Ion Beam Radiotherapies: Comparison of Protons, Antiprotons and Heavier Ions

辐射可以致癌，但也可以用来治疗癌症。放疗的确比化疗应用更广泛。它的工作原理是破坏细胞中的DNA分子，导致细胞死亡。然而，放射治疗有一个主要问题：它不是一个非常有选择性的方法，经常损害健康组织，同时杀死肿瘤。因此，在确保治疗仍能摧毁肿瘤的同时，寻找最小化这种损害的方法已经做了大量的工作。提高辐射目标的一种方法是使用离子束（而不是通常使用的x射线）。这是有效的，因为离子在第一次进入人体时不会损失太多能量（不像x射线，它在进入人体的那一刻就开始积蓄能量，从而造成伤害）。相反，它们在进入人体的精确距离处，即所谓的布拉格峰处，损失了大部分能量。布拉格峰的位置取决于离子运动的速度和它们的类型。所以这个位置可以被控制，使它与肿瘤相对应。这使得辐射的破坏力集中在肿瘤上，很大程度上不影响周围的健康组织。利用氢离子（质子）治疗癌症的设施在世界上许多国家都在使用。结果令人印象深刻，治疗成功率提高，副作用减少。NHS已经认识到这一潜力，并计划建立一个新的质子设施。然而，最现代的设施使用来自碳等较重元素的离子。甚至有人建议可以使用反物质离子。虽然这听起来像是科幻小说里的情节，但反质子是可以在地球上制造出来的。它们的行为很像普通的质子，穿过物质并将大部分能量沉积在布拉格峰上。然而，当反质子和质子相遇时，它们会相互湮灭，释放出更多的能量。所以它们有可能比质子更有效，因为有额外的能量释放。我们已经启动了一项实验计划，比较质子、碳离子和反质子如何与生物物质相互作用。我们想要比较和对比这些不同形式的辐射。特别是，我们想了解它们是如何破坏细胞中的DNA的。关于反质子如何破坏细胞DNA，我们已经了解了很多。所以我们想完成这些实验，并把它们扩展到质子和碳离子。我们将观察这些类型的辐射是否会导致染色体（细胞中包含DNA的结构）发生根本性的改变。我们将观察辐照细胞是否能修复受损的DNA，以及修复的速度。这很重要，因为在放射治疗中我们想要造成不可修复的损伤。当不可修复的损伤发生时，细胞通常会以一种叫做凋亡的特殊细胞死亡方式自杀。我们还将观察细胞的染色体，看看是否发生了结构上的重大变化。虽然我们可以从完整的细胞中了解到很多，但它们有时太复杂了。所以我们计划使用一种叫做质粒的特殊类型的DNA分子，因为有一种直接的方法来观察它们是在一条链上断裂，还是在两条链上断裂，或者在很多地方断裂。我们也可以用这种方法来量化伤害，并找出特定程度的伤害需要多少辐射。所以我们应该可以比较辐射。然而，我们不能在英国做这些实验。世界上只有一个能量充足的反质子源——日内瓦的欧洲核子研究中心。也没有临床相关能量的碳离子来源。因此，我们计划前往卡塔尼亚（意大利）做这些实验。研究结果不仅会引起寻找潜在的新型癌症治疗方法的肿瘤学家的兴趣，也会引起许多想要了解辐射如何与生物物质相互作用的科学家的兴趣。

Radiation can cause cancer, but it can also be used to cure the disease. Indeed radiotherapy is more widely used than chemotherapy. It works by breaking DNA molecules in cells, which causes these cells to die. However, radiotherapy has a major problem: it isn't a very selective method and often damages healthy tissue, as well as killing the tumour. So a lot of work has gone into finding ways to minimise this damage, while making sure that the treatment still destroys the tumour.One way to improve the targeting of radiation is to use beams of ions (instead of x-rays, which are normally used). This works because ions do not lose much energy when they first enter the body (unlike x-rays which start depositing energy, and therefore causing damage, the moment they enter you). Instead they lose most of their energy at a precise distance into the body, at the so-called Bragg peak. The position of this Bragg peak depends on how fast the ions are travelling and what type of ions they are. So the position can be controlled such that it corresponds to the tumour. This enables the destructive power of the radiation to be focussed into the tumour, largely sparing surrounding, healthy tissues.Facilities which use hydrogen ions (protons) to treat cancer patients are in use in many countries worldwide. The results are impressive with improved treatment success and reduced side-effects. The NHS has recognised this potential and plans to build a new proton facility.However, the most modern facilities use ions from heavier elements such as carbon. It has even been suggested that ions of antimatter could be used. Although this sounds like something from a science fiction story, anti-protons can be made here on earth. They behave a lot like regular protons, passing through matter and depositing most of their energy at a Bragg peak. However, when an antiproton and a proton meet, they annihilate each other releasing even more energy. So they have the potential to be more effective than protons, because of this additional energy release.We have initiated a programme of experiments to compare how protons, carbon ions and antiprotons interact with living matter. We want to compare and contrast these different forms of radiation. In particular, we want to learn how they damage DNA in the cell. We have already learned quite a bit about how antiprotons damage cellular DNA. So we want to complete these experiments and extend them to protons and carbon ions. We will see if these types of radiation cause radical alterations to the chromosomes (the structures in cells which contain the DNA). We will see if the irradiated cells can repair their damaged DNA, and how fast they can do it. This is important because in radiotherapy we want to cause non-repairable damage. When irreparable damage occurs, cells often commit suicide in a special type of cell death called apoptosis. We will also look at the cells' chromosomes to see if any gross changes in structure have occurred.Although we can learn a lot from intact cells, they are sometimes just too complex. So we plan to use a special type of DNA molecule called plasmids because there is a straightforward method to see if these have been broken on one strand, both strands or in lots of places. We can also use this method to quantify the damage and find out how much radiation is required for a particular level of damage. So we should be able to compare the radiations.However, we can't do these experiments in the UK. There is only one source of antiprotons at sufficient energy in the world - at CERN in Geneva. Nor is there a source of carbon ions at clinically relevant energies. So for this we plan to travel to Catania (Italy) to do these experiments.The results will be of interest to oncologists looking at potential, novel cancer treatments, but also to a wide range of scientists who want to understand how radiation interacts with living matter.