Repeat megavoltage irradiation of pituitary and suprasellar tumors

From 1965 to 1984, ten patients with suprasellar or pituitary tumors received repeat courses of radiation therapy at the Joint Radiation Oncology Center of the University of Pittsburgh. The radiation doses varied between 36.00 to 53.65 Gy for the first treatment course and from 35.00 to 49.60 Gy for retreatment. Six patients were treated for pituitary tumors, two for germinoma, one for optic glioma, and one for craniopharyngioma. One died of disease progression 19 years after a second course of radiation. Two patients were dead of intercurrent disease 0.2 and 1.5 years after repeat radiation. The remainder are free of disease progression 1.6 to 20.5 years after repeat irradiation. Optic neuropathy developed in one patient 1.3 years following a second course of treatment to 40 Gy in 20 fractions administered 7.5 years after initial treatment to 46 Gy in 23 fractions. Neither the Nominal Standard Dose nor the Neuret formula provided an adequate estimate of the repair of radiation. An estimation that 40% of the original radiation dose effect is still present appears to be a reasonable "rule of thumb" guideline to account for prior radiotherapy.