The biological mechanism of killing tumor cells by gamma rays produced by radioactive particles is mainly the direct action of high linear energy transfer (LET) rays on DNA molecules of tumor cells to make the chain of DNA molecules single-strand break, double-bond break and lose the ability to reproduce, so as to achieve a more complete therapeutic effect. The main advantages compared with external radiotherapy: (1) Although external radiotherapy equipment is advancing rapidly, the treatment of intrathoracic malignant tumors that move up and down by breathing still has the defect of uneven radiation dose, and the intensity of its radiation source is too large, which causes more obvious complications to the patient’s body; while the particles of “particle knife” are directly planted in the tumor. The radiation dose is uniform and not affected by the activity, and it rarely damages the normal tissue. (2) External radiotherapy cannot avoid the shortcomings of short-time fractionation. The fractional short-time irradiation of external radiotherapy can only treat cells in one part of the tumor reproduction cycle. After the end of irradiation, the tumor cells in other phases can still recover their reproductive ability soon. The tumor cells can be stimulated by any stimulation to change from quiescent cells to active cells, and the cell multiplication time is significantly shortened, so they can still grow rapidly in the interval between irradiation sessions, which directly affects the therapeutic effect of external radiotherapy. In contrast, the particles of “particle knife” can effectively irradiate tumor cells in the tumor for up to 180 days, which can kill all tumor cells.