OUTCOMES AND TOXICITIES FOLLOWING CONVENTIONAL RADIATION THERAPY FOR PITUITARY NEUROENDOCRINE TUMOURS (PITNETS)

Purpose:

Radiation is an effective treatment modality for recurrent pituitary neuroendocrine tumours (PitNETs). Both stereotactic radiosurgery (SRS) and conventional radiation are the two main treatment paradigms for these tumours depending on the distance to the optic apparatus. The aim of the current study was to retrospectively assess outcomes and toxicities following conventional radiation in patients with PitNETs and eventually compare these findings to SRS cohorts.

Materials and Methods:

A single-centre, retrospective, population-based analysis was performed. Patients with functional and non-functional PitNETS treated with conventionally fractionated radiation (50 Gy in 25 fractions) between 2000-2023 were included. The primary outcome was local tumour control and secondary outcomes included various toxicities (hormonal, optic, vascular, edema, and second tumours).

Results:

194 patients met criteria and were included in the final analysis (100 females [52%] and 94 males [48%]). The median age at initial diagnosis was 47.2 years (range=13.9-92.yrs) and 134 (69%) tumours were non-functional. Most patients had 1-4 surgeries prior to radiation (98.5%). The median duration of follow-up after completion of radiation was 6.8 years (range=0.4-23.1yrs). Local recurrence was seen in 8 patients (4.1%), where 5 were functional (2.6%) and 3 were non-functional (1.5%). The median time to local recurrence following radiotherapy was 6.1 years (range=0.5-14.8yrs) and these patients were subsequently treated with gamma-knife radiotherapy (n=4), surgery (n=3), or convention radiation (n=1). Pituitary dysfunction requiring pituitary hormone replacement following radiation was seen in 42 patients (21.6%), and 76 patients (39.2%) were on pituitary replacement following surgery but prior to radiation. Of those requiring pituitary replacement, 30 (71.4%) were for hypothyroidism, 29 (69.0%) were for adrenal insufficiency, 10 (23.8%) were for hypogonadism, and 1 (2.5%) was for diabetes insipidus. The median time to initiating pituitary replacement was 5.6 years (range=0.2-19.8yrs). A secondary tumour (vestibular schwannoma) was seen in 1 patient (0.52%) twelve years following radiation. There was no optic, vascular or edematous toxicities.

Conclusions:

Here, we provide an updated, large population-based study to investigate conventionally fractionated radiotherapy for PitNETs, which confirms this technique is a safe and effective treatment. The main toxicity of this treatment is pituitary dysfunction that requires hormone replacement. Further analysis comparing conventional radiation to SRS is forthcoming.