الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Boron Neutron Capture Therapy (BNCT) is a promising method for treating the highly fatal brain tumor; glioblastoma multiform. It is a binary modality, in which use is made of two components simultaneously, viz. thermal neutrons and Boron-1 O.
However simple its principle is, the biophysics of BNCT is conversely very complicated. This is primarily due to the complexity of element composition of the brain. Furthermore; numerous components are contributing to the over all radiation dose both to normal brain and to tumor. Simple algebraic summation cannot be applied to these dose components, since each component should at first be weighed by its relative biological effectiveness (RBE) value. Unfortunately, there is no worldwide agreement on these RBE values. For this reason, the parameters required for accurate planning of BNCT of brain tumors located at different depths in brain remained obscure. The most important of these parameters is; the source neutron energy.
For a long time in the history of BNCT development; thermal source neutrons were employed, necessitating surgical incision of the brain to deliver the thermal neutrons directly to the tumor. However, this technique was, for obvious reasons, practically unacceptable. As a solution, higher than thermal neutrons (epithermal) were suggested as alternate to the thermal neutrons on the proposal that they would be thermalized while being transported in the brain tissues. However; debate was there regarding how ”high” should the source neutrons energy be; for treatment of brain tumors located at different depths in brain. Again, the insufficient knowledge regarding the RBE values of the different dose components was a major obstacle.
”Optimization”, the heading of the present study, is one of the three principles of radiological protection recommended by the ”International Commission on Radiological Protection (ICRP)”. It requires the employment of all radiation techniques, under optimum conditions. In other words, the radiation beam should be optimally tailored to the proposed application. Hence, the endeavor to seek the optimum source neutron energy for BNCT.
In the first part of the present study, a new concept in estimating the optimum source neutrons energy, for different circumstances of BNCT was applied. Four postulations on the optimum source neutrons energy were worked out, almost entirely independent of the RBE values of the different dose components. Four corresponding condition on the optimum source neutrons energy were deduced. An energy escalation study was carried out investigating 65 different source neutron energies, between 0.01 eVand 13.2 MeV. MCNP4B Monte_Carlo neutron transport code was utilized to study the behavior of neutrons in the brain. The deduced four conditions were applied to the results of the 65 steps of the neutron energy escalation study. A source neutron energy range of few electron volts (e V) to few tens of ke V s was estimated to be the most appropriate for BNCT of brain tumors located at different depths in brain.
In the second part of the present study, a real neutron source was selected and modeled.
The Californium-252 based subcritical multiplying assembly eS2Cf-SMA) proposed by Kim et al; (1998), was chosen. This was because its output neutron energy spectrum highly coincides with the energy range estimated in the first part of the present study.
The nuclear design of the chosen assembly was revised, using MCNP4B Monte_Carlo neutron transport code. The effective criticality factor Keff of the assembly was recalculated. The neutron spectrum at the beam-port was tallied. There was a good degree of agreement