Potentially radiation-induced late toxicity after irradiation of pituitary adenoma, a retrospective dosimetric study

BACKGROUND: Radiotherapy is considered as a second or third-line treatment for recurrent pituitary adenomas. As it is a benign tumor, the balance should clearly favor the benefit and induce the least amount of side effects. PURPOSE: This retrospective study aims to evaluate the incidence of side effects after treatment and their actual causality with radiotherapy through dosimetric analysis. METHODS: A cohort of 35 patients who underwent normofractionated radiation therapy following unsuccessful surgical or medical interventions was identified. 48.6% (17/35) had functioning adenomas (29.41% adrenocorticotrophic hormone-secreting, 35.3% growth hormone-secreting, and 23.5% prolactin-secreting adenomas). Surgery was previously employed in 94.29% of patients. A median dose of 54 Gy was prescribed in the planning target volume (PTV) in a normofractionated schedule. Patients were clinically monitored by endocrinologists, ophthalmologists, and radiation oncologists, and patients underwent MRI and hormonal analyses frequently. RESULTS: The median follow-up time was 54.94 months. None of the patients experienced acute side effects of grade 3 or higher. Regarding late side effects, new-onset hypopituitarism was observed in 14.3% of patients, with all patients exceeding the dose constraint to pituitary gland. Additionally, 25.7% reported subjective memory loss complaints, 4 underwent a neuropsychological assessment, and only 2 were confirmed. Furthermore, 8 out of 9 patients did not adhere to the maximum dose constraints for the hippocampus. Subjective auditory impairment was experienced by 31.3% of patients, with 4 out of 11 undergoing ENT evaluation, and 1 out of 4 describing radio-induced tubal catharsis. All 11 patients adhered to the cochlear constraints. Five cases of cataracts were reported, with all patients adhering to lens constraints, although they were significantly older than those without cataracts. Two cases of temporary cranial nerve deficits, one visual impairment, one epilepsy, and one transient ischemic attack were also documented.