LAUSR

BACKGROUND Radiation therapy is a common treatment for meningiomas. Volume changes of meningiomas in response to radiation are not well-characterized. This study seeks to quantify the volume change of meningiomas following radiation. METHODS Data were collected from a retrospective single-institution database from 2005-2015. Tumors were measured using T1-weighted post-contrast MRI. Volumes were calculated using the ABC/2 ellipsoidal approximation. RESULTS 63 patients fit the inclusion criteria. 37 patients (59%) received radiation following resection, 19 (30%) received radiation alone, 4 (6%) received radiation following a biopsy, and 3 (5%) had unknown surgical status. 39 patients (62%) had skull base meningiomas. 43 tumors were WHO Grade I, and 12 tumors were WHO Grade II. 13 patients received radiosurgery, 43 received radiotherapy, and 7 received an unknown number of treatments. 8 patients did not attain local control and were excluded from volume analyses. WHO Grade I meningiomas saw an average of 33 ± 19% decrease in tumor volume; WHO Grade II tumor volumes decreased by an average 30 ± 23%. Radiosurgery saw an average volume decrease of 34 ± 13%, while radiotherapy resulted in volume decrease of 31 ± 21%. For those who achieved local control, there was an average decrease in tumor size of 30 ± 19%, 30 ± 22%, and 41 ± 19% over 0.5-1.5, 2.5-3.5, and >5 years, respectively. CONCLUSION Meningiomas treated with radiation exhibit non-linear decrease in size over time. The greatest decrease in tumor volume occurs within the first year and begins to plateau 5 years' post-radiation.