Proton therapy is a form of radiotherapy used for cancer (generic term for malignant tumors, sarcomas, etc.) treatment. You may think about X-rays and gamma rays when it comes to radioactive rays, but it is a proton beam that replaces them to be used for this therapy. Detailed information about what a proton beam is and why it is good for cancer treatment is given below.
A proton is an atomic nucleus of hydrogen, and a particle positively charged. It is produced with hydrogen gas as the source reagent, by separating electrons from the nucleus in the high-temperature plasma state. When massive protons are accelerated in vacuum all at once, a proton beam, of which the penetrative power into a human body is strong enough to destroy cancerous cells, is produced. The special equipment used for this process is called an accelerator. The speed of protons in the accelerator comes close to 70% of the speed of light.
In the above explanation, it says that “a proton beam has the strong penetrative power into a human body.” However, it is not the one and only feature of a proton beam. It has “charged particle radiation,” which suits cancer treatment because of the reasons explained as follows.
When the power of a proton beam reaches to maintain a certain level of energy, the protons penetrate a human body at the uniform speed and stop completely at a designated depth. Therefore, a proton beam does not go any deeper to damage normal cells. The depth is controllable and can be adjusted. Furthermore, most of the energy distribution of protons focuses just before they stop. In other words, the amount of radiation irradiated in the form of a proton beam is used quite effectively at a designated depth. Please see the figure below for details.
As you see in the figure, the majority of X-ray and gamma ray radiations is absorbed near the body surface, and the amount of radiation energy becomes rather small as they go deep inside the body. On the other hand, the radiation energy of a proton beam peaks deep inside the body (namely where the tumor is). Proton therapy optimally exploits this feature.
Depth Dose Curve
As explained above, positions where protons come to stop deep inside the body can be fully controlled by adjusting the energy. Because of this feature, a proton beam can zero in on cancer cells and destroy them. In addition, there is a special device that controls the peak time of irradiation, which makes it possible to deliver high dose of radiation for precisely desired duration. Therefore, however thick the tumor can be, it will be targeted and destroyed. Thus, maximum energy of the dose can be focused only to the targeted spot quite effectively. This is the major reason why a proton beam is used for the therapy. Here are the merits of proton therapy for cancer patients.
Proton beams can be irradiated with surgical precision, delivering maximum energy to the designated cancer lesion, which allows them to destroy only cancer cells intensively.
Because of the ability of precisely targeting tumors, proton beams can be a safer choice when tumors are near sensitive organs than conventional radiations.
As the irradiation volume to surrounding healthy cells are significantly small, they receive only a little injury, which makes it easy for patients to undergo cancer treatments with fewer harmful side effects.
With these merits, proton therapy can be easily applied even to elderly patients. In addition, it is expected that patients can go back into society soon enough to maintain quality of life after the treatment.
