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Radiother Oncol. 2015 Nov;117(2):351-7. doi: 10.1016/j.radonc.2015.09.027. Epub 2015 Oct 8.

Evaluation of therapeutic gain for fractionated carbon-ion radiotherapy using the tumor growth delay and crypt survival assays.

Author information

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.

KEYWORDS:

Carbon-ion beam; Crypt; Fraction; RBE; Survival parameters; Tumor growth delay

PMID:
26454348
DOI:
10.1016/j.radonc.2015.09.027
[Indexed for MEDLINE]

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