Role of Radiation Therapy in Clinical Hormonally Active Pituitary Adenomas: An Update of Their Efficacy and Safety

Introduction: Radiation therapy (RT) plays an important role in treatment of pituitary tumors that are resistant to medical and surgical therapy. The continuous development in the field of RT warrants a reassessment of its role as either initial or adjuvant therapy in the treatment of pituitary tumors and the adverse effects of this treatment.

Objective: The purpose of this study is to assess the outcome of RT as observed in the treatment of hormonally active and inactive pituitary adenomas. An emphasis is placed on identifying potential prognostic factors, determining the control rate after radiation and evaluating late toxicity.

Methodology: From 1997 to 2010, 125 patients with pituitary adenomas received RT, 35 of which were hormonally active pituitary adenomas. The median age was 52 years (range, 28–79 years), with 21 females and 14 males for the hormonally active patients. There were 18 patients with growth hormone secreting, 5 prolactinoma, and 12 with Cushing's disease. The median follow-up was 2.2 years. Tumor control was defined as normalization of basal hormone level and lack of progression of adenoma assessed by imaging studies. The variables assessed for tumor control were: age, sex, tumor type, tumor extension, radiation dose, and radiation field size.

Results: Radiotherapy resulted in stable outcome in 95% of patients with inactive pituitary adenomas. Stable outcome was seen in 74% of hormonally active patients with 24% not requiring any further drug therapy. Hypopitutiarism in one or more axis was observed in 52% of the cases, with inactive pituitary adenomas and 29% of the cases with hormonally active disease. One patient died due to development of pituitary carcinoma. Cause-specific survival rate was 97% during the course of the study. None of the prognostic factors for tumor control were found to be significant. On univariate and multivariate analyses, none of the factors investigated were identified as predictors of response to RT.

Conclusions: Postoperative RT is indeed effective in gaining tumor control and thus nullifying the space-occupying effects of hormonally active pituitary adenomas. However, RT falls short in the sphere of biochemical control, which was observed in less than half of the cohort in our study. In terms of acute and late effects of RT, data from our study support the previously well documented adverse effects, with new-onset hypopituitarism as the most frequent complication. No patient experienced radiation optic neuropathy or CNS malignancy in the field of radiation. No predictors of adverse radiation effects were identified.