title: Determination of the relative biological effectiveness and oxygen enhancement ratio for micronuclei formation using high-LET radiation in solid tumor cells: An in vitro and in vivo study.
abstract: We determined the relative biological effectiveness (RBE) and oxygen enhancement ratio (OER) of micronuclei (MN) formation in clamped (hypoxic) and non-clamped (normoxic) solid tumors in mice legs following exposure to X-rays and heavy ions. Single-cell suspensions (aerobic) of non-irradiated tumors were prepared in parallel and used directly to determine the radiation response for aerobic cells. Squamous cell carcinoma (SCCVII) cells were transplanted into the right hind legs of syngeneic C3H/He male mice. Irradiation doses with either X-rays or heavy ions at a dose-averaged LET (linear energy transfer) of 14-192keV/μm were delivered to 5-mm diameter tumors and aerobic single-cells in sample-tubes. After irradiation, the tumors were excised and trypsinized to observe MN in single-cells. The single-cell suspensions were used for MN formation assays. The RBE values increased with increasing LET. The maximum RBE values for the three different oxygen conditions; hypoxic tumor, normoxic tumor, and aerobic cells, were 8.18, 5.30, and 3.76 at an LET of 192keV/μm, respectively. After X-irradiation, the OERh/n values (hypoxic tumor/normoxic tumor) were lower than the OERh/a (hypoxic tumor/aerobic cells), and were 1.73 and 2.58, respectively. We found that the OER for the in vivo studies were smaller in comparison to that for the in vitro studies. Both of the OER values at 192keV/μm were small in comparison to those of the X-ray irradiated samples. The OERh/n and OERh/a values at 192keV/μm were 1.12 and 1.19, respectively. Our results suggest that high LET radiation has a large biological effect even if a solid tumor includes substantial numbers of hypoxic cells. To conclude, we found that the RBE values under each oxygen state for non-MN fraction increased with increasing LET and that the OER values for both tumors in vivo and cells in vitro decreased with increasing LET.
authors.affiliation: Medical Physics Research Program, Research Center for Charged Particle Therapy, National Institute of Radiological Sciences (NIRS), 4-9-1 Anagawa, Inage-ku, Chiba-shi, Chiba 263-8555, Japan. Electronic address: hirayama@nirs.go.jp.
authors.forename: Ryoichi
authors.initials: R
authors.lastname: Hirayama
authors.affiliation: Medical Physics Research Program, Research Center for Charged Particle Therapy, National Institute of Radiological Sciences (NIRS), 4-9-1 Anagawa, Inage-ku, Chiba-shi, Chiba 263-8555, Japan.
authors.forename: Akiko
authors.initials: A
authors.lastname: Uzawa
authors.affiliation: Medical Physics Research Program, Research Center for Charged Particle Therapy, National Institute of Radiological Sciences (NIRS), 4-9-1 Anagawa, Inage-ku, Chiba-shi, Chiba 263-8555, Japan.
authors.forename: Maki
authors.initials: M
authors.lastname: Obara
authors.affiliation: School of Engineering, Tokai University, 1117 Kitakaname, Hiratsuka-shi, Kanagawa 259-1292, Japan.
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Takase
authors.affiliation: Medical Physics Research Program, Research Center for Charged Particle Therapy, National Institute of Radiological Sciences (NIRS), 4-9-1 Anagawa, Inage-ku, Chiba-shi, Chiba 263-8555, Japan.
authors.forename: Kana
authors.initials: K
authors.lastname: Koda
authors.affiliation: Medical Physics Research Program, Research Center for Charged Particle Therapy, National Institute of Radiological Sciences (NIRS), 4-9-1 Anagawa, Inage-ku, Chiba-shi, Chiba 263-8555, Japan.
authors.forename: Masakuni
authors.initials: M
authors.lastname: Ozaki
authors.affiliation: Advanced Science Research Center, Japan Atomic Energy Agency (JAEA), 2-4 Shirakata-Shirane, Tokai-mura, Naka-gun, Ibaraki 319-1195, Japan.
authors.forename: Miho
authors.initials: M
authors.lastname: Noguchi
authors.affiliation: Medical Physics Research Program, Research Center for Charged Particle Therapy, National Institute of Radiological Sciences (NIRS), 4-9-1 Anagawa, Inage-ku, Chiba-shi, Chiba 263-8555, Japan.
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Matsumoto
authors.affiliation: Medical Physics Research Program, Research Center for Charged Particle Therapy, National Institute of Radiological Sciences (NIRS), 4-9-1 Anagawa, Inage-ku, Chiba-shi, Chiba 263-8555, Japan.
authors.forename: Huizi
authors.initials: H
authors.lastname: Li
authors.affiliation: Medical Physics Research Program, Research Center for Charged Particle Therapy, National Institute of Radiological Sciences (NIRS), 4-9-1 Anagawa, Inage-ku, Chiba-shi, Chiba 263-8555, Japan.
authors.forename: Kei
authors.initials: K
authors.lastname: Yamashita
authors.affiliation: Medical Physics Research Program, Research Center for Charged Particle Therapy, National Institute of Radiological Sciences (NIRS), 4-9-1 Anagawa, Inage-ku, Chiba-shi, Chiba 263-8555, Japan.
authors.forename: Sachiko
authors.initials: S
authors.lastname: Koike
authors.affiliation: Heavy Ion Medical Center, Gunma University, 3-39-22 Showa-machi, Maebashi-shi, Gunma 371-8511, Japan.
authors.forename: Koichi
authors.initials: K
authors.lastname: Ando
authors.affiliation: Medical Physics Research Program, Research Center for Charged Particle Therapy, National Institute of Radiological Sciences (NIRS), 4-9-1 Anagawa, Inage-ku, Chiba-shi, Chiba 263-8555, Japan.
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Shirai
authors.affiliation: Medical Physics Research Program, Research Center for Charged Particle Therapy, National Institute of Radiological Sciences (NIRS), 4-9-1 Anagawa, Inage-ku, Chiba-shi, Chiba 263-8555, Japan.
authors.forename: Naruhiro
authors.initials: N
authors.lastname: Matsufuji
authors.affiliation: Medical Physics Research Program, Research Center for Charged Particle Therapy, National Institute of Radiological Sciences (NIRS), 4-9-1 Anagawa, Inage-ku, Chiba-shi, Chiba 263-8555, Japan.
authors.forename: Yoshiya
authors.initials: Y
authors.lastname: Furusawa
mesh_terms: D000818:Animals; D002294:Carcinoma, Squamous Cell / Q000235:genetics* / Q000378:metabolism*; D045744:Cell Line, Tumor; D004307:Dose-Response Relationship, Radiation; D020450:Heavy Ions; D066298:In Vitro Techniques; D018499:Linear Energy Transfer; D008297:Male; D051379:Mice; D008809:Mice, Inbred C3H; D048629:Micronuclei, Chromosome-Defective / Q000528:radiation effects*; D015162:Micronucleus Tests; D009368:Neoplasm Transplantation; D010101:Oxygen Consumption / Q000528:radiation effects*; D012062:Relative Biological Effectiveness; D014965:X-Rays
keywords: High LET radiation; In vivo solid tumor; Micronucleus formation; OER: oxygen enhancement ratio; RBE: relative biological effectiveness