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Long term effect of external pituitary irradiation on IGF1 levels in patients with acromegaly free of adjunctive treatment

¹ Regional Centre for Endocrinology and Diabetes² Regional Endocrine Laboratory, Royal Victoria Hospital, Belfast BT12 6BA, UK³ Northern Ireland Cancer Centre, Belfast City Hospital, Belfast BT9 7AB, UK

(Correspondence should be addressed to A B Atkinson; Email: brew.atkinson{at}belfasttrust.hscni.net)

Objective: It is established that external pituitary irradiation (EPI) effectively reduces serum GH levels in acromegaly. However, its effect in normalising serum IGF1 has been disputed. We looked at the number of our patients who achieved persistently normal IGF1 levels whilst free of adjunctive treatment for at least 1 year after EPI.

Patients and design: We identified 63 acromegalic patients between 1964 and 2004 who received EPI. Six were excluded: three had surgery after EPI, two had no medical records available, and one had a pituitary Yttrium implant.

Measurements: Patients received 4500–5000 cGy in fractionated doses. IGF1 levels were correlated with their respective age-related reference ranges.

Results: After EPI, the number of patients with normal IGF1 and free of adjunctive medical treatment for at least 1 year were four patients by 3 years, nine patients by 5 years and seventeen by 10 years, with the current number of 25/57 (44%). Concordance between IGF1 levels and random GH dropped from 90% at the time of EPI to 65% at 3 years, 66% at 5 years and 71% at 10 years.

Conclusions: We have demonstrated that, with time, EPI achieves a normal IGF1 in significant numbers of patients with acromegaly, thus obviating the need for life-long expensive medical therapy. For each patient this benefit has to be weighed against the possibility of new hypopituitarism as a result of the treatment. Any decision to use EPI is easier in the context of pre-existent hypopituitarism.