Antiprotons: effects on biological matter and evaluation as a novel radiotherapy

手术后，放射治疗是最广泛使用和最成功的治疗癌症的方法。然而，现代放射治疗计划往往会对患者造成严重的副作用，总体成功率仍然只有中等。因此，有必要研究新的放射治疗方法，以便为未来的新治疗方法提供信息和改进。放射治疗的工作原理是杀死癌细胞-通常是通过破坏这些细胞中的DNA。如果损伤严重到细胞无法修复，细胞就会死亡。许多关于放射治疗的研究都是为了了解细胞对不同类型和剂量的辐射的反应。放射治疗产生副作用的原因之一是因为健康细胞和癌细胞都被破坏或杀死。因此，人们已经做出了相当大的努力，以尽量减少这些影响，并集中对肿瘤细胞的辐射破坏力。在某种程度上，这已经通过X射线从多个外部部位照射患者来实现。另一种非常有前途的方法是使用离子束代替X射线。全世界已经有许多质子治疗设施（包括英国的一个），使用较重离子（如碳）的中心现在正在投入使用。离子束的巨大优势是由于它们在组织中存款能量的方式。当X射线束进入人体时，能量在进入人体后立即沉积，从而造成伤害。相比之下，离子束在沉积大部分能量之前可以穿过组织几厘米。通过操纵离子束的物理性质，可以控制离子束存款其能量的深度，并使其对应于肿瘤的位置。因此，这种类型的辐射的破坏力的大部分集中在我们想要摧毁的细胞中。离子束辐照的结果令人印象深刻，提高了清除率，减少了副作用。离子束的进一步改进可能是使用反质子。反质子对任何科幻小说的读者来说都很熟悉-通常是星际飞船的推进手段或可怕的破坏性武器系统。然而，反质子可以在地球上产生，包含，控制和用于实验。像它们的常规物质对应物质子一样，它们可以在沉积能量之前穿过材料几厘米。反质子的潜在优势在于，当反质子与质子相遇时，两个粒子会相互湮灭（根据爱因斯坦著名的方程式E= mc 2），释放出大量的能量。位于瑞士的欧洲核子研究中心（CERN）的一组科学家已经开始实验，看看反质子是否可以用于癌症治疗。这个研究小组（ACE合作）已经证明，反质子杀死细胞的能力大约是质子的四倍。然而，在将反质子应用于癌症放射治疗之前，还需要进行大量的额外科学工作。2008年，申请人加入了ACE合作组织，并在CERN进行了一项实验，研究反质子对培养的人类细胞的影响。他们发现，反质子会对这些细胞中的DNA造成损伤，细胞接触的反质子越多，造成的DNA损伤就越多。此外，他们还证明，来自辐照细胞的培养基可在未辐照细胞中引起DNA损伤反应。这种现象，即所谓的旁观者效应，在其他类型的辐射中得到了很好的证明，但以前没有在反质子辐射中得到证明。申请人现在寻求资金，以便在2009年秋季返回欧洲核子研究中心，继续这些实验。今年，他们希望更多地了解反质子辐射引起的旁观者效应，包括量化这些效应的大小。

After surgery, radiation treatments are the most widely used and successful way to cure cancers. However, modern radiotherapy plans often cause severe side-effects to the patient and the overall success rate is still only moderate. Therefore there is a need to research new ways of delivering radiotherapies in order to inform and improve new treatments in the future.Radiotherapy works by killing cancer cells - usually by breaking the DNA in those cells. If the damage is so severe that the cells cannot repair it, the cells die. A lot of the research into radiotherapy is aimed at understanding how cells respond to radiations of different types and doses.One reason why radiotherapy results in side-effects is because healthy cells are damaged, or killed, as well as cancerous ones. Therefore considerable efforts have been made to minimize these effects and to focus the destructive power of radiation on tumour cells. This has been achieved, to some extent, with X-rays by irradiating the patient from multiple external sites. An alternative, and very promising, approach is the use of ion beams in place of x-rays. There are already numerous proton treatment facilities worldwide (including one in the UK) and centres using heavier ions (eg carbon) are now being brought into operation.The big advantage of ion beams is due to the way they deposit their energy in tissue. When an X-ray beam enters a person, energy is deposited immediately upon entry, thus causing damage. In contrast, ion beams can pass several centimeters through tissue before depositing the bulk of their energy. By manipulation of the physical properties of the ion beam, the depth at which ion beams deposit their energy can be controlled and made to correspond to the site of the tumour. Thus the bulk of this type of radiation's destructive power is concentrated in the cells which we wish to destroy. The results from ion beam irradiation are impressive, with improved clear-up rates and decreased side-effects.A further improvement on ion beams, may be to use antiprotons. Antiprotons will be familiar to any reader of science fiction - usually as the means of propulsion of interstellar starships or in a fearsome and destructive weapons systems. However, antiprotons can be produced here on earth, contained, controlled and used in experiments. Like their regular matter counterparts, protons, they can pass through material for several centimeters before depositing their energy. Their potential advantage arises from the fact that when an antiproton meets a proton, the two particles annihilate each other (according to Einstein's famous equation E=mc2) releasing lots of energy.A group of scientists at the European Centre for Nuclear Research (CERN) in Switzerland have begun experiments to see if antiprotons can be used in cancer therapies. This group (the ACE collaboration) have shown that antiprotons kill cells approximately four time better than protons. However, before antiprotons can be considered a viable possibility in cancer radiotherapy, considerable extra scientific work is required.In 2008, the applicants joined the ACE collaboration and carried out an experiment at CERN to investigate the effects of antiprotons on cultured human cells. They showed that antiprotons cause damage to the DNA in these cells and that the more antiprotons the cells are exposed to, the more DNA damage is caused. In addition, they demonstrated that media from irradiated cells can cause DNA damage responses in non-irradiated cells. This phenomenon, the so-called bystander effect, is well documented with other types of radiation, but has not previously been shown with antiproton irradiation.The applicants now seek funding to return to CERN in autumn 2009, in order to continue these experiments. This year they hope to learn more about the bystander effect resulting from antiproton irradiation, including quantifying the magnitude of these effects.