FAQ
Radiotherapy is a cancer treatment with a long history that can be traced back to a century ago. As the name suggests, radiotherapy uses radiation to cause destruction of cancer cells, thus achieving its therapeutic effects. What is called radiation is actually a large family of electromagnetic waves and particles with different properties (X-rays, γ rays, electrons, protons, neutrons, carbon nuclei, etc.). However, despite innumerable types of radiation, the vast majority of the world’s hospitals only employ X-rays in radiotherapy, being constrained by physical properties, machinery and equipment, and many practical considerations.
“Diàn liáo” is a commonly heard nickname for radiotherapy. This is mainly because X-rays are referred to as “tiān-kong,” (“electrical rays”) in Taiwanese. As mentioned earlier, the majority of contemporary radiotherapy uses X-rays to treat patients. It is because of this that radiotherapy has acquired the unique moniker of “diàn liáo” in Taiwan. When you hear about “diàn liáo” during the course of cancer treatment, it essentially refers to radiotherapy.
Note：The linear accelerator that can be used in X-ray treatments can often utilize electrons for treatment as well. However, due to limitations from their physical properties, electrons are restricted to use in superficial tumors in clinical usage, and their clinical applications are far less extensive than those of X-rays and protons.
What is called radiation is actually a large family of electromagnetic waves and particles with different properties (X-rays, rays, electrons, protons, neutrons, carbon nuclei, etc.). Of all the different types of radiation, X-rays, being comparatively easy to generate and manipulate, have become the mainstream of modern radiotherapy. From a physical standpoint, X-rays may be regarded as comprising many microparticles known as photons, X-ray therapy is also known as photon therapy.
In a nutshell, radiotherapy can be performed using many different types of radiation, and photon therapy are the most commonly used type of radiotherapy in the world right now—X-ray therapy.
In contrast to the commonly seen photon therapy, only a few radiotherapy centers in the world are capable of using protons for treating cancer. The greatest problem with photon therapy is its “inability to brake.” Once X-rays inflict damage on the tumor, it continues to pass through the tumor and injures the healthy tissue behind the tumor. Even if modern radiotherapy has greatly increased the accuracy of radiotherapy, unnecessary radiation exposure beyond these treatment regions remains an inevitable “original sin” of photon therapy.
Differing from photon therapy, proton therapy has the physical feature of the Bragg peak. After a proton enters the body, it acts like a depth charge, releasing its energy all at once only after the beam reaches a certain depth in the body. The healthy tissue behind the tumor will not be exposed to additional radiation, thus reducing the side effects potentially arising from radiotherapy. When side effects diminish, the most direct effect is an improvement in the patient’s quality of life.
The question that comes up most frequently in proton therapy is whether its efficacy is superior to photon therapy. This is actually a highly complicated issue. The simplest answer is that the two are similar in lethality. There should be no difference between photons and protons in terms of tumor control probability. Notably, however, as proton therapy diminishes injury to healthy tissue, we have the opportunity to increase treatment intensity while holding the intensity of side effects constant. In other words, proton therapy opens doors to previously untreatable cancers. The most prominent example is advanced localized liver cancer.
However, proton therapy is not a panacea entirely free of flaws. The difficulty levels of applying photons and protons to the same treatment is comparable to the difference between riding a bicycle and driving a volumetric concrete mixer. In contrast to photons, protons are particles that carry electric charge and have mass. Therefore, proton therapy requires coordination with expensive and precise equipment to provide treatment. This brings the first and perhaps most obvious problem of proton therapy—high treatment expenses. Other than financial issues, the sensitivity of proton therapy to tumor location and depth also poses a challenge to physicians and radiation technologists . As a result, proton therapy is not a suitable treatment option for patients who cannot lie still for long periods or do not have stable vital signs.
All in all, proton therapy is a radiotherapeutic option with considerable potential, but selection of the right patients and design of the most appropriate treatment plan for a cure continue to challenge the knowledge and experience of physicians, physicists, and radiation technologists.