Probe: Proton beam Extension for Imaging and Therapy

英国目前正在签约提供两个中心，NHS将在那里使用质子治疗许多癌症。虽然当前一代的X射线直线加速器可以使用被称为调强放射治疗(IMRT)的技术提供出色的治疗，但仍有少量的固有剂量沉积在预期的肿瘤治疗部位以外的组织中。对于某些靠近关键器官的难以治疗的肿瘤，特别是在治疗一些儿童癌症时，避免这种所谓的场外剂量将是有益的。质子疗法之所以能做到这一点，是因为质子在组织中的相互作用与X射线截然不同；在提供的剂量中有一个更明显的峰值，该峰值可以在深度上变化，以准确地靶向肿瘤。位于伦敦克里斯蒂医院和伦敦城市大学附属医院的两个新中心可以进行任何深度的治疗，因为他们将使用高能加速器，扩大目前克莱特布里奇的低能质子中心，该中心仅限于浅眼治疗。但这存在一个问题。虽然质子剂量是在特定深度沉积的，但很难设置合适的能量来达到该深度。这是因为当前一代的成像技术，如X射线计算机断层扫描，在让临床医生估计质子在到达肿瘤的过程中会减速的数量方面做得不够好。解决这一问题的一个有希望的方法是对质子也进行成像：不需要从X射线测量中进行转换，但质子成像需要更高能量的质子，这些质子可以直接穿过患者，在那里测量其剩余能量，以计算出在此过程中损失了多少。英国正在开发合适的高分辨率探测器，但到目前为止还没有合适的质子来源。这就是我们的直线加速器的用武之地。我们研究所和其他地方最近的研究表明，我们认为可以建造一种直线加速器(直线加速器)，可以将目前克里斯蒂等成人治疗中心可用能量中的质子提高到成像所需的能量。要改装到现有的治疗中心，需要这样的直线加速器很小，因此必须在很短的距离内获得能量；这是困难的部分，需要使用以前为粒子物理实验开发的高频(X波段)加速腔。我们希望在这个项目中展示第一个真正用于成像的高梯度质子直线加速器，利用之前为物理研究开发的知识。我们开发高梯度直线加速器的目标是它可以用于为英国和国外的患者提供更好的成像。人们认为，使用质子的改进成像可以将肿瘤治疗过程中所需的边际减少多达5毫米，节省周围敏感组织，从而减少副作用，改善患者的长期结果。后来，我们认为同样的直线加速器技术也可以用于直接为治疗提供质子，其中使用加速器可以更精细地控制治疗深度。此外，如果加速结构可以制造得足够小，它们甚至可以安装在围绕患者旋转质子束的门架上，这意味着更小、更便宜的治疗设施成为可能。这些单室中心被视为增加患者获得质子治疗的途径之一。我们希望我们的项目及其带来的优势将在未来扩大质子治疗有益于癌症的范围。

The UK is presently contracting to supply two centres where the NHS will carry out treatment of many cancers with protons. Whilst the current generation of X-ray linacs can deliver excellent treatment using the technique known as intensity-modulated radiotherapy (IMRT), there is nevertheless a small dose inherently deposited in tissues outside of the intended tumour treatment site. For certain hard-to-treat tumours near to critical organs, and in particular when treating some childhood cancers, it would be beneficial to avoid this so-called out-of-field dose. Proton therapy can do this because protons interact in tissue quite differently to X-rays; there is a much more pronounced peak in the delivered dose which can be varied in depth to target the tumour accurately. The two new centres at Christie Hospital and UCLH in London can treat at any depth as they will use high-energy accelerators, augmenting the present low-energy proton centre at Clatterbridge which is restricted to shallow eye treatments.But there's a problem. Whilst the proton dose is deposited at a specific depth, it can be hard to set the proper energy to reach that depth. This is because current-generation imaging such as X-ray computed tomography doesn't do a good enough job at allowing clinicians to estimate the amount the protons will slow down on their way to the tumour. One promising way around this is to do imaging with protons as well: no conversion from X-ray measurements is needed, but proton imaging needs more energetic protons that can pass right through the patient where their residual energy is measured to work out how much was lost on the way. Suitable high-resolution detectors for this are under development in the UK, but as yet there is no suitable source of the protons themselves.This is where our linac comes into the story. Recent research at our institute and elsewhere means that we think we can build a linear accelerator (linac) that can boost the protons from the energy available at present adult treatment centres such as Christie up to the energies required for imaging. To retrofit to existing treatment centres requires such a linac to be small, and hence that energy gain must occur in a very short distance; this is the hard part, and requires the use of high-frequency ('X band') accelerating cavities previously developed for use in particle physics experiments. We hope in this project to demonstrate the first truly high-gradient proton linac for imaging, taking the knowledge previously developed for physics research.Our aim in developing a high-gradient linac is that it can be used to provide improved imaging for patients in the UK and abroad. It is thought that improved imaging using protons could reduce the required margins during tumour treatment by as much as 5mm, sparing surrounding sensitive tissues and thereby reducing side-effects and improving long-term outcomes for patients. Later on, we think the same linac technology could also be used to provide protons directly for treatment, where the use of a linac can allow finer control of the treatment depth. Also, if the accelerating structures can be made small enough, they could even themselves be fitted onto the gantry that rotates the proton beam around the patient, meaning that smaller, cheaper treatment facilities become possible. These single-room centres are seen as one way to increase the access to proton therapy for patients.We hope our project and the advantages it brings will in the future widen the range of cancers for which proton therapy is beneficial.