What Are the Pros and Cons of Proton Therapy for Cancer?

Protons are stable elementary particles with a charge of 1.602 19 × 10-19C, a static mass of 1.672 61 × 10-27kg, and the proton energy range for radiotherapy is 50-250eMeV.

Protons are stable elementary particles with a charge of 1.602 19 × 10-19C, a static mass of 1.672 61 × 10-27kg, and the proton energy range for radiotherapy is 50-250eMeV.

Proton therapy proton concept

The so-called protons are particles with a positive charge after the hydrogen atom strips the electron.

Proton therapy concept of proton radiation

The hydrogen atom is accelerated by the high energy of the accelerator and becomes a strong penetrating ionizing radiation. This is the proton radiation.

Proton therapy tumors

Proton therapy is a type of radiation therapy. After the protons enter the human body, a sharp dose peak is formed at the end of the range, which is called the Bragg peak. By adjusting the energy to broaden the Bragg peak, the Bragg peak can cover the tumor. In addition, the energy loss of the proton incident channel is small, and the side scattering is also small. The dose received by normal tissues before, after, and around is small, so it has good radiophysics performance.

Protons, electrons, and photons are all low-LET radiation. The radiobiological properties are related to the following parameters: ^[1]

1. Oxygen enhancement ratio (OER) is the ratio of the dose needed for itchy cells and oxygen-enriched cells to produce the same degree of biological effect. It describes the dependence of the radiosensitivity of this type of radiation on the oxygen content of the cells.

2. Relative biological effectiveness (RBE) is the ratio of the dose required for this kind of radiation to the dose required for gamma radiation of Co when the same degree of biological effect is produced.

3. Linear energy transfer (LET) is the ionization density along the unit track length of the secondary particle, and its unit is KeV / . When LET is lower than 10KeV / , OER and RBE are almost unchanged, OER is high, and RBE is low. When LET is higher than 10KeV / , OER starts to decrease and RBE gradually rises. Therefore, below 10KeV / is called low LET radiation, and above is high LET radiation.

In proton therapy, special machines and appliances can be used to combine the depth of the Bragg peak with the shape of the patient's different lesions. Therefore, the dose can be concentrated, only the lesion is targeted for irradiation, and the impact on normal tissues is reduced.

The special instruments used for proton beam irradiation are collimators and conformers. With reference to CT images, they are designed using a dedicated computer system, and 1 to 3 sets of instruments are developed for each patient according to the irradiation direction.