Enhanced biological effect induced by a radioactive 9C-ion beam at the depths around its Bragg peak

To explore the potential of double irradiation source, radioactive 9C-ion beam, in tumor therapy, a comparative study on the surviving effect of human salivary gland cells at different penetration depths between 9C and 12C-ion beams has been carried out. The 9C-ion beam came out more efficient in cell killing at the depths around its Bragg peak than the 12C beam, especially at the distal side of the Bragg peak. Compared to the 12C beam, an increase in RBE by a factor of up to 2.13 has been observed at the depths distal to the Bragg peak of the 9C beam. The 9C beam showed an enhanced biological effect at the penetration depths around its Bragg peak, corresponding to the stopping region of the incident 9C-ions and where the delayed low-energy particles were emitted. Further analysis revealed that cell lethality by the emitted particles from the stopping 9C-ions is responsible for the excessive biological effect at the penetration depths around the Bragg peak of the 9C beam.