Probe: Proton beam Extension for Imaging and Therapy

英国目前正在签订合同，提供两个中心，NHS将在那里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称为强度调制放射疗法（IMRT）的技术提供出色的治疗，但是仍然存在小剂量固有地沉积在预期肿瘤治疗部位之外的组织中。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。质子治疗可以做到这一点，因为质子在组织中的相互作用与X射线完全不同;在输送的剂量中有一个更明显的峰值，可以在深度上变化以准确地靶向肿瘤。位于伦敦的克里斯蒂医院和UCLH的两个新中心可以在任何深度进行治疗，因为它们将使用高能加速器，增强目前位于克拉特布里奇的低能质子中心，该中心仅限于浅层眼睛治疗。虽然质子剂量沉积在特定深度，但很难设置适当的能量以达到该深度。这是因为目前的成像技术，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慢的数量方面做得不够好。一种有希望的方法是用质子成像：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，在那里测量它们的剩余能量，以计算出在途中损失了多少。英国正在研制适合的高分辨率探测器，但目前还没有合适的质子源，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，我们认为我们可以建立一个线性加速器（linac），可以将质子从目前成人治疗中心（如克里斯蒂）可用的能量提高到成像所需的能量。为了改造现有的治疗中心，需要这样的直线加速器是小的，因此，能量增益必须发生在一个非常短的距离;这是困难的部分，并需要使用高频（“X波段”）加速腔先前开发用于粒子物理实验。我们希望在这个项目中展示第一个真正的高梯度质子直线加速器的成像，采取以前开发的物理研究的知识。我们的目标是在开发一个高梯度直线加速器是，它可以用来提供改善成像的病人在英国和国外。据认为，使用质子改进成像可以将肿瘤治疗期间所需的边缘减少多达5 mm，从而保护周围的敏感组织，从而减少副作用并改善患者的长期结局。后来，我们认为同样的直线加速器技术也可以用于直接提供质子进行治疗，其中使用直线加速器可以更好地控制治疗深度。此外，如果加速结构可以做得足够小，它们甚至可以安装在围绕患者旋转质子束的机架上，这意味着更小，更便宜的治疗设施成为可能。这些单间中心被视为增加患者获得质子治疗的一种方式。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的癌症范围。

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.