Radiation therapy in the multimodal treatment approach of pituitary adenoma

Pituitary tumors are relatively uncommon, comprising 10-12% of all intracranial tumors. The treatment consisting of surgery, radiotherapy and drug therapy or a combination of these modalities is aimed at the control of tumor cell proliferation and--in endocrine active tumors--the reduction of hormone secretion. However, the slow proliferation characteristics of pituitary tumors necessitate long-term studies for the evaluation of the treatment results. In the last decade there has been continuous improvement in surgical procedures, radiotherapy techniques and drug generation. In this paper, literature will be reviewed to assess the role of modern radiotherapy and radiosurgery in the management of pituitary adenomas.

Nowadays, magnetic resonance imaging for the definition of the target volume and a real three-dimensional (3-D) treatment planning with field conformation and the possibility for non-coplanar irradiation has to be recommended. Most groups irradiate these benign tumors with single doses of 1.8-2.0 Gy up to a total dose of 45 Gy or 50.4 Gy in extensive parasellar adenomas. Adenomas are mostly small, well circumscribed lesions, and have, therefore, attracted the use of stereotactically guided high-precision irradiation techniques which allow extreme focussing and provide steep dose gradients with selective treatment of the target and optimal protection of the surrounding brain tissue.

Radiation therapy controls tumor growth in 80-98% of patients with non-secreting adenomas and 67-89% for endocrine active tumors. Reviewing the recent literature including endocrine active and non-secreting adenomas, irradiated postoperatively or in case of recurrence the 5-, 10- and 15-year local control rates amount 92%, 89% and 79%. In cases of microprolactinoma primary therapy consists of dopamine agonists. Irradiation should be preferred in patients with macroprolactinomas, when drug therapy and/or surgery failed or for patients medically unsuitable for surgery. Reduction and control of prolactin secretion can be achieved in 44-70% of patients. After radiotherapy in acromegaly patients somatomedin-C and growth hormone concentrations decrease to normal levels in 70-90%, with a decrease rate of 10-30% per year. Hypercortisolism is controlled in 50-83% of adults and 80% of children with Cushing's disease, generally in less than 9 months. Hypopituitarism is the most common side effect of pituitary irradiation with an incidence of 13-56%. Long-term overall risk for brain necrosis in a total of 1,388 analyzed patients was estimated to be 0.2%. Other side effects are rare too, and do also depend on the damage produced by tumor itself or preceding surgery. They include deterioration of vision in 1.7% of all cases, vascular changes in 6.3%, neuropsychological disorders such as dementia in 0.7% and secondary malignancies in 0.8%, if single doses of 2.0 Gy and total doses of 50 Gy are not exceeded.

Conventional radiation therapy of pituitary adenoma is highly effective. It is recommended after subtotal resection of primary tumors such as macroadenomas, after gross total resection from endocrine active adenomas with postsurgical hormone secretion and for recurrent tumors. Radiosurgery seems to be a possible treatment alternative in experienced centers, and only in patients with adenomas smaller than 25-30 mm with a minimum distance of 2-3 mm to the chiasm.