Introduction: Radiotherapy (RT) can achieve tumour control rates of over 90% in patients with pituitary adenomas. The commonest toxicity of irradiation is hypopituitarism. The exact incidence is variable and requires long-term intermittent testing for deficiency of all hypothalamic−pituitary axes (HPA). The aim of this study is to determine the time to onset of individual hormonal deficiencies and establish a time frame for endocrine testing during follow-up post-RT.
Methods: We retrospectively assessed the late effects of irradiation on pituitary function in patients with pituitary adenomas treated over 2004−2015. Patients with acromegaly or Cushings disease, those with tumour recurrence undergoing surgery after radiotherapy and patients with incomplete endocrine data during follow-up were excluded.
Results: 94 patients (59% male; age at RT 58.4±12.3 years) were included. Mean duration of endocrine follow-up post-RT was 7.6±3.1 (range: 1.3−14.3) years. 90.4% of patients (n=85) received external beam radiotherapy. Thirty patients (31.9%) had complete loss of anterior pituitary hormone function pre-RT. Overall prevalence of radiation-induced hypopituitarism was 65.6%. The incidence and mean time to onset of individual hormone deficits post-RT were: GH57.1% (8/14, 1.3±0.7 years); LH/FSH50% (11/22, 2.0±1.4 years); ACTH43.3% (26/60, 3.1±2.2 years, P=0.04); TSH39.6% (19/48, 2.9±1.7 years, P=0.01). Age at RT, gender, dose of RT and severity of hypopituitarism pre-RT did not correlate with post-RT hypopituitarism. By 5 years 100% GH, 75% LH/FSH, 60% ACTH and 75% TSH deficiencies were evident. All HPA dysfunction were detected by 8 years.
Conclusion: A gradual increase in the prevalence of all anterior pituitary hormone deficits was observed. GH axis was the most radiosensitive and ACTH deficiency was of slowest onset. Regular testing is mandatory for at least 8 years to ensure timely diagnosis and early hormone replacement therapy.