Real-world experience with 11C-methionine PET in the management of acromegaly.

Abstract

L-[methyl-11C]-methionine-positron emission tomography (Met-PET) is a potentially important imaging adjunct in the diagnostic workup of pituitary adenomas, including somatotroph tumours. Met-PET can identify residual or occult disease and make definitive therapies accessible to a subgroup of patients who would otherwise require lifelong medical therapy. However, existing data on its use are still limited to small case series. Here, we report the largest single centre experience (N=61) in acromegaly. 189 cases of acromegaly were referred to our national Met-PET service in the last twelve years. For this analysis, we have reviewed outcomes in those 61 patients managed exclusively by our multidisciplinary team (single centre, single surgeon). Referral indications were: indeterminate MRI (n=38, 62.3%), occult residual (n=14, 23.0%), (radio-)surgical planning (n=6, 9.8%), occult de novo tumour (n=3, 4.9%). 33/61 patients (54.1%) underwent PET-guided surgery. 24/33 patients (72.7%) achieved complete biochemical remission following (re-)surgery. IGF-1 levels were reduced to <2xULN (upper limit of normal) in 6 of the remaining 9 cases, 3 of whom achieved levels of <1.1xULN compared to mean pre-operative levels of 2.4xULN (SD 0.8) for n=9. Only 3 patients developed single new hormonal deficits (gonadotropic/thyrotropic insufficiency). There were no neurovascular complications after surgery. In patients with persistent/recurrent acromegaly or occult tumours, Met-PET can facilitate further targeted intervention (surgery/radiosurgery). This led to complete remission in most cases (24/33) or significant improvement with comparatively low risk of complications. Met-PET should therefore be considered in all patients who are potential candidates for further surgical intervention, but present no clear target on MRI.