Radiation Therapy

Pituitary tumors are rarely treated primarily with external beam radiotherapy, because radiation takes many years to work, is not extremely effective in controlling size, and usually leads to pituitary hormone deficiencies. However, in some cases, primary radiation therapy may be considered for these tumors. More commonly, radiation therapy is used as an adjuvant treatment after surgery to prevent tumor regrowth (16). Conventional radiation therapy is administered to the tumor area via a linear accelerator through multiple ports to deliver 45 Gy throughout 5-6 wk (see Chapter 13). With this technique, there is a slow and variable tumor response in terms of stabilization or decrease in tumor size. Published reports indicate a 3% to 26% tumor recurrence rate with postoperative radiotherapy (16). However, these studies include heterogenous patient groups, radiation doses, and tumor characteristics, and it is difficult to extrapolate these results to individual patients. There is also a high incidence of the eventual development of hypopituitarism, anecdotal evidence of adverse neuropsycho-logic effects, and case reports of second brain tumors or other central nervous system complications after conventional radiotherapy (16,17).

More recently, stereotactic radiosurgery has been used in pituitary tumors to circumvent some of these problems (18-20). This uses a high dose of ionizing radiation delivered in a precisely defined, tightly concentrated field with a steep fall-off and little radiation to surrounding tissue. Details of this technique are described in Chapter 14. To date, there are limited data regarding efficacy and side effects of stereotactic radiosurgery applied to nonfunctioning pituitary adenomas. The procedure is effective in stabilizing tumor size in most patients, with frequent reports of actual tumor shrinkage. Rates of development of hypopituitarism were initially stated to be low, but further follow-up of treated patients has revealed increasing rates of hypopituitarism with time. It should be noted that hypopituitarism occurs more quickly with stereotactic radiosurgery compared with conventional radiotherapy, and these patients must be followed closely for this side effect.

Because many nonfunctioning pituitary tumors are large and cannot be completely removed by surgery, the question of postoperative radiation therapy often arises. In many cases, the tumor has been sufficiently debulked and can be monitored without further treatment, even with known residual tumor present. In these cases, MRI scans can be recommended to be performed 6 mo after surgery and then repeated on an annual basis or according to similar protocols. If the tumor shows signs of regrowth, repeat surgery or radiation therapy can be considered. This decision is based on patient characteristics, as well as the size, location, and expected aggressiveness of the residual tumor.

Was this article helpful?

0 0

Post a comment