury to the surrounding healthy tissues. Modern radiation techniques in recent years have allowed to safely escalate the dose by approximately 10% for the treatment of prostate cancer, resulting in a disease control that is nowadays comparable to surgery or permanent seed implant brachytherapy. Two recent technical developments have dramatically increased the precision of radiation dose delivery: conformal radiotherapy and image guided radiotherapy (IGRT). Conformal radiotherapy aims to shape the dose distribution to the shape of the target. At least equally important as conformality is the accurate spatial delivery of the conformal dose distribution to the target. Conventional patient positioning by skin drawings and lasers is an imprecise way to target the prostate within the pelvis. The need for adequate patient/target setup led in recent years to the development of a variety of solutions. They bear in common that setup is no longer guided by skin marks but by some imaging modality. An ideal IGRT system would allow for daily prostate imaging without possible introduction of errors due to image-acquisition itself, do so within a reasonable time frame, without the necessity for implanted radio-opaque markers and preferentially without exposing the patient to radiation. A solution that combines all these features is inexistent so far.     

放射物理学及分子放射生物学在临床放疗实践中的应用和未来发展

最近几年,放射物理学和分子放射生物学的进步促进了放射肿瘤学的显著发展.目前,我们从常规的二维放疗到三维适形放疗,已进入了调强放疗(intensity-modulated radiotherapy,IMRT)和影像引导放疗(image-guided radiotherapy,IGRT)的时代.IMRT/IGRT可对肿瘤组织进行适形治疗,对正常组织适形地避免照射,从而改善肿瘤控制并减少治疗相关的放射损伤.目前无框架立体定向放射手术(stereotactic radiosurgery,SRS)和立体定向体部放疗(stereotactic body radiotherapy,SBRT)已进入临床应用,这为放射肿瘤临床提供了更多的治疗选择.随着影像引导技术的进步,近距离放疗得到了发展,尤其是应用于早期前列腺癌,获得了非常满意的长期疗效.带电粒子治疗,包括质子疗法是新开发的充满前景的领域.放疗与传统化疗、激素疗法、新的靶向治疗和基因疗法联合使用为克服放疗抗拒、改善放疗指数提供了更好的局部-区域和全身癌症控制效果.最近进行的一项关于头颈部癌的随机临床试验表明,与单纯放疗相比,放疗联合靶向治疗可以提高患者生存率,而在功能或分子影像学方面取得的进步为提高人们对肿瘤靶区的认识提供了新的机会(例如乏氧区),并可进行对应放射剂量的调强治疗.在放疗中整合PET/CT可在治疗计划测定中有助于进行靶区勾画和对放疗反应的评估.放射抗拒相关的肿瘤干细胞、基因表达图谱分析以及毫微秒技术也是新进展的领域,随着个体化用药的发展,正在作进一步研究.     

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.     

Techniques de radiothérapie guidée par l’image (IGRT)

In recent years, the new irradiation techniques as the conformal 3D radiation therapy and the intensity modulated radiation therapy (IMRT) have been strongly correlated with the technological developments. These techniques have heightened the necessity of a thorough localization and precise definition of the volumes of interest. In response to this challenge, new technologies known as image-guided radiation therapy (IGRT) have been developed and can be used in two of the main steps in external beam radiation therapy: 1) treatment preparation by determining target volume; and 2) treatment delivery by positioning the patient and localizing the target volume. Inthis paper, we focus on different IGRT techniques used in the second step: X-ray imaging (kV or MV), such as the ExacTrac® system and Cyberknife® imaging system, conventional in-room computed tomography (CT), cone beam computed tomography (CBCT), and non-ionizing imaging techniques, such as the detection of magnetic fiducials and tracking the surface of patients using video imaging.     

The Pivotal Role of the Therapeutic Radiographer/Radiation Therapist in Image-guided Radiotherapy Research and Development

The ability to personalise radiotherapy to fit the individual patient and their diagnosis has been realised through technological advancements. There is now more opportunity to utilise these technologies and deliver precision radiotherapy for more patients. Image-guided radiotherapy (IGRT) has enabled users to safely and accurately plan, treat and verify complex cases; and deliver a high dose to the target volume, while minimising dose to normal tissue. Rapid changes in IGRT have required a multidisciplinary team (MDT) approach, carefully deciding optimum protocols to achieve clinical benefit. Therapeutic radiographer/radiation therapists (RTTs) play a pivotal role in this MDT. There is already a great deal of evidence that illustrates the contribution of RTTs in IGRT development; implementation; quality assurance; and maintaining training and competency programmes. Often this has required the RTT to undertake additional roles and responsibilities. These publications show how the profession has evolved, expanding the scope of practice. There are now more opportunities for RTT-led IGRT research. This is not only undertaken in the more traditional aspects of practice, but in recent times, more RTTs are becoming involved in imaging biomarkers research and radiomic analysis. The aim of this overview is to describe the RTT contribution to the ongoing development of IGRT and to showcase some of the profession's involvement in IGRT research.     

Technical Radiotherapy Advances – The Role of Magnetic Resonance Imaging-Guided Radiation in the Delivery of Hypofractionation

Safe delivery of hypofractionated radiotherapy requires high levels of accuracy due to the high doses of radiation delivered per fraction. Magnetic resonance guided radiotherapy (MRgRT) represents a new treatment paradigm which allows improved visualisation of targets and organs at risk, alongside the capability to adapt the treatment plan in real time prior to treatment delivery. There are challenges to delivering hypofractionated radiotherapy with conventional image-guided radiotherapy (IGRT) techniques and MRgRT may help to improve accuracy in radiation delivery in a number of clinical and anatomical scenarios.Specifically, there is an emerging role of MRgRT in delivering stereotactic body radiotherapy (SBRT) for locally advanced pancreatic cancer (LAPC) due to the superior soft tissue contrast provided by Magnetic Resonance Imaging combined with the ability to accommodate variation in anatomical appearances during treatment delivery. Reported data on the use of MRgRT in LAPC and it's role in enabling dose escalation are discussed in this article.There are further potential benefits to the use of MRgRT, for example the use of functional imaging during treatment delivery and generation of synthetic computed tomography, which have previously been impractical or unachievable. The overall aim of this article is to demonstrate the utility of MRgRT in facilitating safe delivery of hypofractionated radiotherapy and to highlight ways in which it may help to overcome challenges posed by current IGRT techniques.     

Partage des tâches avec les manipulateurs en électroradiologie pour la radiothérapie guidée par l’image

The development of accelerators with on-board imaging systems now allows better target volumes reset at the time of irradiation (image-guided radiotherapy [IGRT]). However, these technological advances in the control of repositioning led to a multiplication of tasks for each actor in radiotherapy and increase the time available for the treatment, whether for radiotherapy technicians or radiation oncologists. As there is currently no explicit regulatory framework governing the use of IGRT, some institutional experiments show that a transfer is possible between radiation oncologists and radiotherapy technicians for on-line verification of image positioning. Initial training for every technical and drafting procedures within institutions will improve audit quality by reducing interindividual variability.     

Image-guided radiotherapy]

Recent advances in radiation oncology are based on improvement in dose distribution thanks to IMRT and improvement in target definition through new diagnostic imaging such as spectroscopic or functional MRI or PET. However, anatomic variations may occur during treatment decreasing the benefit of such optimization. Image-guided radiotherapy reduces geometric uncertainties occurring during treatment and therefore should reduce dose delivered to healthy tissues and enable dose escalation to enhance tumour control. However, IGRT experience is still limited, while a wide panel of IGRT modalities is available. A strong quality control is required for safety and proper evaluation of the clinical benefit of IGRT combined or not with IMRT.     

IGRT: Bildgesteuerte Strahlentherapie

In most clinical situations, the purpose of radiotherapy is to apply high doses to the target volume as well as the protection of organs at risk from the side effects of radiation. For biological reasons, radiation is usually administered as a fractionated therapy, which requires reproducibly precise immobilisation of the patient and positioning of the radiation isocenter in the correct location in relation to tumor geometry before each treatment. This allows a maximum reduction in the “safety margin” around the target volume. Positioning for extracranial regions is problematic because of the movement of the tumor in relation to bony structures, e.g. due to breathing or organ filling. This uncertainty leads to difficulties in establishing high precision techniques such as intensity modulated radiation therapy in the extracranial regions. This overview discusses image guided radiotherapy (IGRT) techniques. Immobilisation strategies (breath holding, gating) and position verification techniques based on 2D image-guidance (port films, EPID), 2D–3D guidance (bidirectional EPID localization in combination with implanted fiducial markers and optional supplementary infrared positioning) as well true 3D image guidance possibilities such as ultrasound-based positioning systems and in-room CTs are discussed.     

Radiothérapie guidée par l’image des cancers prostatiques : concepts et implications

Intensity modulated radiotherapy (IMRT) and image-guided radiotherapy (IGRT) are technological developments, which when applied in a model of prostate cancer, led to a significant reduction in the toxicity and digestive and urinary sequelae of 3D conformational radiotherapy. The major clinical benefits of these techniques with regard to reduced digestive and urinary toxicity are unequivocal since very few sequelae have been reported at 10 years (2% of grade 2 and 1% of grade 3 digestive toxicity; 11% of grade 2 and 5% of grade 3 urinary toxicity). Even when these two techniques are combined, IG–IMRT significantly diminishes late genitourinary toxicity. In the absence of adaptive radiotherapy, there are many IGRT protocols and repositioning techniques, and every step in the IGRT process must be carried out with extreme rigor: installing the patient and contention system, repositioning technique with or without fiduciary markers, type of repositioning imaging, definition of margins inherent in each technique (prostate, seminal vesicles and/or pelvic lymph nodes), frequency of repositioning during treatment, dietary constraints with or without rectal lavage. For these reasons, every centre that performs IGRT must carefully and rigorously assess the uncertainties of repositioning linked to the IGRT technique. In this review, we analyzed data from the literature based on dosimetric studies and the proven clinical impact in order to answer the different questions asked by radiation oncologists at every step of the IGRT process for cancer of the prostate. Recommendations are made for the repositioning protocols according to the most widely used repositioning techniques: fiduciary markers or soft tissues, kV-CBCT or MV-CBCT, 3D ultrasonography.     

图像引导放射治疗的临床应用

图像引导放射治疗(IGRT)是继三维适形放疗(3DCRT)和调强适形放疗(IMRT)之后,又一新的放疗技术,是提高放射治疗精度、保证与控制放疗质量的重要手段.这一技术发展快,普及快,有很强的治疗优势.     

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。     

Image-Guided Radiotherapy for Pelvic Cancers: A Review of Current Evidence and Clinical Utilisation

The meticulous selection and utilisation of image-guided radiotherapy (IGRT) are essential for optimal radiotherapy treatment delivery when using highly conformal treatment techniques in pelvic radiotherapy. Pelvic IGRT has several general IGRT issues to consider (such as choice of match strategy, prioritisation between multiple treatment targets and margin estimates) as well as issues specific to pelvic radiotherapy, in particular large inter-fraction organ variation. A range of interventions, including adaptive treatment strategies, have been developed to address these challenges. This review covers general considerations for the clinical implementation of pelvic IGRT in routine practice and provides an overview of current knowledge regarding pelvic inter-fraction organ motion. Published IGRT evidence for each of the major tumour sites (gynaecological, prostate, bladder, rectal and anal cancer) is summarised, as are state-of-the-art adaptive approaches. General recommendations for the implementation of an institutional pelvic IGRT strategy include.•Ensuring consistency between treatment intent and the IGRT approach utilised.•Ensuring minimum national and international IGRT guidance is followed while considering the benefit of daily volumetric IGRT.•Ensuring the appropriate allied health professionals (namely therapy radiographers/radiation therapists) lead on undertaking IGRT.•Ensuring the IGRT workflow procedure is clear and includes an escalation process for difficult set-ups.•Ensuring a robust IGRT service is in place before implementing advanced adaptive approaches.