QuADProBe: Quality Assurance Detector for Proton Beam Therapy

现代癌症治疗在很大程度上是三种技术的结合：手术、化疗和放射治疗。放射治疗使用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症，同时将对周围区域的辐射剂量降至最低，以节省健康组织。质子疗法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--因此将其剂量储存在体内一个小得多的区域--使治疗变得更加精确：这导致了更有效的癌症治疗，癌症复发的可能性更小。这在治疗头部、颈部和中枢神经系统的深层肿瘤方面尤其重要，特别是对身体仍在发育中、特别容易受到长期辐射损害的儿童。质子治疗的优势，加上设备成本的下降，导致世界各地对质子治疗的兴趣激增：现在有100多个中心，这个数字目前每3年翻一番。在英国，NHS资助了两个全尺寸的质子治疗中心-伦敦的大学学院医院和曼彻斯特的克里斯蒂-与克莱特布里奇癌症中心的眼科治疗设施一起运作。这些治疗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械设备。质子被粒子加速器加速到合适的能量以进行处理：一旦束流离开加速器，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，它必须通过龙门送到正确的位置。质子治疗机架非常巨大--超过3层楼高，重量超过100吨--必须绕着患者旋转，才能从任何角度以毫米级的精度发射光束。为了确保使用这种复杂机械的治疗是安全进行的，每天在治疗开始之前都会进行一系列的质量保证(QA)程序。这意味着检查质子束是否处于正确的位置、形状和大小是否正确、传播深度是否正确：必须检查一系列不同的束流位置和能量，以确保治疗是安全的。这些QA测量需要相当长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。我们正在开发一种探测器，它可以比现有系统更快、更准确地测量质子束的大小、位置和射程。探测器由两部分组成。第一种是由两组相互垂直安装的闪烁光纤组成的轮廓监测器，当质子束通过时，它们会发光。这种光可以用光电二极管测量，以确定光束的大小和位置。在它的后面是一个探测器，它是由一层层塑料闪烁体建造的，看起来像一条切成薄片的面包。通过闪烁体堆叠的质子在每一层中储存能量，这些能量被转化为光：通过记录来自每一层的光，可以测量质子沿其路径储存的能量的量。这样的系统提供了对组织中质子范围的直接测量，因为塑料的吸收几乎与人体组织相同。因此，整个上午光束质量保证程序可以在几分钟内完成，在大小、位置和范围上的精度远远低于一毫米。在两个新的NHS中心，这将转化为每天能够额外治疗12-18名患者。

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 falling cost of the equipment, has led to a surge in interest in proton therapy treatment worldwide: there are now over 100 centres, with this number currently doubling every 3 years. In the UK, the NHS has funded 2 full-sized proton therapy centres - at University College Hospital in London and The Christie in Manchester - to operate alongside the eye treatment facility at the Clatterbridge Cancer Centre. 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. This means checking that the proton beam is in the correct position, is the right shape and size, and travels the correct depth: this must be checked for a range of different beam positions and energies to ensure treatment is safe. These QA measurements take significant time to set up and adjust for different energies: the full procedure can take over an hour.We are developing a detector that can make faster and more accurate measurements of the proton beam size, position and range than existing systems. The detector is made of two parts. The first is a profile monitor made of two arrays of scintillating optical fibres, mounted at right angles to each other, that emit light when the proton beam passes through. This light can be measured with photodiodes to determine the beam size and position. Behind this is a detector built from layers of plastic scintillator that resembles a sliced loaf of broad. Protons passing through this scintillator stack deposit energy in each layer which is converted into light: by recording the light from each layer, the amount of energy the protons deposit along their path can be measured. Such a system provides a direct measurement of the range of protons in tissue, since the absorption of the plastic is virtually identical to human tissue. As such, the full morning beam QA procedure could be carried out in a few minutes, with an accuracy well below a millimetre in size, position and range. At the two new NHS centres, this would translate into being able to treat an extra 12-18 patients every single day.