Use of somatostatin receptor nuclear imaging as a diagnostic adjunct in patients with dural-based lesions in the setting of concurrent or prior systemic malignancy

Introduction: The identification of gadolinium-enhancing dural-based lesions via screening brain MRIs in patients with active systemic malignancy (or a prior history of such) may pose a diagnostic challenge, potentially resulting in under/over-treatment of patients undergoing radiosurgery. Employing targeted nuclear imaging techniques can aid in determining the appropriate diagnosis of these ambiguous lesions, capitalizing on the expression of somatostatin receptors in meningiomas. In this study, we describe the integration of 111In-pentreotide SPECT imaging into the work-up of patients with dural-based lesions of uncertain pathology and use these data to direct optimal therapy.

Methods: A retrospective analysis was performed on patients who underwent 111In-pentreotide SPECT scans for intracranial lesion characterization. Each patient who subsequently received radiosurgery for either meningioma or concurrent metastasis had three distinct dose calculations generated using GammaPlan® (12.5Gy meningioma vs. 20 and 22Gy metastasis; 50% IDL). The difference in the adjusted volume of normal brain receiving 12Gy (V12adj=V12total−target volume) for lesions treated with appropriate doses for meningiomas versus metastatic disease was described. Statistical significance amongst treatment plans was tested via two-way ANOVA.

Results: Between 2014 and 2023, 29 patients underwent 111In-octreotide SPECT and traditional imaging (MRI; CT). 10 had histories of concurrent malignancy and/or metastatic disease. Mean age was 60.9yrs (20-81yrs) and 79.3% were female. The mean V12total for prescription doses were 14.42±3.9cm3 (12.5Gy), 28.29±7.3cm3 (20Gy), and 32.11±8.2cm3 (22Gy) at 50% isodose. Adjusted values (V12adj) for 12.5Gy, 20Gy, and 22Gy treatment plans were 3.01±0.6cm3, 16.89±3.93cm3, and 20.71±4.83cm3. Tukey’s post-hoc demonstrated significant differences between means in the 12.5Gy and 20Gy (13.87±3.8cm3; p=0.0011) and 12.5Gy and 22Gy (17.69±3.2cm3; p< 0.0001) groups.

Conclusion : Molecular imaging in conjunction with traditional modalities may be useful in differentiation between benign lesions, such as meningiomas, and dural metastases for patients undergoing radiosurgery and offers a modality for optimal dose determination.