title: Evaluation of SCCVII tumor cell survival in clamped and non-clamped solid tumors exposed to carbon-ion beams in comparison to X-rays.
abstract: The aim of this study was to measure the RBE (relative biological effectiveness) and OER (oxygen enhancement ratio) for survival of cells within implanted solid tumors following exposure to 290MeV/nucleon carbon-ion beams or X-rays. Squamous cell carcinoma cells (SCCVII) were transplanted into the right hind legs of syngeneic C3H male mice. Irradiation with either carbon-ion beams with a 6-cm spread-out Bragg peak (SOBP, at 46 and 80keV/μm) or X-rays was delivered to 5-mm or less diameter tumors. We defined three different oxygen statuses of the irradiated cells. Hypoxic and normoxic conditions in tumors were produced by clamping or not clamping the leg to avoid blood flow. Furthermore, single-cell suspensions were prepared from non-irradiated tumors and directly used to determine the radiation response of aerobic cells. Single-cell suspensions (aerobic condition) were fully air-saturated. Single-cell suspensions were prepared from excised and trypsinized tumors, and were used for in vivo-in vitro colony formation assays to obtain cell survival curves. The RBE values increased with increasing LET in SOBP beams. The maximum RBE values in three different oxygen conditions; hypoxic tumor, normoxic tumor and aerobic cells, were 2.16, 1.76 and 1.66 at an LET of 80keV/μm, respectively. After X-ray irradiation the OERh/n values (hypoxic tumor/normoxic tumor) were lower than the OERh/a (hypoxic tumor/aerobic cells), and were 1.87±0.13 and 2.52±0.11, respectively. The OER values of carbon-ion irradiated samples were small in comparison to those of X-ray irradiated samples. However, no significant changes of the OER at proximal and distal positions within the SOBP carbon-ion beams were observed. To conclude, we found that the RBE values for cell survival increased with increasing LET and that the OER values changed little with increasing LET within the SOBP carbon-ion beams.
authors.affiliation: Next Generation Medical Physics Research Program, Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Japan; Heavy-Ion Radiobiology Research Group, Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Japan. Electronic address: hirayama@nirs.go.jp.
authors.forename: Ryoichi
authors.initials: R
authors.lastname: Hirayama
authors.forename: Akiko
authors.initials: A
authors.lastname: Uzawa
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Takase
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Matsumoto
authors.forename: Miho
authors.initials: M
authors.lastname: Noguchi
authors.forename: Kana
authors.initials: K
authors.lastname: Koda
authors.forename: Masakuni
authors.initials: M
authors.lastname: Ozaki
authors.forename: Kei
authors.initials: K
authors.lastname: Yamashita
authors.forename: Huizi
authors.initials: H
authors.lastname: Li
authors.forename: Yuki
authors.initials: Y
authors.lastname: Kase
authors.forename: Naruhiro
authors.initials: N
authors.lastname: Matsufuji
authors.forename: Sachiko
authors.initials: S
authors.lastname: Koike
authors.forename: Shin-ichiro
authors.initials: S
authors.lastname: Masunaga
authors.forename: Koichi
authors.initials: K
authors.lastname: Ando
authors.forename: Ryuichi
authors.initials: R
authors.lastname: Okayasu
authors.forename: Yoshiya
authors.initials: Y
authors.lastname: Furusawa
mesh_terms: D000818:Animals; D002250:Carbon Radioisotopes / Q000009:adverse effects*; D002294:Carcinoma, Squamous Cell / Q000473:pathology* / Q000532:radiotherapy; D002470:Cell Survival; D003114:Colony-Forming Units Assay; D000860:Hypoxia / Q000473:pathology*; D018499:Linear Energy Transfer; D008297:Male; D051379:Mice; D008808:Mice, Inbred CBA; D009369:Neoplasms / Q000473:pathology* / Q000532:radiotherapy; D012062:Relative Biological Effectiveness; D014407:Tumor Cells, Cultured; D014965:X-Rays
chemical_list: D002250:Carbon Radioisotopes
keywords: Carbon-ions; Cell killing; Hypoxic fraction; OER; RBE