Analysis of Magnetic Resonance Imaging Volumetric Changes Following Hypofractionated Stereotactic Radiation Therapy for Benign Intracranial Neoplasms

To quantitatively assess volumetric changes following hypofractionated stereotactic radiation therapy (HFSRT) in patients treated for vestibular schwannomas, meningiomas, and non-functioning pituitary adenomas. We conducted a retrospective study of patients previously treated with LINAC-based hypofractionated stereotactic radiation therapy (HFSRT) for vestibular schwannomas, meningiomas, and non-functioning pituitary adenomas from two academic institutions. Patients received 25 Gy/5 fractions or 21 Gy/3 fractions to the tumor with a median 2 mm planning target volume (PTV). Following treatment, patients underwent clinical and radiologic follow-up with three-dimensional magnetic resonance imaging (3D-MRI) at 3-12 month intervals. Gross tumor volume (GTV) was outlined on each thin slice of contrast-enhanced T1 series before and on each scan after HFSRT. Volumetric changes were calculated and compared with neuroradiologist interpretations. There were 47 patients (24 men, 23 women) undergoing 197 MRI scans between 2002 and 2014. Tumor types included vestibular schwannoma (n = 34), meningioma (n = 9), and pituitary adenoma (n = 4). Median follow-up time was 30 months. Average GTV was 3.1 cm3, for the entire cohort. Few studies exist evaluating the role of 3D-MRI volumetric changes as a quantitative measure of tumor progression or regression after HFSRT in benign intracranial neoplasms. Volumetric measurement provides additional information to the radiation oncologist in the follow-up of these patients. Our results indicate that HFSRT provides excellent local control and minimal toxicities in patients with vestibular schwannomas, meningiomas, and non-functioning pituitary adenomas.