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Microplanar beams[1] is thought to have a potential to use for novel radiotherapy of cancer, however, the radiobiological responses are not well known.
We obtained a microplanar beam at Spring-8, JASRI (Japan Synchrotron Radiation Research Institute). A multi-slit block having ten 25 µm slits every 200 µm was installed in the beam line. Irradiation was performed with the dose rate and exposure time. Average dose including peak and bottom in a whole exposure area was measured by an ionization chamber. Tumor-transplanted or hair-depilated C3H mice were irradiated to the microplanar beam for tumor growth delay (TGD) or skin reaction score (SRS) experiments. The transplantation and the depilation were performed 8 days before irradiation at home laboratory and shipped to JASRI few days before experiments. Mice were kept on a board under anesthesia, and an area of 10x20 mm2 including the tumor or the depilated skin were irradiated. Daily measurements were performed at Kitasato University.
Differences in the days to be 5 times bigger the size between each irradiated and unirradiated mice were defined as TGD time, and TGD10 express 10 days delay. Maximum skin score is defined to be 5, and SRS2.5 corresponds severe dry desquamation. These results were compared to those by γ-rays[2]. Resulting from the ratio of the doses, 3.07 (SRS2.5=169/55) times higher dose was required to give the same skin damage, hence only 2.53 (TGD10=144/57) times higher dose could show the same tumor suppression. Only a small advantage as therapeutic gain (1.21=3.07/2.53) was observed for acute microplanar beam than fractionated γ-rays in this experimental system.
\nKeywords: microplanar beam; white X-rays; growth delay; skin reaction;
\nREFERENCES
1.Dilmanian FA, Zhong Z, Bacarian T et al. Interlaced x-ray microplanar beams: A radiosurgery approach with clinical potential. (2006) Proc Natl Acad Sci USA 103; 9709-14.
2.Ando K, Koike S, Uzawa A et al. Biological gain of carbon-ion radiotherapy for the early response of tumor growth delay and against early response of skin reaction in mice. (2005) J Radiat Res 46; 51-7.
会議概要（会議名, 開催地, 会期, 主催者等）
The 12 th International Workshop on Microbeam Probes of Cellular Radiation Response
Tumor Growth and Skin Reaction in Mice by Synchrotron Microplanar Beam
