Since the development of one‐ and two‐million volt x‐ray machines in the 1930s, which led to the reduction of both skin erythema and bone necrosis as well as an increase in depth dose, medical physicists have worked steadily to develop radiation sources and techniques for increasing the therapeutic ratios for most solid tumors. One of the major results of this research was the linear electron accelerator (Linac) operating in the range 4–10 MeV. Starting in the mid‐century, these machines became and remain the work‐horses of radiation therapy; they perform their tasks reliably, at acceptable cost, and with cleverly designed supplemental devices, can treat a wide range of anatomical sites.

Now, after a century of research and development, and the introduction of ever more complex and expensive radiation sources it appears that the efficacy of radiation therapy as a cancer treatment has reached a plateau. For example, proton‐beam therapy (PBT) provides treatment plans with higher therapeutic ratios, which may result in reduced radiation toxicities, but evidence that PBT offers patients longer survival times is in short supply. The following paragraph from the Mayo Clinic's website briefly summarizes the current status of PBT:

“Proton therapy has shown promise in treating several kinds of cancer. Studies have suggested that proton therapy may cause fewer side effects than traditional radiation since doctors can better control where the proton beams deposit their energy. But few studies have directly compared proton therapy radiation and X‐ray radiation, so it's not clear whether proton therapy is more effective in prolonging lives.”

Clearly, differences in survival times and levels of toxicity for PBT as compared with those for x rays are likely to be small. Therefore, to obtain statistically valid comparisons would require that relatively large numbers of patients be studied over long periods of time, and that the methodology of the randomized prospective clinical trial (RPCT) be employed. Given the logistics of running such a trial, it should come as no surprise that such trials in radiation therapy are few and far between. (Perhaps an National Cancer Institute‐sponsored, multi‐institutional RPCT of protons versus x rays for a specific cancer would help to settle this issue.) In the meantime, human nature being what it is, an oncologist who uses PBT may sincerely believe that his patients are doing better than those he used to treat with x rays, but could this not be personal bias in favor of the new machine whose acquisition he may have promoted for several years?

So here we are, up against what has been referred to as “The Emperor of All Maladies”¹, a disease whose ultimate cure will likely come from biological research carried out at university and big‐pharma laboratories. While we wait, albeit impatiently, surgeons, medical oncologists, and radiation oncologists hold the fort, providing life‐sustaining treatments often requiring the skills of all three off these specialties. Interestingly, of the three, only the practice of radiation oncology has an inherent handicap compared with the other two. Whereas surgeons and medical oncologists can pick up a new technique or drug overnight, or discard one just as quickly, a new radiation source places a heavy financial burden on the hospital in the form of multi‐million dollar investment in an accelerator and a heavily shielded treatment room. Perforce, these are long‐term investments because a well‐maintained accelerator can function for generations, and a shielded treatment room, if given the time, might outlast the pyramids.

Regardless of the radiation source, 20 years from now, and short of help from synergistic drugs, radiation treatments are likely to be delivered in much the same way as they are today, and with similar results. But what is far more likely is that medical oncologists will have an increasing number of more effective drugs at their disposal, and that many of these drugs will compete with radiation therapy. This scenario accepted, it would make sense, both medically and economically, to maintain but not enlarge, our current armamentarium of several thousand Linacs and thirty‐odd PBT systems to treat the diminishing number of patients whose cancers remain refractory to drugs. As for PBT, without supporting evidence that shows significant increases in survival times, money spent on these and other new exotic radiation sources will be money taken away from far more critical general medical and hospital requirements.

自1930年代开发出一百万伏特X射线机和200伏特X射线机以来，它不仅减少了皮肤红斑和骨坏死，而且还增加了深度剂量，所以医学物理学家一直在努力开发放射源和放射线。提高大多数实体瘤治疗率的技术。这项研究的主要结果之一是线性电子加速器（Linac）在4–10 MeV范围内工作。从本世纪中叶开始，这些机器成为并且仍然是放射治疗的主要工具。他们以可接受的成本可靠地执行任务，并通过巧妙设计的辅助设备可以治疗各种解剖部位。

现在，经过一个世纪的研究和开发，以及引入越来越复杂和昂贵的放射源，看来放射治疗作为癌症治疗的功效已达到平稳状态。例如，质子束疗法（PBT）为治疗计划提供了更高的治疗比率，这可能会降低放射毒性，但是缺乏PBT为患者提供更长生存时间的证据。Mayo诊所网站的以下段落简要总结了PBT的当前状态：

质子疗法在治疗多种癌症方面显示出了希望。研究表明，质子疗法可能比传统放射产生更少的副作用，因为医生可以更好地控制质子束在何处沉积能量。但是很少有研究直接比较质子疗法的放射线和X射线辐射，因此尚不清楚质子疗法是否对延长寿命更有效。”

显然，与X射线相比，PBT的存活时间和毒性水平差异可能很小。因此，要获得统计上有效的比较，将需要长期研究相对大量的患者，并且需要采用随机前瞻性临床试验（RPCT）的方法。考虑到进行此类试验的后勤工作，放射治疗中的此类试验很少而且相差不大也就不足为奇了。（也许是由美国国家癌症研究所资助的针对特定癌症的质子与X射线多机构RPCT治疗有助于解决该问题。）与此同时，人性本质就是如此，使用PBT的肿瘤学家可能会真诚地相信：他的病人比过去用X射线治疗的病人做得更好，他可能已经推广了几年的新机器？

因此，在这里，与所谓的“万恶之王” ^1相比，这种疾病的最终治愈可能来自大学和大型制药实验室进行的生物学研究。在我们等待时，尽管很不耐烦，但外科医生，医学肿瘤学家和放射肿瘤学家握住了堡垒，提供维持生命的治疗通常需要这三个专业的全部技能。有趣的是，在这三种方法中，只有放射肿瘤学实践与其他两种方法相比具有固有的障碍。外科医生和肿瘤内科医生可以在一夜之间掌握新技术或新药或以同样快的速度丢弃一个新的放射源，以数百万美元的价格购买加速器和高度屏蔽的治疗室，给医院带来沉重的财务负担。对于Perforce，这是一项长期投资，因为维护良好的加速器可以世代相传，并且如果有时间的话，屏蔽的治疗室可能会比金字塔更持久。

不管从20年后开始的辐射源如何，而且由于缺乏协同药物的帮助，辐射治疗的交付方式可能与今天基本相同，而且效果相似。但是，更有可能的是，医学肿瘤学家将拥有越来越多的更有效的药物可供使用，而且其中许多药物将与放射疗法竞争。这种情况在医学和经济上都可以接受，从医学上和经济上来讲，维持但不扩大我们目前的数千个直线加速器和三十多个PBT系统的军备库，以治疗数量不断减少的癌症，这些患者仍然对药物难以治疗。至于PBT，如果没有支持证据表明生存时间显着增加，