Quality Assurance Range Calorimeter 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，导致全世界对质子治疗的兴趣激增：现在有70多个中心，这一数字目前每3年翻一番。在英国，NHS资助了两个全尺寸质子治疗中心，分别位于伦敦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。其中相当一部分时间用于验证质子束是否能到达正确的深度，并以几种不同的能量进行：质子在模拟人体组织的材料（如ware）中的不同深度进行计数。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。这个项目的重点是开发一种探测器，它可以比现有的系统更快、更准确地测量质子范围。该探测器由多层塑料闪烁体构成，其密度与水相同，类似于切片的宽面包。通过这个闪烁体堆栈的质子在每一层沉积能量，这些能量转化为光：通过记录每一层的光，质子在其路径上沉积的能量就可以被测量出来。这种系统提供了对组织中质子范围的直接测量，因为塑料的吸收几乎与人体组织相同。因此，对多个能量的质子范围的测量将允许在几分钟内完成早晨能量QA程序，精度小于一毫米。在两个新的NHS中心，这将转化为每天能够治疗额外的12-18名患者。一个原型探测器正在伦敦大学学院组装和测试，目的是开发一个完整的商业系统，可以以必要的速度和精度进行范围QA测量。

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 70 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. A significant fraction 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 material, like ware, that mimics 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.The focus of this project is to develop a detector that can make faster and more accurate measurements of the proton range than existing systems. The detector is built from layers of plastic scintillator that has the same density as water and 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, a measurement of the proton range for multiple energies would allow the complete morning energy QA procedure to be carried out in a few minutes, with an accuracy of less than a millimetre. At the two new NHS centres, this would translate into being able to treat an extra 12-18 patients every single day. A prototype detector is being assembled and tested at UCL with the intention to develop a full commercial system that can make range QA measurements with the necessary speed and accuracy.