Protracted Long-Term Irradiation of Inoperable Midbrain Tumours by Stereotactic Curie-Therapy using Iridium-192

Abstract

While the semimalignant gliomas of the diencephalon, mesencephalon and cerebral trunk are inoperable by conventional neurosurgical methods, resistant to treatment with external techniques of irradiation^{2, 3, 4} and can be freed of internal pressure only through fluid-drainage operations, they have long been the targets of stereotactic operational treatment¹³ principally using the method of implanting radioactive gold-198 and yttrium-90 (Talairach and Szikla¹⁴, Hankinson¹, and others). We ourselves (Mundinger and Riechert) began using such implantations in 1954¹². Then starting in 1966 Mundinger undertook to implant iridium-192, with its half-live of 74 days, into most of the astroblastomas, oligoblastomas and spongioblastomas which we treated¹⁰. Prior to this we had gathered over 10 years of encouraging experience with iridium-192, using it for irradiation of semimalignant trabecular gliomas, gliomas of the hemisphere and pituitary adenomas^{6, 7, 8, 9}. Since this form of protracted long-term irradiation⁵ entails a relatively slow dosage accumulation over a period of 7 months, there is a gradual build-up of scar tissue and shrinkage of the tumour. Whereas the short-lived radioisotopes mentioned have a necrotic effect, the iridium-192 irradiation causes devitalisation and thus protects to a great extent the intact intermediate and surrounding neuronal structures and permits compensating processes to develop. This explains why, clinically as well, no reaction to irradiation is noted. The initially low sensitivity of these tumour cells towards radioactivity increases as a result of the long-term accumulation of irridiation doses, and thus they are more apt to be lethally affected by radioactivity than is the surrounding tissue. Moreover, continual emission of the doses ensures with great probability that the tumour cells in the periphery which have a premitotic pause will be lethally hit rather than the normal cells. This gives us an idea of the basically different radiobiologic mechanisms which are most advantageous for tumour localization. But it also makes it apparent that tumours showing malignant stigmata are unsuited for this type of long-term irradiation.

Supported by a Special Research Programme „Gehirnforschung und Sinnesphysiologie (SFB 70, IIId)“ of the Deutsche Forschungsgemeinschaft.