Yukari Yoshida1, Koichi Ando2, Ken Ando3, Kazutoshi Murata3, Yuya Yoshimoto3, Atsushi Musha2, Nobuteru Kubo3, Hidemasa Kawamura3, Sachiko Koike4, Akiko Uzawa4, Takeo Takahashi5, Tatsuya Ohno2, Takashi Nakano6. 1. Gunma University Heavy Ion Medical Center, Maebashi, Japan. Electronic address: yyukari@gunma-u.ac.jp. 2. Gunma University Heavy Ion Medical Center, Maebashi, Japan. 3. Department of Radiation Oncology, Gunma University Graduate School of Medicine, Maebashi, Japan. 4. Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Chiba, Japan. 5. Department of Radiation Oncology, Saitama Medical Center, Saitama Medical University, Kawagoe, Japan. 6. Gunma University Heavy Ion Medical Center, Maebashi, Japan; Department of Radiation Oncology, Gunma University Graduate School of Medicine, Maebashi, Japan.
Abstract
BACKGROUND AND PURPOSE: The aim of the study was to evaluate the therapeutic gain of carbon ion (C-ion) radiotherapy using a mouse model. MATERIALS AND METHODS: Transplanted fibrosarcoma (NFSa) growing in C3H/He mice and murine small intestine were irradiated with 290 MeV/nucleon C-ion beams (C-ions) in 1-12 fractions separated by 4h. The cell killing efficiencies of C-ions were measured using jejunum crypt survival and tumor growth delay (TGD) assays. RESULTS: The equieffect dose for crypt survival and TGD increased with increasing number of fractions after X-rays and 20 keV/μm C-ions, whereas TGD after 77 keV/μm C-ions rather decreased. Crypts showed stronger LET-dependent increase in α terms than the tumor while β terms less depended on LET irrespective of tissues. Therapeutic gain factor, i.e., a ratio of tumor RBE over crypt RBE, of 77 keV/μm C-ions was more than unity at any doses while that of 20 keV/μm C-ions increased with an increase in dose per fraction. CONCLUSIONS: These specific data imply that use of large dose per fraction would be suitable for C-ion radiotherapy irrespective of LET from the point of view of therapeutic gain, though small dose per fraction by high-LET radiation decreases total dose for tumor.
BACKGROUND AND PURPOSE: The aim of the study was to evaluate the therapeutic gain of carbon ion (C-ion) radiotherapy using a mouse model. MATERIALS AND METHODS:Transplanted fibrosarcoma (NFSa) growing in C3H/He mice and murine small intestine were irradiated with 290 MeV/nucleon C-ion beams (C-ions) in 1-12 fractions separated by 4h. The cell killing efficiencies of C-ions were measured using jejunum crypt survival and tumor growth delay (TGD) assays. RESULTS: The equieffect dose for crypt survival and TGD increased with increasing number of fractions after X-rays and 20 keV/μm C-ions, whereas TGD after 77 keV/μm C-ions rather decreased. Crypts showed stronger LET-dependent increase in α terms than the tumor while β terms less depended on LET irrespective of tissues. Therapeutic gain factor, i.e., a ratio of tumor RBE over crypt RBE, of 77 keV/μm C-ions was more than unity at any doses while that of 20 keV/μm C-ions increased with an increase in dose per fraction. CONCLUSIONS: These specific data imply that use of large dose per fraction would be suitable for C-ion radiotherapy irrespective of LET from the point of view of therapeutic gain, though small dose per fraction by high-LET radiation decreases total dose for tumor.