title: Enhanced efficiency in cell killing at the penetration depths around the Bragg peak of a radioactive 9C-ion beam.
abstract: OBJECTIVE
  To evaluate the potential importance of radioactive 9C-ion beam in cancer radiotherapy.
  
  
  METHODS
  Human salivary gland (HSG) cells were exposed to a double-radiation-source 9C beam at different depths around the Bragg peak. Cell survival fraction was determined by standard clonogenic assay. For comparison, the same experiment was conducted for a therapeutic 12C beam. To determine relative biologic effectiveness (RBE) values, HSG cells were also irradiated with 60Co gamma-rays of fractionation scheme as the reference.
  
  
  RESULTS
  The 9C beam was more efficient in cell killing at the depths around its Bragg peak than was the 12C beam, which corresponded to the 9C-ion stopping region and where delayed low-energy particles were emitted. The RBE value at 50% survival level for the 9C beam varied from 1.38 to 4.23. Compared with the 12C beam, the RBE values for the 9C beam were always higher; an increase in RBE by a factor of up to 1.87 has been observed at the depths distal to the Bragg peak.
  
  
  CONCLUSIONS
  The potential advantage of radioactive 9C-ion beam in cancer therapy has been revealed at low dose rate in comparison with a therapeutic 12C beam. This observation, however, remains to be investigated at therapeutic dose rates in the future.
authors.affiliation: Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou, China.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Li
authors.forename: Yoshiya
authors.initials: Y
authors.lastname: Furusawa
authors.forename: Mitsutaka
authors.initials: M
authors.lastname: Kanazawa
authors.forename: Tatsuaki
authors.initials: T
authors.lastname: Kanai
authors.forename: Atsushi
authors.initials: A
authors.lastname: Kitagawa
authors.forename: Mizuho
authors.initials: M
authors.lastname: Aoki
authors.forename: Eriko
authors.initials: E
authors.lastname: Urakabe
authors.forename: Takehiro
authors.initials: T
authors.lastname: Tomitani
authors.forename: Shinji
authors.initials: S
authors.lastname: Sato
authors.forename: Mitsuo
authors.initials: M
authors.lastname: Yoshimoto
authors.forename: Zengquan
authors.initials: Z
authors.lastname: Wei
mesh_terms: D002244:Carbon / Q000627:therapeutic use; D002250:Carbon Radioisotopes / Q000627:therapeutic use*; D002470:Cell Survival / Q000528:radiation effects; D006801:Humans; D012062:Relative Biological Effectiveness; D012469:Salivary Glands / Q000166:cytology / Q000528:radiation effects*
chemical_list: D002250:Carbon Radioisotopes; D002244:Carbon