Abstract
The main detectors for characterising and controlling of
BNCT beams are activation foils and paired ionisation
chambers. Thermoluminescent (TL) dosimeters are also of
interest because of their following advanta: i) small
physical size, ii) need for high voltage or cables, i.e.
stand alone character, and iii) suitability for large
scale measurements; with TL dosimeters it is possible to
measure depth dose curves and profiles at the same time,
with one irradiation. Also, TL dosimeters may be possible
detectors for in vivo use. At the Finnish BNCT facility,
a TL detector MTS-Ns of TLD Niewiadomski & Co. (Krakow,
Poland) with an ultra-thin active Lif:Mg,Ti layer for
small self-shielding of thermal neutrons was selected for
use as a neutron sensitive dosimeter. A TL detector
MCP-7s (7Lif:Mg,Cu,P) of the same manufacturer was used
for gamma detection because of its high sensitivity to
gamma radiation compared to that to high LET radiation.
The gamma dose and neutron fluence distributions have
been measured in PMMA, water and brain substitute liquid
phantoms at the BNCT beam. Gamma dose and neutron fluence
profiles measured with TL detectors correlate with those
calculated using DORT (Two Dimensional Discrete Ordinates
Transport Code) and measured with ionisation chambers.
MTS-Ns TL detectors were found to measure accurately (8
%, 1 S.D.) the relative neutron fluence, and therfore to
be a useful addition to the activation foils in bnct
neutron dosimetry. Due to the high uncertainty of the
thermal neutron sensitivity of the MCP-7s TL detectors,
the absorbed gamma doses can be measured with MCP-7s
detectors within 20% in the mixed neutron-gamma field of
BNCT. The treatments of glioma patients at the Finnish
BNCT facility will start in the spring 1999. The doses to
the target volume and sensitive organs, i.e. brain, will
be calculated individually in the dose planning. Since it
is also necessary to monitor the absorbed doses to the
head and to the body, in vivo dosimeters are used. For
clinical practice, when verifying the absorbed doses in
vivo the used TL and activation foil dosimeters must be
placed on the skin of the patient of in accessible
cavities. The TL detector MCP-7s will be used in in vivo
gamma dosimetry. The correlations for the thermal neutron
sensitivity of the MCP-7s TL detectors will be made based
on the neutron fluence measured with activation foils.
The accuracy of approximately 10% can be achieved in
those measurement points, in which thermal neutron
fluence is negligible and, therefore, no correlation for
thermal neutron sensitivity is required. This applies to
those measurement points in the body, i.e. total body
dose.
Original language | English |
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Title of host publication | Current status of neutron capture therapy |
Place of Publication | Vienna |
Publisher | International Atomic Energy Agency IAEA |
Chapter | Annex 5 |
Pages | 165-174 |
Publication status | Published - 2001 |
MoE publication type | D2 Article in professional manuals or guides or professional information systems or text book material |