Particle Beam may have Higher Effectiveness in Treating Chemo-resistant Cancers than Low-LET Photon Beam Therapy.

It is now well-established that outcomes of radiotherapy depend on quality of radiation. A large body of experimental evidences suggests that high-LET (linear energy transfer) radiation or particle radiation has the ability to kill tumor cells more efficiently than low-LET photon beams such as X-rays and γ-rays [1,2]. The unique characteristics of particle beam, which includes precise dose distribution, formation of complex and “clustered” DNA damage in target cells, capacity to kill cells with equal effectiveness irrespective of their cell cycle stage and oxygen content, ability to cause biological damage by direct action, and inverse dosedepth relation are considered to be responsible for higher relative biological effectiveness (RBE) than low-LET photon beams. However, the efficacy of particle radiation in killing chemo-resistant cells compared to low-LET radiation is not well-documented.