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Introduction to proton therapy

The principle of radiation therapy is to useα, β, γ rays and X-rays, electron beams, proton beams and other particle beams produced by various X-ray treatment machines or accelerators to treat malignant tumors. Traditional radiotherapy, due to the nature of the radiation itself, causes the radiation to kill cancer cells while also causing damage to normal cells during the treatment process, which causes the patient to produce toxic side effects after radiotherapy; in addition, in order to reduce radiotherapy Damage to normal tissues, to a certain extent, the dose of radiotherapy is also limited, which affects the efficacy of tumor treatment.

Proton therapy is a new technology that utilizes the unique characteristics of the proton beam"Bragg Peak" to treat tumors. After the proton is accelerated to about two-thirds of the speed of light by the synchrotron, it irradiates the tumor tissue and directly attacks the cancer cell, cutting off the two DNA strands in the cancer cell nucleus, making the damaged cancer cell irreparable. Proton is a positively charged subatomic particle. Due to the superior physical dose distribution of the proton beam, the radiation dose can be concentrated to the tumor site. Therefore, compared with traditional radiotherapy, proton therapy has incomparable advantages.

  • Proton beam and X-ray radiation dose distribution
  • Proton beam and X-ray penetration in the body
How is proton therapy implemented?

Proton therapy is an advanced radiotherapy technique that uses proton therapy to kill cancer cells. Protons come from an ion source. In less than one second, hydrogen atoms are separated into negatively charged electrons and positively charged protons. The protons are then injected into the cyclotron to be accelerated (Figure 3, Figure 4), and accelerate to At 70% of the speed of light, these accelerated protons with high energy enter the energy selection system composed of magnets (Figure 5). According to the depth of the patient's tumor, protons with different energies that can meet the needs of treatment are selected, and then the protons pass through the transmission system (Figure 6) Enter the treatment room through the rotating frame. When the proton passes through the gantry, the proton beam is shaped by the collimator and then irradiated to the depth of the tumor. The gantry can freely rotate 360 degrees, so the patient can be treated at any angle (Figure 7). The patient positioning is highly accurate. Our proton therapy gantry is equipped with CBCT. CT scans are performed before each treatment to confirm the correct positioning. At the same time, pen-beam scanning is also implemented (Figure 8), scanning one point by one point. , Scanning layer by layer, the shape of the treatment can be highly matched with the shape of the tumor.

  • Figure 3
  • Figure 4
  • Figure 5
  • Figure 6
  • Figure 7
  • Figure 8
Three advantages of proton therapy
1. Accurately kill tumors

In traditional radiotherapy, the energy of the rays is gradually attenuated, and the effective energy to reach the affected area is limited; while the proton beam has the characteristic of "Bragg Peak", and the energy release reaches the maximum at a certain point. Using this characteristic, it can make it in the diseased area. The specific part releases the maximum energy to achieve the best therapeutic effect. That is to say, when traditional rays reach deep tumors, they are at the end of their lives, but proton beams can "deep into the enemy's camp" to achieve "stereotactic blasting." At the same time, because the particles of the high-energy proton beam are small and concentrated in mass, they are less scattered in the human body, reducing the radiation dose to the surrounding normal tissues, thereby improving the accuracy of tumor treatment.

2. Protect normal organizations

While accurately and effectively killing tumor tissues, proton radiotherapy can also minimize the damage caused by radiotherapy to normal tissues. The range of X-rays or γ-rays used in traditional radiotherapy (photon therapy) cannot be controlled. In addition to the irradiation of tumor cells, normal tissues in front and behind the tumor will also be irradiated, resulting in side effects of radiotherapy; while proton therapy is due to the "Bragg Peak" With the existence of ", the energy is concentratedly released. The tissue in front of the tumor receives only a very small amount of radiation, while the normal tissue behind and on the side of the tumor receives almost zero radiation, which can effectively protect the normal tissues of the human body and greatly reduce the toxic and side effects of radiotherapy. For example, in the treatment of left breast cancer, proton therapy protects the adjacent heart and lung tissues (Figure 9); in the radiotherapy of head and neck tumors, proton therapy shows its advantages, such as brain stem, eyes, mouth, and parotid glands. It is well protected, and the occurrence of complications and sequelae is greatly reduced (Figure 10).

  • Figure 9. Comparison of proton therapy and photon therapy for breast cancer
  • Figure 10. Comparison of proton therapy and photon therapy for head and neck tumors
3. Wide application and high safety

As the newest and most promising member of tumor treatment methods, proton therapy has comprehensive and expanding technical advantages. Based on the pencil beam scanning technology, proton intensity-modulated radiotherapy has a wider applicability than other treatment methods (Figure 11), especially in the field where photon therapy is incapable of showing great advantages. Proton therapy has played an irreplaceable role in the treatment of ocular tumors, large deep tumors, and tumors that are not sensitive to conventional radiation (photon rays, X-rays, electron rays, and gamma rays). Proton therapy also has unparalleled advantages in childhood tumors and head and neck tumors.

Although proton therapy has only become popular in China in recent years, its substance therapy was first proposed in 1946. In 1988, proton therapy was approved by the U.S. FDA, and since then it has shined in the field of tumor treatment. At present, there are nearly 30 proton therapy centers in the United States, including Mayo Hospital, University of Florida Proton Center, MD Anderson Cancer Center, and Massachusetts General Hospital Cancer Center. More than 220,000 patients worldwide have received proton therapy, so proton therapy is a mature and safe radiotherapy technology.

The process of proton therapy
  • 1
    Fixed position
  • 2
    CT/MRI scan positioning
  • 3
    Delineate the target area and design the radiotherapy plan
  • 4
    Radiotherapy plan verification
  • 5
    Give radiotherapy
Typical case of proton therapy
Central Nervous System Tumors
Head and neck tumors (nasopharyngeal cancer)
Esophageal cancer
Breast cancer
Lung cancer
Liver cancer
Pancreatic cancer
Pancreatic cancer
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