High Resolution Fast Detector for Quality Assurance in 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沉积尽可能多的辐射剂量来杀死癌细胞。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。2011年，英国政府宣布资助两个全尺寸质子治疗中心，分别设在伦敦大学学院医院和曼彻斯特的克里斯蒂医院。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。这些中心的采购始于2013年，预计将在2018年之后的某个时间开放。与世界上大多数质子治疗中心（尤其是美国的质子治疗中心）不同，英国的两家质子治疗中心是由政府资助的，将治疗一些最具挑战性的癌症。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。这些能量QA测量需要花费大量时间来设置和调整不同的能量：整个过程通常需要一个小时。该项目旨在开发一种探测器，它将比现有系统更准确、更快速地测量质子能量。为SuperNEMO高能物理实验开发的用于测量粒子能量的量热计已经被修改，可以记录质子治疗束的能量。该系统可以比现有的能量QA技术更快地测量质子束能量，主要是因为它简单得多。质子被塑料闪烁体吸收，将粒子能量转化为光，然后可以检测到这种光来测量粒子能量。通过使闪烁体的大小和形状合适，可以在不改变探测器系统任何东西的情况下测量整个处理能量范围内的质子束。这将允许在几分钟内完成整个上午的能量质量保证程序。在英国的两家中心，这将意味着每天能够治疗额外的12名患者。此外，由于如此多的光是由停在闪烁体中的质子产生的，质子能量可以测量到超过1%。这意味着能量测量的准确性也将优于现有技术。

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.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.In 2011 the UK government announced funding for 2 full-sized proton therapy centres, to be based at University College Hospital in London and The Christie in Manchester. These will provide treatment for a much wider range of cancers, allowing more patients to be treated closer to home. Procurement for these centres began in 2013, with doors expected to open some time after 2018. Unlike the majority of proton therapy centres worldwide - particularly in the US - the 2 UK centres are publicly funded and will treat some of the most challenging cancers.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 energy QA measurements take significant time to set up and adjust for different energies: the full procedure normally takes an hour.This project is looking to develop a detector that will make more accurate and more rapid measurements of the proton energy than existing systems. A calorimeter - used to measure a particle's energy - that was developed for the SuperNEMO high energy physics experiment has been modified to record the energy of a proton therapy treatment beam. This system can measure proton beam energies much more quickly than the existing energy QA technology primarily because it is much simpler. Protons are absorbed by a plastic scintillator that converts the particle energy into light: this light can then be detected to measure the particle energy. By making the scintillator the right size and shape, proton beams over the full range of treatment energies can be measured without having to change anything about the detector system. This would allow the complete morning energy QA procedure to be carried out in a few minutes. At the two UK centres, this would translate into being able to treat an extra 12 patients every single day.In addition, because so much light is produced by protons stopping in the scintillator, the proton energy can be measured to better than 1%. This means that the accuracy of the energy measurement will also be better than the existing technology.