The authors analyzed long-term follow-up data to assess the value of intracavitary irradiation with stereotactically implanted beta-emitting
radioisotope (90)Y-silicate
colloid for the treatment of
craniopharyngiomas. Fifty-seven
craniopharyngiomas in 42 patients were selected for retrospective analysis. The
yttrium-90 was implanted intracavitally, using computerized tomography-guided and three-dimensional stereotactic treatment planning. The cumulative dose aimed at the inner surface of the
cyst wall was 300 Gy. An average of 75% shrinkage of the initial
cyst volume was observed. In 18 cases the reduction was more than 91%, and the
cyst disappeared totally in 11 cases. A 50% decrease in
cyst volume was usually apparent between the 2nd and 4th months. A 70% decrease in
cyst volume was seen by the 5th and 6th months and an 80% reduction by the 7th and 8th months.
Cysts that were unchanged remained so throughout the observation period. The time course of volume reduction could be expressed mathematically by the formula of 0.73 X e(-0.62 X T) + 0.27, where "e" is the basic number of natural logarithm and "T" is the time expressed in months. Mean survival duration after intracavitary irradiation was 9.4 years. The shrinkage of the
cyst was a consequence of
fibrosis of the wall, as seen on histopathological examination. The neuroophthalmological prognosis was favorable only when the optic disc was normal or nearly normal at the time of the treatment. In the presence of preexisting
optic atrophy, visual deterioration proved to be irreversible. The long-term results support the view that intracavitary (90)Y-irradiation is a noninvasive and very effective method of treatment for
craniopharyngioma cysts. Because of the 1.1 mm half-life decay of beta irradiation, it cannot influence the solid part of the
tumor; therefore, the best result can be expected in
solitary cysts.