Download boron concentration (ppm)

A Study of Effective Dose for Tumor in BNCT
Y. Sakurai, H. Tanaka, N. Fujimoto, N. Kondo, M. Narabayashi, Y. Nakagawa, T. Watanabe,
Y. Kinashi, M. Suzuki, S. Masunaga, A. Maruhashi and K. Ono
Kyoto University Research Reactor Institute, Osaka, Japan
INTRODUCTION
 In BNCT at Heavy Water Neutron Irradiation Facility of Kyoto
University Reactor (KUR-HWNIF), boron dose is estimated
based on the following equation:
RESULTS & DISCUSSIONS
 In BNCT performed at KUR from 2012 to 2013, 39 irradiations were for
head and neck tumors with BPA only, 41 irradiations for brain tumors
with BPA only, and 14 irradiations for brain tumors with BPA and BSH.
Boron dose = CBPA × RT/B × CBEBPA × DBPA
+ CBSH × CBEBSH × DBSH
C: boron concentration (ppm),
RT/B: ratio of tumor to blood (T/B ratio) for BPA,
CBE: compound biological effectiveness,
D: physical dose per 1ppm of boron-10 (Gy/ppm).
 The used boron concentration is for whole blood. The degree of
BPA uptake for tumorous cell is expressed using T/B ratio based
on whole blood.
 In clinical study, T/B ratio is decided using the result by F-BPAPET. However, BPA uptake is smaller than T/B ratio, or almost
zero in some actual tumorous cells.
 We are reconsidering the definition of effective dose for tumors in
BNCT.
BPA(80 points)
P/B=1.28±0.08
BSH(14 points)
P/B=1.44±0.09
Figure 3 P/B ratios for the clinical studies at KUR.
 The minimum-estimated dose and sub-maximum-estimated dose were reestimated for the three respective BNCT irradiations in three groups such
as H&N tumors, brain tumors with BPA only, and with BPA and BSH.
Whole: 26.0ppm, and T/B=3.0.
Plasma: 32.0ppm. P/B=1.23.
Min.-estimation is 32-34% for
Sub-Max. estimation.
MATERIALS & METHODS
 Tumor dose was re-estimated for the recent BNCT clinical
studies, performed at KUR-FWNIF.
 For the boron dose for tumor due to BPA, it was assumed that the
conventional dose based on T/B ratio was considered to be the
sub-maximum-estimated dose, and CBE was assumed to be 3.8.
 For the minimum-estimated value, boron dose was considered to
be similar to that for BSH, as BPA exists just surround the cell.
CBE was assumed to be 2.5, the same for BSH.
Figure 4 Result for Brain only with BPA.
Table 1 Summary of the calculated results for tumor dose
CONCLUSION
Figure 1 Boron distribution for submaximum-estimated dose. T/B ratio is
decided by F-BPA-PET. CBE = 3.8.
Figure 2 Boron distribution for minimumestimated dose. BPA exists just surround
the cell. CBE = 2.5 ?
 At present, dose estimation is performed using boron
concentration of whole blood, both for BPA and BSH. The used
CBEs and T/B ratio are decided also based on boron
concentration of whole blood.
 In actual, the surrounding of cell is filled with not blood but
interstitial fluid. It can be assumed that the concentration in
interstitial fluid equals the concentration in plasma.
 Accordingly, boron dose for tumor was assumed to be as follows.
The boron concentration for whole blood was used in maximum
estimation. In minimum estimation, the boron concentration for
plasma was used.
 Based on the re-estimation for tumor dose, the target dose should be
decided in consideration of Min.-estimated dose, for the larger T/B ratio.
 In actual, the cells with larger BPA-uptake and smaller BPA-uptake are
mixed. There is thought to be an “effective dose”, between Min. and SubMax.-estimated doses.
Curve for
effective dose
 Comparison of the clinical effects for the similar Sub-Max doses is needed.
 For the smaller-effect case, it is suspected that many cells didn’t uptake
BPA. So, the effective dose is close to Min.-estimated dose.
 For the larger-effect case, the effective dose is close to Sub-Max estimation.