Comparison Of Gamma Knife Radiosurgery With Conventional Radiation

Precise comparison of many of the studies of conventional pituitary radiation and Gamma Knife radiosurgery is not truly possible because of limited information and because some of the conventional radiation studies are older and do not use modern criteria for cure or remission. Despite these limitations, some assessment is warranted. The most widely referenced study of conventional radiation for acromegaly is that of Eastman and colleagues. This study was published in 1979 and considered "remission" as a serum GH of <5 ^g/L (10 mU/L) It is now known that this does not reflect remission or cure. In this study of 47 patients, 69% achieved a serum GH of <5 ^g/L within 10 yr of treatment (8). Another study of conventional radiation in 46 patients with acromegaly found that 26% of patients achieved a mean serum GH of <2.5 ^g/L (5 mU/L) (an acceptable criterion for remission), seven within 5 yr, four within 10 yr, and one more than 10 yr after treatment (9). A more recent study by Barkan and colleagues reported the effects of conventional radiation in 38 patients with acromegaly. Achievement of a normal serum IGF-1 occurred in two patients followed for an average of 6.8 yr (10). In patients with CD, a study of 30 patients found that 25 patients (83%) treated with conventional radiation achieved remission at a median of 42 mo (range 18-114 mo) after treatment (11). In 26 patients with a PRL-secreting adenoma treated with conventional radiation, 3 achieved a normal serum PRL within 4 yr of treatment (12).

As noted, development of new pituitary hormone deficiency should be anticipated and treated promptly. Additional reported complications of Gamma Knife radiosurgery include development of a radiation-induced neoplasm. Two patients developed a glioblastoma multiforme 7.5 and 20 yr, respectively, after Gamma Knife treatment. One patient was treated for a vestibular schwannoma and the other for a cerebral arteriovenous malformation (13,14). As in one patient in our series, damage to vision may occur, requiring regular ophthalmologic evalution.

Although it is difficult to compare precisely the results of conventional radiotherapy with Gamma Knife radiosurgery because of differences in criteria for remission, Gamma Knife radiosurgery is effective earlier than conventional radiotherapy in reducing excessive hormone secretion to normal. It is also evident that both conventional radiation and Gamma Knife treatment cause new pituitary hormone deficiencies requiring regular monitoring and hormone replacement as indicated.

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