Dose dependence incidence of new pituitary deficits after Gamma Knife Surgery (GKS) of pituitary adenomas

Keywords: gamma knife, hormone dysfunction, pituitary adenoma, radiosurgery, outcome

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     Hormone status after radiosurgery is important to document.
     The aim is to define clinical and healthy-tissue dosimetric factors predicting the development of hypopituitarism after Gamma Knife treatments, in order to optimize the radiation delivery procedure.
     Between 2001 and 2008, 367 patients with a diagnosis of pituitary adenoma were treated in the Gamma Knife Centre of San Raffaele Hospital - Milan. Between 2001 and June 2007, they have been treated with Leksell gamma Knife Model C, after September 2007 with Gamma Knife Perfexion. In this study we decided to consider only 130 patients who had complete clinical information and a follow up of at least 6 months (6-103) after GK radiosurgery. Diagnosis was of non functioning pituitary adenoma (NFPA) in 68 patients and secreting pituitary adenoma (SPA) in 62.
      Hypopituitarism was defined as a new pituitary deficit in (at least) one of the three hormonal axes (hypogonadism, hypotiroidism and hypoadrenalism) that we considered in our analysis. Before GK radiosurgery, 62 patients had no prior pituitary deficit for all hormonal axes and 94 patients only for hypotiroidism and hypoadrenalism axes. Median marginal dose was 15 Gy (15-25 Gy) for NFPA and 25 Gy (12-25 Gy) for SPA at 50% reference isodose, in the same time treatment plans were optimized in order to use dose constrains utilized in our clinical practice. For all patients tumor, pituitary stalk and pituitary gland were outlined using the Elekta GammaPlan. The predictive value of the considered variables was tested by univariate and multivariate logistic analyses.
     After GK radiosurgery, more than 12% of the patients showed a new pituitary deficit in at least one of three hormonal axes taken into account. The Results of the univariate analyses showed that a few clinical and many dosimetric parameters were associated with a higher rate of new pituitary deficits. Preliminary Results of multivariate analysis, confirmed the significant correlation between the mean dose to the stalk and to the (healthy) pituitary and the rate of new pituitary toxicities.
     This was a retrospective study.
     The analysis showed a dose-dependence incidence of new hormonal deficits after GK.
     During planning definition, the risk of hypopituitarism could be reduced using the outlined dose-volume predictors.


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