Developing Quality Assurance Tools For Proton Beam Therapy

现代癌症治疗主要是三种技术的结合：手术、化疗和放疗。放射疗法使用x射线束从许多不同的方向照射肿瘤。其效果是通过在肿瘤中放置尽可能多的辐射剂量来杀死癌症，同时尽量减少对周围区域的辐射剂量，以保留健康组织。质子治疗是一种更精确的放射治疗形式，比传统的x射线放射治疗有显著的好处。质子失去能量，因此将它们的剂量储存在体内更小的区域，使治疗更加精确：这导致更有效的癌症治疗，减少癌症复发的机会。这对于治疗头部、颈部和中枢神经系统的深层肿瘤尤其重要，特别是对于身体仍在发育、特别容易受到长期辐射损害的儿童。质子治疗的优势，加上设备成本的降低，导致了全世界对质子治疗的兴趣激增：现在有超过20个中心，这一数字将在未来十年每三年翻一番。英国目前正在建造两个全尺寸的质子治疗中心，分别位于伦敦的大学学院医院和曼彻斯特的克里斯蒂医院，由英国国家医疗服务体系资助。这将为更广泛的癌症提供治疗，使更多的患者能够在离家更近的地方接受治疗。治疗这些癌症需要比传统放射治疗系统复杂得多的机器。质子被粒子加速器加速到适合治疗的能量：一旦光束离开加速器，它就必须通过一系列转向和聚焦磁铁被输送到几米外的治疗室。当质子束到达治疗室时，它必须通过一个龙门输送到正确的地方。质子治疗架是巨大的——超过3层楼高，重达100多吨——必须围绕病人旋转，以毫米级的精度从任何角度输送光束。为了确保使用如此复杂的机械安全进行治疗，每天在治疗开始前都要进行一系列质量保证（QA）程序。大部分时间都花在验证质子束行进的正确深度上，并以几种不同的能量进行：质子在类似人体组织的塑料块的不同深度上进行计数。这些质子范围的QA测量需要大量的时间来设置和调整不同的能量：整个过程可能需要一个多小时。目前，伦敦大学学院正在开发一种探测器，以提供更快、更准确的质子范围测量，以加快日常质量保证过程。伦敦大学学院正在与世界质子治疗控制系统的领导者Cosylab合作，为该探测器开发电子设备，以及重建探测器测量的质子范围所必需的软件。此外，通过利用Cosylab在控制现代临床质子治疗中心所需软件方面的专业知识，可以从主治疗控制系统操作和监控探测器，从而更容易进行QA测量。此外，Cosylab在生产商业临床设备方面拥有十多年的经验，将指导完整探测器的开发，以确保其获得必要的医疗和监管批准。

Modern cancer treatment is largely a combination of 3 techniques: surgery, chemotherapy and radiotherapy. Radiotherapy uses beams of X-rays to irradiate the tumour from many different directions. The effect is to kill the cancer by depositing as much radiation dose in the tumour as possible, whilst minimising the dose to the surrounding area to spare healthy tissue.Proton therapy is a more precise form of radiotherapy that provides significant benefits over conventional X-ray radiotherapy. Protons lose energy - and therefore deposit their dose - in a much smaller region within the body, making the treatment much more precise: this leads to a more effective cancer treatment with a smaller chance of the cancer recurring. This is particularly important in the treatment of deep-lying tumours in the head, neck and central nervous system, particularly for children whose bodies are still developing and are particularly vulnerable to long-term radiation damage. The advantages of proton therapy, coupled to the reduced cost of the equipment, has led to a surge in interest in proton therapy treatment worldwide: there are now over 20 centres, with this number set to double every 3 years over the next decade. The UK is currently constructing 2 full-sized proton therapy centres, to be based at University College Hospital in London and The Christie in Manchester and funded by the NHS. These will provide treatment for a much wider range of cancers, allowing more patients to be treated closer to home.Treating these cancers requires machinery that is significantly more complex than a conventional radiotherapy system. Protons are accelerated to the right energy for treatment by a particle accelerator: once the beam leaves the accelerator, it then has to be transported to the treatment rooms many metres away by a series of steering and focussing magnets. When the proton beam reaches the treatment room, it has to be delivered through a gantry to the correct place. Proton therapy gantries are enormous - more than 3 storeys tall and weighing more than a hundred tonnes - and have to rotate around the patient to deliver the beam from any angle with millimetre precision. In order to ensure that treatment with such complex machinery is carried out safely, a range of quality assurance (QA) procedures are carried out each day before treatment starts. The majority of this time is spent verifying that the proton beam travels the correct depth and is carried out for several different energies: protons are counted at different depths in a plastic block that resembles human tissue. These QA measurements of the proton range take significant time to set up and adjust for different energies: the full procedure can take over an hour.A detector is currently under development at UCL to provide faster and more accurate proton range measurements to speed up the daily QA process. UCL is working with Cosylab, the world's leader in control systems for proton therapy, to develop the electronics for this detector, as well as the software that is necessary to reconstruct the proton range measured by the detector. In addition, by taking advantage of Cosylab's expertise in the software needed to control modern clinical proton therapy centres, it will be possible to operate and monitor the detector from the main treatment control system, making it easier to make the QA measurements. Also, with over a decade of experience in producing commercial clinical devices, Cosylab will guide the development of the complete detector in order to make sure that it achieves the necessary medical and regulatory approval.