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The Optimum Conditions in the Analysis of Boron
Micro-Distribution in Tumor Cells
Using PIXE and PIGE
K. Endo a) , Y. Shibata a) , T. Yamamoto a) , K. Nakai a) , A. Matsumura a) , T. Satoh b) ,
A. Yokoyama b) , M. Kohka b) , T. Ohkubo b) , A. Yamazaki b) , Y. Ishii b) ,
T. Kamiya b) and K. Ishii c)
a) Department of Neurosurgery, Institute of Clinical Medicine, University of Tsukuba, b) Department of
Advanced Radiation Technology, TARRI, JAEA, c) School of Engineering, Tohoku University
Micro particle-induced X-ray emission (micro-PIXE)
was applied to determine the inter- and intracellular
distribution of boron-10( 10 B) in tumor cells. Because the
energy of micro-PIXE from 10 B is too low, particle-induced
gamma-ray emission (PIGE) was employed to detect the
gamma-rays produced from the nuclear reaction of
10 7
B (p, γ) Be.
Cultured 9L gliosarcoma cells grown on polycarbonate
film were exposed to sodium borocaptate (BSH). To
analyze the inter- and intra-cellular distribution of 10 B in 9L
gliosarcoma cells, the cells were irradiated with a 1.7 MeV
proton beam collimated to a 1 μm diameter and the emitted
gamma-rays were detected. The inter- and intracellular
distribution of 10 B in 9L gliosarcoma cells was directly
analyzed using micro-PIGE. The results showed that the
distribution of 10 B atoms was correctly measured. The
distribution of 10 B should have been evenly distributed in 9L
gliosarcoma cells and some 10 B atoms showed that
distribution. However, there was a significantly high
background and the detection of true 10 B atoms was not easy.
The main purpose of this study is to determine the optimum
conditions to apply this technique in an in vitro experiment.
Cultured 9L gliosarcoma cells were grown for 4 days on
a 5 μm thick polycarbonate film. These cells were treated
with 100 ppm, 250 ppm and 1,000 ppm of BSH,
respectively on the 3rd and 4th day. These cells were fixed
on the polycarbonate film with the acute freezing on the 5th
day.
The samples were analyzed to compare the distribution
image of the 10 B atoms using the micro-PIXE analysis
system at TIARA with a 30 to 60 minutes measuring time
and a measuring range from 25 × 25 μm to 100 × 100 μm,
respectively.
The peak 10 B atom measurement was small on the
measurement spectrum in comparison to the circumference
background. It was possible to confirm that 10 B atoms
were measured.
At the next step, a mask was created from the distribution
of sulphur and a suitable threshold value was determined.
Thereafter, a PIGE spectrum was created which was
specified by the masked portion and the whole spectrum was
compared to the masked spectrum.
It was possible to confirm the presence of a correlation in
the distribution of sulphur (S) or phosphorus (P) (tumor
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cells) and the distribution of 10 B atoms because the peak of
10
B atoms appeared more clearly in the masked spectrum.
A more clear correlation was observed between the
distribution of tumor cells and that of 10 B atoms distribution
when the two images were combined. This demonstrated
that the 10 B atom was accumulating around the tumor cells.
In this in vitro experiment, various conditions were
compared to determine the optimum conditions to yield
clear distribution images. The results showed that the
tumor- 10 B distribution was clearly demonstrated at a BSH
concentration of 250 ppm. The best measurement ranges
were from 50 × 50 μm to 100 × 100 μm and the optimum
measurement time to obtain the clearest image using PIGE
was from 30 to 60 minutes (Fig. 1).
P B
Fig. 1 Distribution of tumor cells (P) and 10 B(B).
Measurment time was 30 minutes.
However, the intracellular micro-distribution of boron
could not be clearly detected in this analysis.
Improvements are therefore necessary in the technical
methods of cell fixation, while the micro-PIXE analyzing
system also needs to be further upgraded.
References
1) J.A. Coderre et al., Radiat. Res. 149 (1998) 163-170.
2) M. Wegden et al., Nucl. Instrum. Meth. Phys. Res. B
219-220 (2004) 67-71.
3) K. Endo et al., Oncol. Res. 16 (2006) 57-65.