Telecobalt irradiation in combination with intrathecal (IT) methotrexate has been replaced by IT 198Au-colloid and methotrexate for meningosis prophylaxis in leukemia. Seventy-seven children received 56-200 MBq 198Au-colloid. The distribution was measured with a scintillation camera having a data processing facility. The radiopharmaceutical is adsorbed at the surface of the spaces with cerebrospinal fluid (CSF) 10-20 h after application. The normal retention of the administered radioactivity in the intracranial subarachnoid space (ISS) and in the spinal subarachnoid space (SSS) were 52 +/- 10% and 26 +/- 9%, respectively. An impairment of the normal distribution was observed after IT methotrexate and also postinjection CSF leakage. The calculated radiation absorbed doses in the cerebral and spinal meninges at a depth of 0.01 cm, i.e. the thickness of the pia, were 45 +/- 17 mGy and 189 +/- 91 mGy, respectively, for 1 MBq administered 198Au-colloid. The dosimetry shows that an effective radiation absorbed dose of 18 Gy can be delivered to the cerebral meninges by the application of 400 MBq 198Au-colloid.

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