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