新加坡国立大学牵头的一项国际研究合作开发了一种新技术，通过加速H₂⁺离子并使用新型二维碳膜将其分裂成质子束，有望提升癌症质子治疗的精度。该技术利用了特殊的非晶碳膜（UC-MAC），其独特的无序结构能有效减少质子散射，实现高空间精度。通过一种名为“无序到无序”（DTD）的创新制造方法，研究人员实现了8英寸晶圆级别的UC-MAC薄膜生产，速度比传统方法快十倍。这种高品质的质子束能够更精确地靶向肿瘤，减少对周围健康组织的损伤，并为FLASH疗法等前沿治疗手段提供了可能。该研究成果标志着质子治疗领域的一项重要进展，为更精准、更经济的癌症治疗带来了新希望。

🔬 **新型质子束生成技术提升癌症治疗精度**：研究团队开发了一种通过加速H₂⁺离子并使用二维碳膜将其分裂为质子束的新方法。与直接加速质子相比，加速H₂⁺离子可以显著减弱粒子间的相互排斥效应，从而实现比现有回旋加速器高一个数量级的质子束流，使质子治疗更快、更精确，并能更有效地瞄准肿瘤。这对于治疗位于精密或关键器官内的肿瘤尤为重要。

💎 **非晶碳膜（UC-MAC）的独特性能**：该技术的关键在于使用一种名为“超净单层非晶碳”（UC-MAC）的新型二维碳材料。与石墨烯有序的蜂窝状结构不同，UC-MAC具有由五至八元碳环组成的无序混合结构，这种无序性产生了微小的孔隙，能够在H₂⁺离子通过时将其分裂成质子。实验表明，UC-MAC膜产生的质子散射远少于石墨烯、非超净非晶碳和商业碳薄膜，显著提高了质子束的质量和空间精度。

🚀 **“无序到无序”策略实现工业化生产**：为了克服非晶碳薄膜制造的挑战，研究人员提出了一种创新的“无序到无序”（DTD）制造策略。该方法通过等离子体增强化学气相沉积（CVD）技术，在铜基底上生长MAC薄膜，通过抑制长程有序来获得所需的无序结构。这种方法不仅能够实现8英寸晶圆级别的生产，而且速度比传统CVD方法快十倍，为UC-MAC材料的工业化应用奠定了基础。

🎯 **减少散射，实现高精度靶向**：通过测量H₂⁺离子分裂产生的双质子事件（作为质子散射的指标），研究发现UC-MAC膜的散射事件数量远低于其他材料。UC-MAC产生的质子束具有极高的空间精度和极低的散射，这使得质子治疗能够更精确地对准肿瘤，尤其是在处理精密或关键器官附近的肿瘤时，能够最大程度地减少对健康组织的损害。

💡 **未来展望：更精准、更经济的质子疗法**：研究团队正基于这项成果，开发基于二维非晶材料的单分子离子反应平台，并结合高能离子纳米束系统。他们的目标是进一步提高质子束在癌症治疗中的精度，同时降低成本，并使其在临床应用中更加便捷易用，为癌症患者带来更优的治疗选择。

A new method for generating high-energy proton beams could one day improve the precision of proton therapy for treating cancer. Developed by an international research collaboration headed up at the National University of Singapore, the technique involves accelerating H₂⁺ ions and then using a novel two-dimensional carbon membrane to split the high-energy ion beam into beams of protons.

One obstacle when accelerating large numbers of protons together is that they all carry the same positive charge and thus naturally repel each other. This so-called space–charge effect makes it difficult to keep the beam tight and focused.

“By accelerating H₂⁺ ions instead of single protons, the particles don’t repel each other as strongly,” says project leader Jiong Lu. “This enables delivery of proton beam currents up to an order of magnitude higher than those from existing cyclotrons.”

Lu explains that a high-current proton beam can deliver more protons in a shorter time, making proton treatments quicker, more precise and targeting tumours more effectively. Such a proton beam could also be employed in FLASH therapy, an emerging treatment that delivers therapeutic radiation at ultrahigh dose rates to reduce normal tissue toxicity while preserving anti-tumour activity.

Industry-compatible fabrication

The key to this technique lies in the choice of an optimal membrane with which to split the H₂⁺ ions. For this task, Lu and colleagues developed a new material – ultraclean monolayer amorphous carbon (UC-MAC). MAC is similar in structure to graphene, but instead of an ordered honeycomb structure of hexagonal rings, it contains a disordered mix of five-, six-, seven and eight-membered carbon rings. This disorder creates angstrom-scale pores in the films, which can be used to split the H₂⁺ ions into protons as they pass through.

Scaling the manufacture of ultrathin MAC films, however, has previously proved challenging, with no industrial synthesis method available. To address this problem, the researchers proposed a new fabrication approach in which the emergence of long-range order in the material is suppressed, not by the conventional approach of low-temperature growth, but by a novel disorder-to-disorder (DTD) strategy.

DTD synthesis uses plasma-enhanced chemical vapor deposition (CVD) to create a MAC film on a copper substrate containing numerous nanoscale crystalline grains. This disordered substrate induces high levels of randomized nucleation in the carbon layer and disrupts long-range order. The approach enabled wafer-scale (8-inch) production of UC-MAC films within just 3 s – an order of magnitude faster than conventional CVD methods.

Disorder creates precision

To assess the ability of UC-MAC to split H₂⁺ ions into protons, the researchers generated a high-energy H₂⁺ nanobeam and focused it onto a freestanding two-dimensional UC-MAC crystal. This resulted in the ion beam splitting to create high-precision proton beams. For comparison they repeated the experiment (with beam current stabilities controlled within 10%) using single-crystal graphene, non-clean MAC with metal impurities and commercial carbon thin films (8 nm).

Measuring double-proton events – in which two proton signals are detected from a single H₂⁺ ion splitting – as an indicator for proton scattering revealed that the UC-MAC membrane produced far fewer unwanted scattered protons than the other films. Ion splitting using UC-MAC resulted in about 47 double-proton events over a 20 s collection time, while the graphene film exhibited roughly twice this number and the non-clean MAC slightly more. The carbon thin film generated around 46 times more scattering events.

The researchers point out that the reduced double-proton events in UC-MAC “demonstrate its superior ability to minimize proton scattering compared with commercial materials”. They note that as well as UC-MAC creating a superior quality proton beam, the technique provides control over the splitting rate, with yields ranging from 88.8 to 296.0 proton events per second per detector.

“Using UC-MAC to split H₂⁺ produces a highly sharpened, high-energy proton beam with minimal scattering and high spatial precision,” says Lu. “This allows more precise targeting in proton therapy – particularly for tumours in delicate or critical organs.”

“Building on our achievement of producing proton beams with greatly reduced scattering, our team is now developing single molecule ion reaction platforms based on two-dimensional amorphous materials using high-energy ion nanobeam systems,” he tells Physics World. “Our goal is to make proton beams for cancer therapy even more precise, more affordable and easier to use in clinical settings.”

The study is reported in Nature Nanotechnology.

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