Timing Of Radiotherapy

There is considerable debate about the appropriate timing of radiotherapy in patients with residual nonfunctioning adenoma after surgery. Although postoperative radiotherapy is effective with a low risk of subsequent recurrence, the indolent natural history of pituitary adenoma means that a proportion of patients remain with a static tumor for long periods and some may avoid the need for irradiation. However, a policy of observation requires close surveillance with regular imaging and ophthalmologic assessments and, occasionally, a need for a second surgical intervention with consequent morbidity. Currently, there are no hard data to define the most appropriate timing of radiotherapy (immediate vs delayed), and a randomized study comparing the two policies is required. Such a study should particularly concentrate on the endpoints of long-term effects of the tumor and therapy in terms of functional outcome and survival.

In the absence of data that can identify the preferred policy, there are several factors to consider when deciding on the appropriate timing of radiotherapy. Age and performance status give an indication of tolerance and morbidity of further surgery, and age is an important consideration in the likelihood and the potential duration of hypopituitarism. Older patients and those with poor performance status could therefore be offered radiation earlier rather than later. Established pituitary dysfunction avoids the concern of radiation-induced hypopituitarism and in this situation, radiotherapy can also be given earlier. Tumor size and its proximity to the optic apparatus would favor earlier treatment to reduce the risk of optic chiasm compression and a further potential need for decompressive surgery. Conversely, a small amount of residual tumor after radical surgery or patients with initially small adenomas do not require immediate postsurgical treatment with irradiation.

An important factor, which helps to decide on the timing of radiotherapy, is the biologic behavior of the residual tumor. Although some information can be obtained from proliferation indices (60) and apparent tumor invasiveness, the rate of tumor growth can currently only be assessed with some certainty by interval imaging. The rate of change in the size of the residual tumor indicates how urgently irradiation should be started.

Patients with excess hormone secretion after primary therapy are considered for early radiotherapy to shorten the duration of elevated hormone levels.

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