QuADProBe: Quality Assurance Detector for Proton Beam Therapy

现代癌症治疗主要是3种技术的组合：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。质子治疗是一种更精确的放射疗法，与传统的X射线放射疗法相比，质子治疗具有更大的优势。质子治疗是一种更精确的放射疗法，它可以通过在肿瘤中沉积尽可能多的辐射剂量来杀死癌症，同时将周围区域的辐射剂量降至最低，以保护健康组织。质子失去能量--因此存款其剂量--在体内一个小得多的区域，使治疗更加精确：这导致更有效的癌症治疗，癌症复发的机会更小。这对于治疗头部、颈部和中枢神经系统的深部肿瘤特别重要，特别是对于身体仍在发育中、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，导致全世界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--位于伦敦的大学学院医院和曼彻斯特的克里斯蒂医院--与克拉特布里奇癌症中心的眼科治疗设施一起运作。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合适的能量进行治疗：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运送到数米之外的治疗室。当质子束到达治疗室时，它必须通过机架输送到正确的位置。质子治疗台架是巨大的-超过3层楼高，重量超过100吨-并且必须围绕患者旋转，以毫米精度从任何角度提供光束。为了确保使用这种复杂的机械进行安全处理，每天在处理开始前都要执行一系列质量保证（QA）程序。这意味着检查质子束是否处于正确的位置，是否具有正确的形状和大小，以及是否经过正确的深度：必须检查一系列不同的射束位置和能量，以确保治疗安全。这些QA测量需要大量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，可以比现有系统更快，更准确地测量质子束的大小，位置和范围。探测器由两部分组成。第一种是由两组平行排列的光纤组成的轮廓监测器，它们相互垂直安装，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。在这后面是一个由塑料闪烁体层制成的探测器，类似于一个切片的面包。穿过该闪烁体堆叠的质子在每层中存款能量，该能量被转换成光：通过记录来自每层的光，可以测量质子存款沿着它们的路径的能量的量。这种系统提供了对组织中质子范围的直接测量，因为塑料的吸收实际上与人体组织相同。因此，整个上午波束质量保证程序可以在几分钟内进行，其尺寸、位置和范围的精度远低于一毫米。在两个新的NHS中心，这将意味着每天能够治疗额外的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.