Calorimetry for Proton 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。质子治疗的效果是通过在肿瘤中储存尽可能多的辐射剂量来杀死癌症。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，尤其是对身体仍在发育中、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的质子治疗中心，分别设在伦敦的大学学院医院和曼彻斯特的克里斯蒂。这些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。这些中心的采购工作于2013年开始，预计将在2018年后的某个时候开启。与世界各地的大多数质子治疗中心不同，特别是在美国，这两个英国中心是由公共资金资助的，将治疗一些最具挑战性的癌症。为了治疗这些困难的癌症，需要极其复杂的成像来识别癌症并保留周围组织。传统的X光治疗计划需要多次CT扫描来创建患者治疗计划，并在治疗过程中监测癌症的大小和位置。然而，由于质子比X射线精确得多，成像质量也必须好得多。此外，X射线CT图像不提供质子如何损失能量的信息，因此必须使用换算系数来估计剂量将如何通过质子而不是X射线传递。此外，在现有的质子治疗中心，CT扫描不是在患者就位并准备接受治疗时进行的，因为很难将成像设备挤在质子输送喷嘴周围。当患者移动时，他们的身体形状会发生变化，使得治疗计划不那么准确。另一种选择是在患者坐在准备治疗的位置时，使用更高能量的质子来为患者成像。质子的能量会增加，这样它们就会穿透身体：通过跟踪患者前后的质子并测量它们的能量，可以重建患者处于正确位置的肿瘤和周围组织的图像，这也可以告诉你在治疗期间质子将沉积多少剂量。这个系统被称为质子CT。为了创建质子CT图像，当质子离开人体时，你需要非常准确地测量质子能量。这个项目正在考虑修改一种特殊类型的能量探测器，称为热量计，以测量质子CT系统中的质子能量。量热计是为超NEMO实验开发的，用于测量高能电子，但它也可以非常精确地测量质子能量。此外，它还可以测量用于治疗的质子束的能量。该探测器还将用于检查克莱特布里奇癌症中心使用较低能量质子治疗眼部肿瘤的质子束的能量。克莱特布里奇是英国唯一一家这样的医院。

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.In order to treat such difficult cancers, extremely sophisticated imaging is needed to identify the cancer and spare the surrounding tissue. Traditional treatment planning with X-rays requires multiple CT scans to create a patient treatment plan and to monitor the size and position of the cancer during treatment. However, since protons are much more precise than X-rays, the quality of the imaging must also be that much better. In addition, X-ray CT images don't provide information on how protons lose energy, so a conversion factor has to be used to estimate how the dose will be delivered with protons rather than X-rays. Also, in existing proton therapy centres CT scans are not taken with the patient in position and ready for treatment, since it's very difficult to squeeze the imaging equipment around the proton delivery nozzle. When the patient moves the shape of their body changes, making the treatment plan less accurate.An alternative is to use higher energy protons to image the patient while the patient is sitting in position ready for treatment. The energy of the protons is increased so that they penetrate right through the body: by tracking the protons before and after the patient and measuring their energy, it's possible to reconstruct an image of the tumour and the surrounding tissue with the patient in the right position, that also tells you how much dose the protons will deposit during treatment. This system is called proton CT.In order to create a proton CT image, you need a very accurate measurement of the proton energy when it leaves the body. This project is looking at modifying a particular type of energy detector, called a calorimeter, to measure the energy of protons in a proton CT system. The calorimeter was developed for the SuperNEMO experiment to measure high energy electrons but it can also measure proton energies very accurately. In addition, it can also measure the energy of the proton beam that is used for treatment. This detector will also be used to check the energy of the proton beam at the Clatterbridge Cancer Centre that uses lower energy protons to treat eye tumours. Clatterbridge is the only hospital of its kind in the UK.