20. Relative Biological Effectiveness of the 235 MeV Proton Beams at the
National Cancer Center Hospital East
Koichi Ando, Yoshiya Furusawa, Masao Suzuki, Kumie Nojima, Hideyuki
Majima, Sachiko Koike, Mizuho Aoki, Wakako Shimizu, Yasuyuki Futami, Takashi Ogino,
Shigeyuki Murayama, and Hiroshi Ikeda
Keywords: relative biological effectiveness, human,
mouse, cell survival, crypt
A therapy-dedicated cyclotron was installed in the National Cancer Center Hospital
East (NCCHE) at Kashiwa in 1997. Prior to the start of clinical use, we investigated
the biological effectiveness of therapeutic proton beams for cell lethality. The
proton beams accelerated up to 235 MeV were horizontally extracted from the cyclotron,
and scattered by a bar-ridge filter to produce a Spread-Out-Bragg-Peak (SOBP)
of 10-cm width. The biological systems used here were mouse intestinal crypt cells
and three in vitro cell lines, including SCC61 human squamous cell carcinoma,
NB1RGB human fibroblasts and V79 Chinese hamster cells. The dose responses after
irradiation at either the entrance plateau or the middle portion of SOBP were
compared with those after linac 6 MV X-ray irradiation. The fit of a linear quadratic
model to survival curves showed that proton irradiation increased the
value of SCC61 and the 
value of V79 cells with a least change for /
ratio of NB1RGB cells. The isoeffect dose that reduced either cell survivals to
10% or mouse jejunum crypts to 10 per circumference was termed D10. The relative
biological effectiveness (RBE) of protons obtained by comparing the D10 values
between protons and X-rays ranged from 0.9 to 1.2. The depth distribution of cell
lethality was measured by replating V79 cells after irradiation from a "cell stack
chamber" that received a single dose of 7 Gy at the middle position of the SOBP.
The thus-obtained cell survivals at various depths coincided well with the estimated
survivals, but tended to decrease at the distal end of the SOBP. We concluded
that an RBE of 1.1 would be appropriate for 235 MeV proton beams at the NCCHE.
Publication:
Ando, K., Furusawa, Y., Suzuki, M., Nojima, K., Majima, H., Koike, S., Aoki, M.,
Shimizu, W., Futami, Y., Ogino, Y., Murayama, S. and Ikeda, H.: J.Radiat.Res.
42, 79-89, 2001
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