[en] The aim of this study is to introduce the possibility of proton therapy. Proton therapy is one form of 'hadron therapy'. The major advantages of high energy protons and other heavy charged particles are: some particle radiation (e.g. neutrons, α-particles or ions) have a high LET; high LET radiations are biologically more effective per gray than low LET radiation; proton beams provide the best improvement in dose distribution; the differential radiosensitivity due to cell cycle position is considerably reduced with high LET radiations. The high LET radiations are clinically useful in following cases: large tumors volume, X-ray radioresistant tumors, slowly growing tumors and some advanced cancers that contain a high proton of hypoxic cell. (authors)