Endocrine Abstracts

Radiation therapy is used in the treatment of pituitary adenomas, especially in failures of neurosurgery and pharmacotherapy to reduce the size of adenomas and normalize their hypersecretion. Conventional fractionated radiotherapy has achieved good results, but only after a long latency, with considerable postradiation morbidity and with very frequent appearance of hypopituitarism. The focal stereotactic targeting allowed by Leksell gamma-knife (LGK) was supposed to decrease the incidence of hypopituitarism, however our first patients treated by LGK developed hypopituitarism in 38.2%. Consequently, we have analyzed factors leading to this unfavorable outcome and suggested that the mean dose of irradiation on pituitary tissue is the most important cause of hypopituitarism.

Results: Seventy-five patients (47 women and 28 men) with pituitary adenomas (39 with acromegaly, 17 prolactinomas, 8 with Cushing’s disease, 1 with Nelson’s syndrome and 9 functionless adenomas), where the mean dose of irradiation on pituitary tissue was measured, were followed 60–180 (mean 91.1) months. In 41 patients, the mean dose of irradiation on pituitary was more than 15 Gy. The hypopituitarism at least in one axis developed in 29 (70.7%) patients during 10–126 months after the irradiation. In 34 patients, the mean dose on pituitary was less than 15 Gy. Only one patient (1.2%) developed hypopituitarism 12 months after the irradiation. This patient had undergone two previous pituitary surgeries and had already central hypothyreosis when irradiated.

Conclusion: To avoid hypopituitarism the radiation dose of 15 Gy is the maximum safe limit of the mean dose of radiation to the pituitary tissue surrounding the adenoma. This cut off should become a rule when irradiating pituitary adenomas – just like the dose rules of 7 Gy on the optical tract or 14 Gy on the brainstem.