MEGAVOLTAGE PITUITARY IRRADIATION LOWERS BUT SELDOM LEADS TO SAFE GH LEVELS IN ACROMEGALY - A LONG-TERM FOLLOW-UP-STUDY

Radiotherapy (RT) has long been used in the treatment of acromegaly, b ut confusion regarding the definition of biochemical cure has hampered interpretation of previous reports on the outcome of this treatment. In the present study we present additional data using the currently ac cepted criteria of biochemical cure in a large group of patients follo wed up by our department. Forty-six acromegalic patients were treated with external beam megavoltage RT and followed up for a mean of 7.6 ye ars (range 2-22 years). Only four patients had had previous surgical t reatment by either transsphenoidal or transfrontal routes. Following R T, mean basal GH levels decreased from 30.9 ng/ml (5-96 ng/ml) to 11.5 ng/ml (1-36 ng/ml) at 10 years of follow up with a further fall to 6. 1 ng/ml (1-29 ng/ml) in those patients followed up for more than 10 ye ars. As a result, although mean GH levels of less than 5 ng/ml were ac hieved in 9/28 (30.1%) at 5 years, 6/19 (31.6%) at 10 years, and in 6/ 11 (54.5%) of those patients followed up for more than 10 years post-R T, only 0/28 (0%), 7/28 (25%), 4/19 (21%) and 1/11 (1%) achieved GH le vels of 12.5 ng/ml at 2, 5, 10 and >10 years following RT. Thus, in th e whole series only 10/48 (20.8%) patients showed a decrease of GH lev el to less than 2.5 ng/ml at their latest follow up. Hypopituitarism a s a result of RT was only infrequently observed in this series; gonada l deficiency developed in 12 (26.6%) patients, thyrotrophin (TSH) defi ciency in 3 (6.6%) and adrenocorticotrophin deficiency in 2 (4.4%). In conclusion, megavoltage RT is an effective treatment for the control of GH hypersecretion in acromegaly, with a continuing lowering effect for several years following RT, but seldom leads to safe GH levels.