Internal irradiation for cystic craniopharyngioma

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Abstract
The results of internal irradiation with labeled chromic phosphate (32P) and gold-198 (198 Au) colloid in 8 cases of cystic craniopharyngiomas are reported. A newly developed dosimetric formula was used by which the radiation dose at the cyst wall and at any point far from the radioactive source can be calculated. Ten courses of irradiation in 8 patients were carried out by injection of 32P or 198Au colloid into the cyst through an Ommaya drainage system that had been placed at craniotomy. Follow-up studies ranging from 13-156 mo. revealed that all cysts were effectively treated, with elimination of fluid or collapse of the cyst. This was confirmed by Conray cystography and/or computerized tomography. Not only the dose delivered to the wall but also the thickness of the cyst wall and the location of the cyst are important factors in planning internal irradiation. A safe and adequate dose to the cyst wall could range between 9000-30,000 rad for craniopharyngioma. This treatment is suitable for large cysts that are thought to be difficult to remove radically, recurrent cysts resistant to previous treatment or multiple cysts. Internal irradiation may also be applicable in other cystic intracranial tumors if dosimetry is calculated accurately.