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Title:
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Design of a [gamma]-ray analysis system for determination of boron in a patient's head, during neutron irradiation
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Author(s):
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Published by:
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Publication date:
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ECN
NUCLEAIR
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1997
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ECN report number:
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Document type:
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ECN-I--97-057
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Other
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Number of pages:
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Full text:
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69
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Download PDF
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Abstract:
Boron Neutron Capture Therapy (BNCT) is a new radiation therapy in whichthermal neutron capture by "1"0B is used for the selective destruction of a
cancer tumour. At the High Flux Reactor (HFR) in Petten, Netherlands, a
therapy facility is built for the neutron irradiations. In first instance,
patients with a brain tumour will be treated. The doses delivered to the
tumour and to the healthy tissue depend on the thermal neutron fluence and on
the boron concentrations in these regions. Yet, both concentrations change in
time after the administration of the tumour-seeking boron compound. An
accurate determination of the patient's dose requires the knowledge of these
time dependent concentrations during the therapy. For this reason, a
gamma-ray telescope system, together with a reconstruction tool, are
developed. Two HPGe-detectors measure the 478 keV prompt gamma-rays which
are emitted at the boron neutron capture reaction, in a large background of
gamma-rays and neutrons. By using the detectors in a telescope
configuration, only gamma-rays emitted by a small specific region are
detected. The best shielding of the detectors is obtained by performing the
measurements through a small hole in the iron roof. A reconstruction tool is
developed to calculate absolute boron concentrations using the measured boron
gamma-ray detection rates. Besides the boron gamma-rays, a large
component of 2.2 MeV gamma-rays emitted at thermal neutron capture in
hydrogen is measured. Since the hydrogen distribution is almost homogeneous
over the head, this component can serve as a measure of the total number of
thermal neutrons in the observed volume. By using the hydrogen gamma-line
for normalisation of the boron concentration, the reconstruction tool
eliminates the greater part of the influence of the inhomogeneity of the
thermal neutron distribution. MCNP calculations are used as a tool for the
optimisation of the detector configuration. Experiments on a head phantom
with 5 ppm 10B in healthy tissue and 62 ppm in the tumour proved that the
minimum measuring time is 2 minutes live time. The reconstruction provided
deviations of the boron concentrations of 5% for the healthy tissue and 15%
for the tumour. 13 figs., 1 tab., 10 refs., 10 appendices
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