Introduction: Radiotherapy is an important adjuvant treatment for pituitary and cranial diseases. The aim of the study was to observe response of Radiotherapy (RTX) on HypothalamicPituitaryAdrenal (HPA) axis determined by serial Short Synacthen tests (SSTs).
Methods: Patients treated with adjuvant Cranial Radiotherapy between the years 2000 and 2018 in the department of Radiation Oncology and who also underwent serial Short Synacthen tests, in the department of Endocrinology, in a tertiary care centre, were reviewed retrospectively. Patient details were initially obtained from local dynamic test database, maintained by Endocrine Nurse Specialist. Details of total radiation doses in Grays (Gy) were provided by Radiation Oncology department. The patients underwent serial SSTs to assess HPA axis before and after radiotherapy. Assay specific cut-offs were measured for cortisol responses at 30 and 60 min to interpret results as either pass or fail. Cortisol levels at 30 min or 60 min or both below cut-offs resulted in diagnosis of secondary Adrenal Insufficiency (AI) leading to initiation of corticosteroid replacement therapy.
Results: In total, 32 patients received adjuvant radiotherapy (mean dose 44.5 Grays, median 3560 Grays) between the years 2000 and 2018. These doses were delivered in 25 to 40 fractions over 29 to 40 days. Twenty patients underwent Pituitary surgical interventions. A total of 169 SSTs were performed before and after radiotherapy. Intact HPA axis was observed in 21/32 (65%) patients, while in 11/32 (34%) patients there was sub-optimal response after mean duration of 7.6 years (median 120 years) consistent with secondary AI.
Conclusion: The findings of the study showed HPA axis failure in one third of the patients who received cranial radiotherapy for pituitary or cranial diseases. Further large scale studies are needed to validate our findings.