X-ray and gamma-ray which are forms of photons (electromagnetic waves) cannot be stopped but pass completely through the human body.
However, proton beam (generated from nucleus of hydrogen) is accelerated to the speed of light to travel the human body to a certain depth without losing energy and then stops transmitting energy to the surrounding tissues while the proton kinetic energy decreases to zero.
It is so-called “Bragg Peak”, a physical property of proton bean therapy. If the “Bragg Peak” can be created and set at the tumor site, it is possible to minimize unnecessary radiation dose to the area from the body surface to the tumor site in comparison with x-ray therapy. Another advantage of “Bragg Peak” is the fact that there is no irradiation damage to normal tissues at the posterior surface of the tumor mass.
Why radiation therapy possesses the capacity to inactivate cancers? In fact, the effect of radiation therapy is not to burn cancers with the power of radiation (even 0.1 °C temperature rise will not happen) and not a surgical scalpel to cut off tumors (painlessness). The effect of radiation therapy is to kill tumor cells by damaging genetic material (DNA).
X-ray is regarded as low LET (Linear Energy Transfer) radiation, whereas proton beam which belongs to particle beams is medium LET radiation.
Particle beams are most likely to hurt the DNA double helix in tumor cells with strong lethality so tumor cells are not easily revived. In comparison with the damage caused by X-ray, it is more effective to treat intractable cancers than other conventional radiation therapies.
Clinical Cases for Proton Bean Therapy
Locally invasive in-operable pancreatic body cancer (cT4N1M0/stage IVa). Combinations of proton beam therapy and chemotherapy were conducted. Shrinkage in cancer mass was observed on CT taken after 6 years and 4 months post-treatment. The patient is alive and well.
Hepatic cancer with some 10 cm diameter (Child-Pugh Classification A). Proton beam therapy was conducted. Shrinkage in cancer mass was observed on CT taken after 2 years and 6 months post-treatment. The patient is alive and well.
Physical Statistics of Proton Beam Therapy Treatment
During October 2018 to April 2020, a total number of cancer patients treated by proton beam therapy has reached 5,406 since the grand opening of Proton Therapy Center in Oct. 2008. Cancers of head & neck, lung, prostate, esophagus, liver and pancreas are predominantly treated.