Radiation Effects of Iridium-192 Implants in the Cat Brain

Die Folgen lokaler Bestrahlung durch permanent in das Katzengehirn implantiertes ¹⁹²Ir wurden hinsichtlich morphologischer Veränderungen, zerebraler Durchblutung, Wasser- und Elektrolytgehalt untersucht. Radioaktive ¹⁹²Ir-Draht-stückchen wurden bei 10 Tieren sowie inaktive Silberdrähte bei 5 Kontrolltieren stereotaktisch in die linke innere Kapsel implantiert. Die Aktivität des ¹⁹²Ir betrug 0,31 mCi, die akkumulierte Dosis in 5 mm Abstand nach 21 Tagen 3060 rad und nach 35 Tagen 4680 rad. Neurologische Ausfälle oder wesentliche EEG-Veränderungen waren nicht zu beobachten. Auch Gewebsnekrosen fehlten. Dagegen fand sich immunhistochemisch eine Einlagerung von Serumproteinen in reaktiven Astrozyten (3 x), in Makrophagen (2 x) und als diffuse perivaskuläre Einlagerung. Der Wassergehalt der weißen Substanz zeigte einen Anstieg von 68,6 auf 73,2%, was mit einem Volumenanstieg von 17% einherging. Die zerebrale Durchblutung war insgesamt verringert. Die Veränderungen lassen annehmen, daß durch die lokale interstitielle Bestrahlung mit niedrigen Dosisraten in erster Linie Schädigungen an der Gefäßmembran hervorgerufen werden, die ein lokales Ödem zur Folge haben.

The radiation effects of ¹⁹²Ir permanent implants into the cat brain were studied with respect to morphological changes, blood flow, brain water and electrolytes. ¹⁹²Ir wires (10 animals) and non-radioactive silver wires (5 control animals) were placed stereotactically into the left internal capsule. Activity of ¹⁹²Ir was 0.31 mCi, the accumulated dose at 5 mm distance was 3060 rad after 21 days and 4680 rad after 35 days, respectively. None of the animals presented a neurological deficit, and the EEG recording was without significant changes. Histological damage which could be attributed to the radiation was not observed. Serum proteins, however, were detected immunohistochemically in reactive astrocytes (3 x), in macrophages (2 x) and as diffuse perivascular accumulation. Brain water in the white matter near the implantation site increased from 68.6 to 73.2%, corresponding to a volume increase of about 17%. There was no change in the grey matter or the opposite hemisphere. Cerebral blood flow decreased slightly but there was no relationship with the development of edema. The findings suggest that low dose rate topical irradiation of the brain produces primarily membrane-dependent changes, resulting in local brain edema.

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