Neutron Capture Therapy with Gd-DTPA in Tumor-Bearing Rats
Gd-DTPA dimeglumine (Magnevist®) is widely used as contrast medium in magnetic resonance imaging (MRI). It is especially helpful for the delineation of brain tumors with an injured blood-brain barrier’. The dianion [Gd-DTPA]2− diffuses into the tumorous tissue and due to the large magnetic moment of the Gd3+-ion leads to a shortening of the water relaxation times’ and, consequently, to changes of the MRI signal intensities2. A number of pharmacologically well-tolerated Gd-complexes are clinically available or under clinical development. In addition to its diagnostic value, 157Gd with a natural abundance of 15.7% has the highest cross-section (255 000 barn (=10−24 cm2)) for thermal neutrons of all stable isotopes. Natural Gd has an average cross-section of 48 800 barn. After neutron capture the excited Gd-nuclei relax via the emission of photons with energies up to 7.9 MeV and a cascade of conversion and Auger electrons. Therefore, Gd-complexes have been suggested as agents for neutron capture therapy (NCT)3–6 and NCT effects of Gd-complexes have been studied in phantoms’, on the DNA level’, and in both in vitro and in vivo systems9–13 A therapeutic gain has been demonstrated experimentally for extracellular Gd-complexes9–13 although the discussion on the contributions of prompt γ’s or electrons to the therapeutic effect is not yet settled. In the following we report on experiments performed with a rat tumor model and administration of Gd-DTPA prior to irradiation with epithermal neutrons.
KeywordsEpithermal Neutron Post Irradiation Capture Reaction Therapeutic Gain Large Magnetic Moment
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